Changes in ovarian function and gonadotropin secretion preceding the onset of nutritionally induced anestrus in Bos indicus heifers

The aim of this study was to monitor endocrine and ovarian changes immediately preceding the onset of nutritionally induced anestrus. Daily blood samples were obtained from 14 postpubertal heifers for one estrous cycle (initial estrous cycle). Subsequently, heifers designated "restricted" were given a limited diet (n = 9), and daily blood samples were obtained for approximately 21 days preceding onset of anestrus (anovulatory cycle). Controls were allowed ad libitum dietary intake (n = 5), and daily blood samples were collected for a complete estrous cycle during a time period that coincided with that preceding onset of anestrus in restricted heifers. Plasma samples were assayed for LH, FSH, progesterone, and estradiol-17 beta. The ovaries of all heifers were examined daily using transrectal ultrasonography from the initial until the final or anovulatory estrous cycles to determine changes in growth of follicles and corpora lutea. Anestrus was defined as failure of ovulation of the dominant follicle following luteolysis. When anovulatory and initial estrous cycles in restricted heifers were compared, mean concentrations of LH were lower (p < 0.01), and diameters of dominant follicles were smaller (p < 0.01); mean concentrations of estradiol-17 beta were also lower in the three days following luteolysis (p = 0.06), but concentrations of FSH appeared to be higher (p = 0.003); maximum diameters of corpora lutea were smaller (p < 0.001), but duration of luteal phases and concentrations of progesterone preceding luteolysis were similar (p > 0.10). In controls, no differences were found between estrous cycles for any of these variables. It is concluded that failure of ovulation, following reduced dietary intake, resulted from insufficient circulating LH to stimulate maturation of the ovulatory follicle.     

Inhibin secretion in the mare: localization of inhibin alpha, betaA, and betaB subunits in the ovary

To determine the source of circulating inhibin and estradiol-17beta during the estrous cycle in mares, the cellular localization of the inhibin alpha, betaA, and betaB subunits and aromatase in the ovary was determined by immunohistochemistry. Concentrations of immunoreactive (ir-) inhibin, estradiol-17beta, progesterone, LH, and FSH in peripheral blood were also measured during the estrous cycle in mares. Immunohistochemically, inhibin alpha subunits were localized in the granulosa cells of small and large follicles and in the theca interna cells of large follicles, whereas inhibin betaA and betaB subunits were localized in the granulosa cells and in the theca interna cells of large follicles. On the other hand, aromatase was restricted to only the granulosa cells of large follicles. Plasma ir-inhibin concentrations began to increase 9 days before ovulation; they remained high until 2 days before ovulation, after which they decreased when the LH surge was initiated. Thereafter, a further sharp rise in circulating ir-inhibin concentrations occurred during the process of ovulation, followed by a second abrupt decline. After the decline, plasma concentrations of ir-inhibin remained low during the luteal phase. Plasma estradiol-17beta concentrations followed a profile similar to that of ir-inhibin, except during ovulation, and these two hormones were positively correlated throughout the estrous cycle. Plasma FSH concentrations were inversely related to ir-inhibin and estradiol-17beta. These findings suggest that the dimeric inhibin is mainly secreted by the granulosa cells and the theca cells of large follicles; granulosa cells of small follicles may secrete inhibin alpha subunit, and estradiol-17beta is secreted by the granulosa cells of only large follicles in mares.     

Fate of the dominant follicle, embryonal survival, and pregnancy rates in dairy cattle treated with prostaglandin F2 alpha and progestins in the absence or presence of a functional corpus luteum

