Spontaneous and prostaglandin- or oxytocin-induced motility of rat ovaries isolated during different stages of the estrous cycle: effects of norepinephrine

Ovaries isolated from rats in different stages of the sex cycle were explored for spontaneous or drug-induced contractile activity. The number of spontaneously active ovaries as well as the magnitude of the isometrically developed tension and frequency of contractions were greater during the periovulatory interval (late proestrus and estrus) than during early proestrus or metestrus. Furthermore, during estrus or late proestrus the left ovaries exhibited a mechanical activity significantly greater than that of the right ovaries. The oxytocin-triggered motility was clearly more marked immediately prior to ovulation (late proestrus) and greater in left ovaries than in right ovaries. In contrast, the contractions induced by prostaglandin F2alpha were similar during early proestrus and late proestrus. Ovarian contractile reactivity to norepinephrine indicated the presence in the tissue of alpha- and beta-adrenergic receptors. During early proestrus this agent stimulated the motility of left and right ovaries, whereas close to the ovulatory interval (late proestrus) it depressed the contractions of left ovaries. This last influence was blocked by propranolol. The existence of a close relationship between ovarian contractile activity and ovulation is reinforced by the present results in the rat. A tentative participation of oxytocin is also suggested. In addition, the influences of other possible regulatory agents of ovarian contraction, such as catecholamines and prostaglandins, are presented and discussed.     

Effect of chlordiazepoxide on schedule-controlled responding and schedule-induced drinking

Polyovular follicles and polynuclear ova have been recorded to occur only in 5 goats out of 24 goats of ages between 2 months 24 days and 5 years 2 months 18 days, studied. These structures were recognized at proestrus, estrus and metestrus only but never in the animals over 1 year of age. Polyovular and polynuclear follicles with no apparent degenerative changes were seen at estrus whereas degenerating ones were commonly seen at proestrus and metestrus also.     

Cytosolic estrogen receptor concentrations in the lumbosacral spinal cord fluctuate during the estrous cycle

Estrogen responsive neurons have been anatomically identified with autoradiographic and immunohistochemical techniques and their distribution mapped in the lumbosacral spinal cord of female rats. Such neurons contain estrogen receptors (ERs). The present study was undertaken to: 1) quantify cytosolic estrogen receptor (ER) concentrations in the lumbosacral spinal cord and 2) determine if there is a relationship between cytosolic ER concentrations and fluctuations in serum estradiol (SE2) levels during the estrous cycle. Lumbosacral spinal segments were removed from intact cycling rats during the morning of proestrus, the afternoon of proestrus, and the morning of estrus, metestrus and diestrus. Trunk blood was collected at euthanasia and SE2 levels were determined using radioimmunoassay. Cytosolic ER concentrations were measured using a dextran-charcoal coated tube method. Concentrations of cytosolic ERs were low during estrus and metestrus, increased during diestrus with maximum concentrations during the afternoon of proestrus. These changes in ER concentrations paralleled SE2 levels measured in intact cycling animals; i.e., during estrus SE2 levels were low, but began to rise during metestrus, diestrus, and during the morning of proestrus with a maximum peak increase during the afternoon of proestrus. These data indicate there are fluctuations of cytosolic ER concentrations during the estrous cycle and that these changes coincide with changing SE2 concentrations suggesting that ER content is influenced by SE2.     

The narA locus of Synechococcus sp. strain PCC 7942 consists of a cluster of molybdopterin biosynthesis genes

This study was conducted to analyze the roles of prolactin (PRL) and progesterone in the induction of luteal cell apoptosis and accumulation of macrophages in the regressing corpus luteum. We studied the number of apoptotic cells and macrophages in regressing corpora lutea in estrus 1) in cycling rats or after blocking PRL secretion with the dopaminergic agonist CB154, and 2) after blocking progesterone actions with the progesterone receptor antagonists RU-486 or ZK98299. Cells showing the morphological features characteristic of apoptosis contained fragmented DNA as indicated by in situ 3' end labeling. In cycling rats, a 100-fold increase in the number of apoptotic cells and a 4-fold increase in the number of macrophages was found from the evening (1600 h) of proestrus to the morning (1100 h) of estrus. Both increases were blocked by PRL suppression with CB154. Furthermore, blocking progesterone actions with progesterone receptor antagonists RU-486 or ZK98299 without affecting PRL secretion inhibited apoptosis but did not affect the accumulation of macrophages, whether treatment was started on the morning of metestrus (blocking diestrous and proestrous progesterone) or on proestrus (blocking only proestrous progesterone). Otherwise, exogenous progesterone was not effective in inducing apoptosis in the absence of PRL. These results indicate that both PRL and progesterone in proestrus are necessary for the induction of apoptosis in the regressing corpora lutea, whereas the accumulation of macrophages seemed to be dependent exclusively on the PRL surge.     

In vitro transfer rate of 14C from acetate-1-14C into ovarian steroids in the rat ovary during the estrous cycle and effects of LH and FSH