Our objective was to examine the role of progestin type on serum concentrations of progesterone (p4) and estradiol-17 beta (E2), ovarian follicular dynamics, and fertility in cattle in the presence or absence of a corpus luteum (CL) in an estrus synchronization scheme using progestin and PGF2 alpha. In Exp. 1, 325 cows and heifers were given one injection of PGF2 alpha (d 0) and then assigned randomly within parity to five treatments: to receive a second PGF2 alpha injection 14 d later (control); to receive norgestomet (NORG) for 7 d beginning on d 8, with a second PGF2 alpha injection given either 1 d (NORG + no CL) or 6 d (NORG + CL) after insertion; or to receive a P4-releasing intravaginal device (PRID) in lieu of norgestomet at comparable times. Presence or absence of a CL was based on concentrations of serum P4 on d 14. Pregnancy rates after insemination were greater (P < .01) with luteal treatments than with nonluteal treatments. Embryonal survival between two stages of pregnancy was 87.6%. In Exp. 2, ovarian structures in 50 cows were examined daily using ultrasonography and the same five treatments. Diameter of the ovulatory follicle was greater (P < .05) with the nonluteal treatments (NORG and PRID + no CL) than with the control and luteal treatments (PRID and NORG + CL). Replacement of the dominant follicle during progestin treatment was altered by treatment (luteal status) and stage of the estrous cycle. Fertility was not enhanced by exogenous progestins when a CL was present. In the absence of a CL, progestin (P4 less than NORG at the doses used) reduced fertility by increasing E2 and the diameter of the ovulatory follicle and decreasing turnover of dominant follicles.     

Altering conception of dairy cattle by gonadotropin-releasing hormone preceding luteolysis induced by prostaglandin F2 alpha

The objective of these experiments was to determine the effect on fertility of GnRH when used in conjunction with one or two injections of PGF2alpha. In Experiment 1, GnRH was administered 7 d before the second of two injections of PGF2alpha (14 d apart). The control group received two injections of PGF2alpha without GnRH. Conception was reduced from 63.5% for 74 controls to 48.7% for the 79 heifers and cows that had been treated with GnRH, but estrus detection and pregnancy rates were similar. In Experiment 2, 85 heifers and cows received GnRH at a random stage of the estrous cycle, followed in 7 d by PGF2alpha. Thirty to 32 h after PGF2alpha, a second dose of GnRH was given to induce ovulation of the preovulatory follicle, followed by one fixed-time insemination 18 to 19 h later (treatment designated as GnRH, PGF2alpha, and GnRH). Controls (n = 85) were given PGF2alpha and inseminated at estrus. Although conception rate was not different, one fixed-time insemination after the GnRH, PGF2alpha, and GnRH treatment tended (35.3%) to reduce fertility compared with effects of the control (47.1%). It is unclear how an injection of GnRH during the intervening week between two injections of PGF2alpha reduced fertility in Experiment 1. However, in Experiment 2, when GnRH was given 7 d before one injection of PGF2alpha and when ovulation was induced with a second GnRH injection, one fixed-time insemination seemed to produce acceptable fertility in dairy cows but probably less than that when inseminations were based on detected estrus.     

Characteristics of prolonged dominant versus control follicles: follicle cell numbers, steroidogenic capabilities, and messenger ribonucleic acid for steroidogenic enzymes

Cattle with low (subluteal) levels of plasma progesterone develop a persistent dominant follicle; plasma estradiol and LH pulse frequency are elevated, and fertility subsequent to the ovulation of a prolonged dominant follicle is compromised. The hypotheses were 1) that prolonged dominant follicles produce more estradiol because they have theca and granulosa cells with an enhanced capacity to produce androgen and estradiol, respectively, and 2) that these changes in steroidogenic capacity are paralleled by concomitant changes in mRNA for the appropriate steroidogenic enzymes. Prolonged dominant follicles were induced by treating Holstein heifers with exogenous progesterone via an intravaginal controlled internal drug-release device (CIDR) from Day 14 to 28 of the cycle. Prolonged dominant follicles were collected just before (CIDRb, Day 28; n=4) or 24 h after (CIDRa, Day 29; n=4) CIDR removal, and their steroidogenic capacity was compared to that of growing, control dominant follicles obtained just before (CONTb, n=4) or 24 h after (CONTa, n=4) a luteolytic injection of prostaglandin F2alpha during the late luteal phase. After natural luteolysis, CIDR heifers maintained subluteal concentrations of progesterone (1-2 ng/ml) and had higher estradiol and LH pulse frequency than control heifers, as expected. In CIDR heifers, prolonged dominant follicles were present on the ovary for a longer time, reached a larger diameter, and had more granulosa cells and a larger mass of theca than dominant follicles from control heifers (p < 0.05). Concentrations of steroids in follicular fluid, estradiol secretion by granulosa cells in vitro, and levels of mRNA for steroidogenic enzymes in theca and granulosa cells provided no evidence for greater capacity of theca and granulosa cells of CIDR follicles to produce androgen and estradiol. In fact, follicular fluid estradiol and mRNA for P450 aromatase were higher after luteolysis than before in control animals (p < 0.05) but not after CIDR removal in treated animals. Therefore, the data do not support the hypotheses. Rather it is suggested that prolonged dominant follicles produce more estradiol because they have more granulosa cells and a larger mass of theca than control dominant follicles. In contrast, progesterone concentrations in the follicular fluid increased in CIDRa relative to CIDRb follicles (p < 0.05), a change that did not occur in control follicles; and granulosa cells from CIDRa follicles secreted more progesterone than granulosa cells from any other group. The increased capacity of CIDRa follicles to secrete progesterone suggests premature luteinization, which could contribute to decreased fertility in cattle that ovulate a prolonged dominant follicle.     

P300 subcomponents reflect different aspects of psychopathology in schizophrenia

With the results presented in this paper we devised an alternative method to precisely date the rat endometrium in relation to the estrous cycle. This is done by the exclusive use of scanning electron microscopy. Owing to its short estrous cycle (4 to 6 days, depending on age), the rat is ideally suited for the examination of cyclic changes occurring in the uterine epithelium. The cycle stage of rats predated by vaginal smear cytology was verified through the measurement of hormones relevant to the estrous cycle, i.e. estradiol-17-beta (E2), progesterone (P), luteinizing hormone (LH), and follicle stimulating hormone (FSH). Based on scanning electron images surface changes could thus be correlated to the cyclic variations of blood levels of sex hormones. The appearance of pseudoglands, the most prominent aspect during the cycle, is correlated with decreasing estrogen and rising progesterone levels. Pseudoglands are formed by apoptosis and necrosis of epithelial cells, and are most numerous during estrus. They had in previous studies been classified as genuine uterine glands.     

Prostaglandin F2alpha-induced luteolysis of aging corpora lutea in hysterectomized pigs

Prostaglandins primarily of uterine origin play an important role in parturition. Hysterectomy of nongravid pigs early in the luteal phase maintains luteal function until about Day 150, whereas the duration of normal pregnancy is about 114 days. A precisely timed peak release of relaxin and coincident decrease in progesterone secretion in unmated hysterectomized gilts are similar to hormonal changes that occur a few hours before parturition. It is hypothesized that prostaglandin F2alpha (PGF2alpha) in hysterectomized pigs mimics abrupt changes in ovarian and pituitary hormone secretion seen before normal parturition and in early lactation. Unmated Yorkshire gilts were hysterectomized on Days 6-8 of a normal estrous cycle, and at 1200 h on Day 113, they were given an i.m. injection of 30 mg PGF2alpha-trihydroxymethylaminomethane (THAM) salt or PBS. None of these gilts expressed behavioral estrus immediately after PGF2alpha or vehicle treatment. On Day 113, PGF2alpha increased peak relaxin (60 ng/ml) compared with that of controls (34 ng/ml; p < 0.01), whereas progesterone decreased abruptly (4 vs. 16 ng/ml in PGF2alpha and PBS; p < 0.01). Prolactin remained at < 5 ng/ml from Day 98 to 120 in controls but peaked at 33 ng/ml immediately after PGF2alpha treatment on Day 113, and then decreased to levels similar to those of controls on Day 120. Sequential bleeding revealed an acute growth hormone release (4.5 ng/ml) immediately after PGF2alpha injection and return to basal levels (< 0.6 ng/ml) on Days 114-120. PGF2alpha induced abrupt shifts in progesterone, relaxin, prolactin, and growth hormone secretion in hysterectomized gilts that mimicked hormone changes seen in late pregnancy, parturition, and early lactation. These findings provide new insight into the role of PGF2alpha in abruptly changing hormone secretions by aging corpora lutea and the pituitary gland even in the absence of conceptuses or the uterus in the pig.     

Follicle size-dependent induction of prostaglandin G/H synthase-2 during superovulation in cattle

Under physiological conditions, prostaglandin G/H synthase-2 (PGHS-2) is induced in bovine preovulatory follicles by the endogenous surge of gonadotropins. To characterize the pattern of follicular PGHS-2 expression during superovulation in cattle, heifers were treated with exogenous FSH and ovulation was induced with hCG. Animals were ovariectomized 0, 18, and 24 h post-hCG, and extracts of follicles > or = 6 mm were analyzed by Western blotting. Follicular fluid concentrations of prostaglandin (PG) E2, PGF2alpha, progesterone, and estradiol-17beta were determined by RIAs, and the morphology of the cumulus oocyte complex was examined. Results showed that PGHS-2 protein was absent in all follicles isolated at 0 h post-hCG (n = 119) and in small follicles (6 to < 8 mm) isolated between 0 and 24 h post-hCG (n = 27 follicles). In contrast, 12.3% of medium (8 to < 10 mm) and 43.7% of large (> or = 10 mm) follicles were PGHS-2-positive at 18 h post-hCG, and these percentages rose at 24 h to 45.9% and 91.0% in medium and large follicles, respectively (p < 0.05). Follicular fluid concentrations of PGE2 and PGF2alpha were low in follicles isolated at 0 h and increased only in PGHS-2-positive follicles isolated 24 h post-hCG (p < 0.05). Concentrations of progesterone and estradiol-17beta at 0 h were 28.2 +/- 5.8 and 291.8 +/- 13.0 ng/ml, respectively, and a shift from estradiol-17beta to progesterone dominance (luteinization) occurred at 24 h post-hCG only in PGHS-2-positive follicles. Also, expansion of the cumulus oocyte complex was detected at 24 h post-hCG only in PGHS-2-positive follicles. Lack of PGHS-2 induction in follicles of ovulatory size (> 8 mm) was associated with an apparent failure to respond to hCG (absence of luteinization and cumulus expansion). Collectively, these results demonstrate the presence of a time- and follicle size-dependent induction of PGHS-2 in bovine follicles during superovulatory treatment and suggest that PGHS-2 expression can be used as a marker for follicular commitment to ovulation during ovarian hyperstimulation protocols.     

Effect of prostaglandin F2 alpha-and gonadotropin releasing hormone-induced luteinizing hormone releases on ovulation and corpus luteum function of beef cows

Luteinizing hormone (LH) concentrations were measured in suckled beef cows treated during the postpartum period with prostaglandin F2 alpha (5 mg Alfaprostol; PGF2 alpha) and then gonadotropin releasing hormone (100 micrograms Cystorelin 30 h after PGF2 alpha; GnRH). The objective was to determine if PGF2 alpha would cause a release of LH in the absence of progesterone and affect the GnRH-induced LH release and ovulation (Experiment 1). LH concentrations increased (P < 0.05) after PGF2 alpha treatment in both anestrous and cyclic cows but to a greater extent (P < 0.05) in anestrous cows. The GnRH-induced LH release and ovulation response in previously anestrous cows were greater (P < 0.05) when PGF2 alpha was administered 30 h earlier. In Experiment 2, 49 beef cows received PGF2 alpha (5 mg Alfaprostol) and GnRH (100 micrograms Cystorelin) 30 h later to determine if the profile of the preovulatory LH surge was associated with the occurrence of subnormal luteal phases in postpartum beef cows suckling calves. Cows that had normal luteal phases had a greater (P < 0.05) mean area under the GnRH-induced LH response curve and a greater (P < 0.05) mean GnRH-induced LH peak amplitude than cows that had subnormal luteal phases. In summary, results suggest that PGF2 alpha may exert a fertility effect by causing a LH release independent of progesterone withdrawal; administration of PGF2 alpha 30 h before GnRH elevated the GnRH-induced LH release and ovulation response. In addition, cows with subnormal luteal phases had GnRH-induced LH surges of less area and peak amplitude than cows with normal luteal phases.     

Interleukin-1 beta modulates prostaglandin and progesterone production by primate luteal cells in vitro

Increasing evidence suggests that cytokine products of the immune system may play a regulatory role in corpus luteum regulation in several species. The role of cytokines in primate luteal function, however, remains unclear. In the present study we examined the effects of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha), and interferon-gamma (IFN-gamma) on progesterone and prostaglandin (PGE2, PGF2 alpha) production by primate luteal cells in vitro. Specifically, corpora lutea were removed from normally cycling cynomolgus monkeys (n = 30 corpora lutea) during either the early (Days 3-5 after the estimated LH surge), mid (Days 8-10), or late (Days 12-14) luteal phase of the menstrual cycle. The corpora lutea were dispersed into individual cells using collagenase, DNase, and hyaluronidase. Approximately 50,000 viable luteal cells per tube were incubated in Ham's F-10 medium with increasing concentrations of IL-1 beta (0.1-10 ng/ml), TNF alpha (1-100 ng/ml), or IFN-gamma (10-1000 U/ml) in the presence and absence of hCG for 8 h at 37 degrees C. TNF alpha and IFN-gamma had no effect on progesterone PGE2, or PGF2 alpha production during any phase of the cycle at the doses tested. In contrast, IL-1 beta significantly stimulated PGF2 alpha production in a dose-dependent manner during the mid and late luteal phases (p < 0.05). Human CG alone had no effect on PGE2 or PGF2 alpha production by dispersed luteal cells in vitro but inhibited IL-1 beta-stimulated PGF2 alpha production. As expected, hCG stimulated progesterone production by primate luteal cells in vitro. Interestingly, IL-1 beta inhibited this hCG stimulation of progesterone production. In summary, these date suggest that IL-1 beta is a potentially important modulator of prostaglandin production by the primate corpus luteum. In view of this, cytokine-mediated changes in prostaglandin production by the primate corpus luteum may participate in the physiological regulation of luteal function.     

Duration of treatment with progesterone and regression of persistent ovarian follicles in cattle

The objective of the present study was to determine the duration of elevated concentrations of progesterone necessary to induce atresia of persistent ovarian follicles. Heifers were administered 25 mg of PGF2alpha on d 6 and 7 (d 0 = d of synchronized estrus) and a norgestomet implant from d 6 to 14. Ovaries were monitored by ultrasonography, and blood samples were collected on d 3, 5, 7, 9, 11, and 12 and daily from d 14 until ovulation. On d 12, heifers received either two progesterone-releasing intravaginal devices (PRID) for 6 h (6-h; n = 5), two PRID for 24 h (24-h; n = 5), or no treatment (CON; n = 5). Blood samples were collected at 15-min intervals from h -6 to 30 (PRID insertion = h 0) and analyzed for concentrations of LH. Characteristics of LH secretion were determined for consecutive 6-h periods (Period 0 to 5). Hourly blood samples, collected from h 0 to 29, were analyzed for concentrations of 17beta-estradiol (estradiol) and progesterone. The dominant ovarian follicles present on d 7 increased in size to 15.4+/-.3 mm on d 12 ("persistent follicle"). Following removal of the PRID and norgestomet implants, atresia of persistent follicles and ovulation of new follicles were induced in one of five and in four of five heifers in the 6-h and 24-h treatments, respectively. Persistent follicles ovulated after withdrawal of norgestomet in all other heifers. Concentrations of progesterone were increased from h 1 to 7 in the 6-h and h 1 to 26 in the 24-h treatment. Frequency of LH pulses was reduced (P < .05) during Periods 1 to 2 in the 6-h and Periods 1 to 5 in the 24-h treatment relative to the CON treatment. By h 10, concentrations of estradiol in the 6-h and 24-h treatments were lower (P < . 05) than in the CON treatment. This suppression continued through h 29 in the 24-h treatment (P < .05), whereas concentrations in the 6-h treatment were intermediate to those of the CON and 24-h treatments after h 14. Suppression of pulsatile LH release and estradiol secretion was evident with 6 and 24 h of treatment with progesterone, but only the 24-h treatment induced atresia of persistent follicles in a majority of the heifers.     

Ontogeny of oxytocin receptors and oxytocin-induced stimulation of prostaglandin synthesis in prepubertal heifers

Developmental aspects of oxytocin (OT) receptors (OTR) in uterine tissues before puberty are not known. Bovine ovaries secrete some estradiol, but no progesterone, before puberty; the circulating levels of estradiol are between 1 and 3 pg/ml until puberty. Cross-bred Angus-Brahman heifers, in which puberty occurs around 12 months of age, were used to determine the concentrations of OTR from the late fetal stage to adulthood. PGF2alpha release in response to OT was determined in 3-, 6-, and 9-month-old heifers (n = 4 each). Myometrium, endometrium, and cervical mucosa were obtained from 3-week-old, 3-month-old, 6-month-old, and 9-month-old heifers and from adult cows at estrus. Whole uterus and cervix were taken from third trimester fetuses and at birth. [3H]OT binding and specificity, localization of immunoreactive (ir) OTR, OTR messenger RNA, and OT-induced release of PGF2alpha were determined. The uterus from fetuses and the neonate expressed OTR messenger RNA and bound [3H]OT. At 3 weeks of age, OTR concentrations per mg protein were very low, but at 3 months of age they had increased markedly in all three tissues. At 6 and 9 months of age, levels of OTR had risen further and were similar to those in adult cows at estrus. Prepubertal uterus also possessed separate vasopressin VP1 subtype receptors. The ir-OTR was localized in luminal epithelial cells of endometrium and cervical mucosa, most of which were ir positive, whereas in myometrium, clusters of ir-OTR-positive cells were found among large numbers of ir-OTR-negative cells. The PGF2alpha response to OT was insignificant in heifers of all age groups, in contrast to that in cows at estrus. Endometrial cells from 4- to 5-month-old heifers did not respond to OT with PG release in the absence or presence of added arachidonic acid. Tumor promoters, lipopolysaccharide, and interleukin-2 also failed to elicit PG release in vitro, although they induced PG release in similar cell cultures from cyclic cows. In summary, uterine tissues of prepubertal heifers have high levels of OTR, which appear to be developmentally regulated. These receptors are not coupled to PG synthase, or alternatively, the PG synthase gene is not expressed before puberty, possibly because the tissues have had no previous exposure to progesterone.     

Fertility in estrus-cycling and noncycling virgin heifers and suckled beef cows after induced ovulation

A procedure was developed to either induce or synchronize ovulation in heifers and suckled cows. Beef females were assigned to two breeding programs: 1) two injections of prostaglandin F2alpha (PGF2alpha) given 14 d apart to synchronize estrus (PGF2alpha control; n = 179), with inseminations 12 to 16 h after detected estrus or at 80 h in the absence of estrus, or 2) two injections of PGF2alpha (d -14 and 0) plus 100 microg of GnRH on d -7 when 6 mg of norgestomet was implanted (PGF2alpha/NORG/GnRH treatment; n = 173). Implants were removed 24 h after the second PGF2alpha injection (d +1) and females were inseminated 12 to 16 h after detected estrus until 54 h after PGF2alpha. The remaining cattle were given a second 100-microg GnRH injection 54 h after PGF2alpha and inseminated 18 to 20 h later. Percentages of noncycling females with subsequently elevated progesterone (P4) on d 0 or +1 were not different between treatment groups (20.4 vs 25%), but conception rate was greater (P < .05) in noncycling treated females than in noncycling controls (55 vs 12.8%). Conception rates in cycling (59.2%) and noncycling (62.2%) treated females were similar to those in cycling controls (56.2%) but greater (P = .06) than those in noncycling controls (26.5%). Conception rates in treated females inseminated 12 to 16 h after detected estrus (63.1%) or at one fixed time (58.3%) were similar to those in controls inseminated 12 to 16 h after detected estrus (68.7%). This treatment procedure produced fertility after one timed insemination that was equal to controls inseminated after detected estrus and induced equally fertile ovulations in noncycling heifers and cows.     

Development of a progestin-based estrus synchronization program: II. Reproductive response of cows fed melengestrol acetate for 14 days with injections of progesterone and prostaglandin F2alpha

We tested the efficacy of an estrus control system designed to provide optimal control of follicular development. In Exp. 1, postpartum cows (n = 133) and yearling heifers (n = 57) were fed either .5 mg x female(-1) x d(-1) of melengestrol acetate (MGA) or the carrier for MGA from d -13 to d 0 (d 0 = last day of MGA feeding). All females received 25 mg of PGF2alpha (i.m.) on d -13 and 0. On d -6, cows and heifers fed MGA were administered an i.m. injection of progesterone (200 mg; MGA/P4), and those fed the corn carrier (2XPGF2alpha) received no progesterone. Beginning on d 1, females were bred by AI from d 1 to at least d 5. During the estrus synchronization period (d 1 to d 5), more (P < .05) postpartum cows were observed in estrus (70.1 vs 42.4%), the timing of estrus was more (P < .05) precise, conception rate was similar, and pregnancy rate was higher (P < .05) in the MGA/P4 than in the 2XPGF2alpha treatment. More (P < .05) cows that were anestrous at the beginning of the breeding season were in estrus during the synchronization period in the MGA/P4 (55.8%) than in the 2XPGF2alpha (28.6%) treatment. In heifers, estrus was synchronized in over 90% of females, and neither conception nor pregnancy rate during the synchronization period differed between treatments. In Exp. 2, postpartum cows (n = 122) and heifers (n = 84) received treatments (MGA/P4 or 2XPGF2alpha) as described for Exp. 1 with one exception. In the MGA/ P4 treatment, progesterone was administered on d -7 rather than d -6. Females were bred by AI from d 1 to 5. The estrus response and conception rate during the synchronization period did not differ between treatments for either cows or heifers. We conclude that the progestin-based estrous synchronization system used in this study effectively synchronized an estrus of normal fertility in cyclic cows and induced a majority of anestrous cows to reinitiate estrous cycles.     

A special closure system of the gastrointestinal tract of the rat (author''s transl)

Serial determinations of FSH, LH, estradiol-17 beta and progesterone in plasma and of total gonadotropins, total estrogens and pregnanediol in urine were performed in 10 adolescent girls between 15 and 19 years of age. Two types of menstrual cycles could be distinguished. The first type is characterized by a nearly normal pattern of FSH, while a preovulatory rise of estradiol-17 beta and an LH-peak is still missing. Only few days prior to menstrual bleeding a small rise of estradiol and progesterone in plasma as well as of estrogens and pregnanediol in urine can be seen, being equivalent to a short luteinization of the follicle without ovulation taking place. The second type already shows all criteria of a regular ovulatory cycle. However the plasma level of LH, estradiol and progesterone and the excretion of estrogens and pregnanediol are still below the average values of control cycles of adult women. On the basis of the hormonal pattern and a shortened luteal phase, a relative insufficiency of this type of cycles is still evident. These studies demonstrate, that the cyclic ovarian function postmenarchial develops gradually and that the onset of ovulation is a marked step in this development. This process of maturition, which is due to the gradual development of the positive feedback of estrogens on the release of LH by the pituitary gland, allows to distinguish in adolescence between cycles before and after maturition of the feed-back mechanism in the ANS.     

Acute effects of prostaglandin F2 alpha, luteinizing hormone, and estradiol on second messenger systems and on the secretion of oxytocin and progesterone from granulosa and early luteal cells of the ewe

Previous reports have suggested that gonadotropins, estradiol, and prostaglandin F2 alpha (PGF2 alpha) have varying effects on progesterone and oxytocin synthesis or secretion in cultured granulosa and luteal cells collected at different stages of the estrous cycle. The experiments reported here were designed to investigate whether effects of these agonists on secretion of hormones and their coupling to second messenger systems changed around the time of ovulation. Granulosa cells and Day 2 luteal cells of the ewe were cultured for three days and then treated for 30 min with varying doses of PGF2 alpha, LH, or estradiol. LH increased intracellular cAMP at both stages, but granulosa cells were more responsive in terms of both minimum effective dose (10 compared with 100 ng/ml) and degree of stimulation. LH caused no change in intracellular inositol phosphate levels. Both granulosa and early luteal cells responded to LH treatment by an increase in progesterone output in a dose-responsive fashion. PGF2 alpha increased inositol phosphate accumulation in cells collected at both stages of the cycle. All doses tested (10(-6)-10(-8) M) stimulated the release of oxytocin into the culture medium from both granulosa and luteal cells. Progesterone secretion was also increased, but only at the highest dose (10(-6) M). Estradiol treatment (10(-6) M) did not affect either the inositol phosphate or cAMP second messenger systems, but it did inhibit the secretion of oxytocin from granulosa cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteal dysfunction in ewes induced to ovulate early in the follicular phase

The purpose of this investigation was to determine whether the timing of ovulation induction during the follicular phase is a determinant of consequent luteal function. Ewes were treated on day 14 of the estrous cycle with PGF2alpha to synchronize luteal regression and 12 or 36 h later with an ovulatory dose of GnRH. Luteal phase serum progesterone concentrations of normal magnitude were characteristic of animals elicited to ovulate by GnRH injection 36 h after PGF2alpha treatment. Follicles stimulated at 12 h of the induced follicular phase formed subfunctional corpora lutea that were deficient in large steroidogenic cells. Endometrial gland development was attenuated in ewes exhibiting luteal insufficiency. The pathophysiology of the luteal defect was associated with a retrospective lack of granulosal cells in preovulatory follicles not adequately primed by estradiol. Preovulatory LH surges were not affected by the time of GnRH treatment. Corpus luteum rescue indicative of maternal recognition of pregnancy occurred in inseminated ewes that were injected with GnRH 36 h after PGF2alpha. Gonadotropic stimulation 12 h after PGF2alpha typically resulted in gestational failure; a marginal improvement in the pregnancy rate was attained by progesterone supplementation. We suggest that premature induction of ovulation compromises the estrogen-mediated succession of granulosal cell proliferative events that necessitate the formation of a fully competent corpus luteum.     

Effects of dietary gossypol consumption on metabolic homeostasis and reproductive endocrine function in beef heifers and cows

Our objectives were to determine the effects of incremental increases in dietary gossypol on metabolic homeostasis and reproductive endocrine function in postpubertal beef heifers and the long-term effects of elevated dietary gossypol on various metabolic and reproductive endocrine characteristics in mature cows. In Exp. 1, heifers (n = 6/group) were fed either 0, .5, 2.5, 5, 10, or 20 g.animal-1 x d-1 of dietary free gossypol for 62 d. Erythrocyte membrane osmotic fragility was increased (P < .0001) in both the 10- and 20-g groups. Slight alterations in plasma concentrations of sorbitol dehydrogenase and K+ were also detected in the latter group. Treatment did not affect ADG, body condition scores, or concentrations of progesterone during the estrous cycle; however, mean concentrations of LH were higher (P < .001) in heifers fed 20 g/d of gossypol than in heifers in all other groups. In Exp. 2, lactating cows (n = 17) exhibiting regular estrous cycles were fed a control (no gossypol, n = 8) or high-gossypol (20 mg.kg BW-1 x d-1 free gossypol, n = 9) diet for 33 wk. Mean BW and body condition scores did not differ during the feeding period. Erythrocyte membrane fragility was greater (P < .05) in the high-gossypol than in the control group. Magnitude of the preovulatory LH surge, luteal phase concentrations of progesterone, follicular fluid concentrations of estradiol and progesterone, in vitro granulosa cell estradiol production, and 60-d pregnancy rates were similar between groups. The amounts of gossypol fed in these experiments are not likely to affect reproductive performance adversely in beef heifers or cows.     

Induced luteolysis in the primate: rapid loss of luteinizing hormone receptors

The molecular mechanisms involved in luteolysis are still unclear in the primate. This study aimed to investigate the effect of induced luteolysis on the ovarian luteinizing hormone (LH) receptor and the steroidogenic enzyme, 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in the marmoset monkey. Luteolysis was induced in the mid-luteal phase either directly by systemic prostaglandin F2alpha (PGF2alpha), or indirectly by LH withdrawal using systemic gonadotrophin releasing hormone antagonist (GnRHant) treatment. The LH receptor was studied by isotopic mRNA in-situ hybridization and in-situ ligand binding and 3beta-HSD expression was studied using isotopic mRNA in-situ hybridization and immunohistochemistry. Induced luteolysis was associated with a reduction in the expression of LH receptor (P < 0.0001) and 3beta-HSD mRNA, closely followed by a reduction in the LH receptor (P < 0.05) and 3beta-HSD protein concentrations within 24 h. There were no differences in the findings whether luteolysis was induced with PGF2alpha or GnRHant. This study shows that disparate mechanisms to induce luteolysis in the primate result in an identical rapid loss of the LH receptor and 3beta-HSD. In conclusion, induced luteolysis leads to rapid loss of the steroidogenic pathway in luteal cells.