Fluctuations of ovarian biosynthetic activity and effects of exogenous LH and FSH on it during the estrous cycle were investigated by measuring in vitro transfer rates of 14C from 14C-1-acetate into progesterone (P), 20 alpha-hydroxy-pregn-4-en-3-one (20 alpha-OH-P) and estrogen (estradiol and estrone, E) in the ovarian homogenates from rats autopsied at 2 hour intervals. The transfer rate of 14C from 14C-1-acetate into P was lowest in the afternoon of estrus and increased from the morning of diestrus 1, making its peaks during the afternoon of diestrus 2 and in the midnight of proestrus. The transfer of 14C into 20 alpha-OH-P was high on the days of diestrus 2 and proestrus with its peak in the afternoon of the latter day. The maximum transfer of 14C into E in the afternoon of proestrus and a high rate in the morning of estrus with relatively low one in the midnight were observed. Exogenously injected LH (150 mug) or FSH (150 mug) was either stimulatory or inhiibitory to the transfer rates of 14C from 14C-1-acetate into ovarian steroids. During day time of diestrus 2 and midnight between proestrus and estrus, the transfer of 14C into P and 20 alpha-OH-P increased by LH, and during day time of proestrus and from the afternoon of estrus to the morning of diestrus 1 decreased. The transfer of 14C into E increased by LH from the afternoon of diestrus 2 to the morning of proestrus, and decreased during the afternoon of proestrus and from the afternoon of estrus to the morning of diestrus 2. Administration of FSH was also stimulatory or inhibitory. The 14C transfer into P and 20 alpha-OH-P increased by FSH from the afternoon of estrus to the morning of proestrus, but in the afternoon of proestrus they decreased. Transfer of 14C into E increased by FSH significantly on the days of diestrus 2 and proestrus, and slightly on the day of estrus, while it decreased in the afternoon of diestrus 1.     

Physiologic regulation of postovulatory neutrophil migration into vagina in mice by a C-X-C chemokine(s)

Leukocytes, particularly neutrophils, infiltrate into female genital organs after ovulation in both humans and mice. In mice, a female sexual cycle consists of 5 phases: proestrus, estrus, metestrus-1, metestrus-2, and diestrus. Ovulation occurs at estrus; at metestrus-2, a large number of neutrophils infiltrate into the vaginal epithelium accompanied by an increased neutrophil number in vaginal lavage fluid. Concomitantly, concentrations of a functional IL-8 homologue, murine macrophage inflammatory protein (MIP)-2, were increased significantly in vaginal lavage fluid at metestrus-2 as compared with other phases. On the contrary, MIP-2 was not detected in plasma during the whole course of a sexual cycle. Moreover, immunohistochemical analyses demonstrated that MIP-2 protein expression was prominent at the upper layer of the vaginal epithelium at metestrus-2, in contrast to a marginal staining in the vaginal epithelium at proestrus and estrus. These results suggest that a C-X-C chemokine, MIP-2, was produced physiologically in the vaginal epithelium in a sexual cycle-dependent manner. Furthermore, the administration of neutralizing anti-IL-8R homologue Abs at proestrus abrogated leukocyte infiltration into the vagina at metestrus. However, anti-MIP-2 Abs reduced leukocyte influx at metestrus by approximately 50%. Thus, a murine IL-8 homologue, MIP-2, and its related molecules physiologically regulate neutrophil migration into the vagina in a sexual cycle-dependent manner.     

Long-term observations of uterine contractions in nonpregnant dogs

Uterine contractile activity in nonpregnant conscious dogs was investigated based on 2- to 6-mo-long continuous recording by means of a chronically implanted force transducer. We found that nonpregnant uterine contractile activity could be classified into six major patterns: sporadic contractions, weak and strong tonic contractions, weak and strong phasic contractions, and phasic contraction bursts. The contractile patterns during proestrus and estrus were the most active, with strong phasic and tonic contractions and phasic contraction bursts. The phasic and tonic contractions were inhibited dose-dependently by a beta 2 adrenergic agonist, ritodrine, and reproduced by an alpha 2 adrenergic agonist, clonidine. In contrast, the cholinergic inhibitors atropine and hexamethonium did not affect the spontaneous occurrence of these contractions, although bethanechol evoked uterine contractions. Oxytocin and prostaglandin F2 alpha-induced contractions were phasic during estrus, whereas they showed tonic increases with phasic contractions during proestrus, diestrus, and anestrus, and these contractions did not resemble the spontaneous contractions. In conclusion, the nonpregnant uterus contracts continuously in harmony with the estrous cycle phases, and its contractile activity is enhanced by alpha adrenergic receptors and inhibited by beta 2 adrenergic receptors.     

Minocycline for the treatment of rheumatoid arthritis

This study examines the expression of the multi-functional cytokine, vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) in the rat uterus during early proestrus, proestrus, estrus and diestrus. Groups of ovariectomized or hypophysectomized rats served as endocrine controls. Expression of VPF/VEGF mRNA was 2-fold greater in uteri during proestrus and estrus than in other phases of the estrous cycle. In situ hybridization techniques indicated that VPF/VEGF mRNA expression was confined to the luminal epithelium during proestrus, but shifted to the stromal compartment during estrus. Ovariectomized, hypophysectomized or diestrus rats exhibited scattered localization of VPF/VEGF mRNA among glandular epithelium and endometrial stromal compartments. Although VPF/VEGF mRNA was expressed throughout the estrous cycle, but in different compartments of the endometrium depending on the stage of the estrous cycle, VPF/VEGF protein expression appears to be restricted to the epithelial compartment during proestrus and estrus. Results indicate that circulating levels of gonadal steroids and LH may be associated with the differential expression of VPF/VEGF mRNA and its translation activity in the endometrium during different stages of the estrous cycle.     

Influence of the estrous cycle on the sensitivity to catecholamines in right atria from rats submitted to foot-shock stress

We investigated the mechanisms of the alterations in sensitivity to catecholamines in right atria from female rats exhibiting regular 4-day estrous cycles after three foot-shock sessions at estrus, metestrus, and diestrus or at diestrus, proestrus, and estrus. Right atria from stressed rats sacrificed at diestrus showed subsensitivity to noradrenaline and adrenaline. After in vitro sympathetic denervation (38 microM 6-hydroxydopamine) plus inhibition of neuronal reuptake (0.1 microM desipramine) subsensitivity to noradrenaline was abolished, but it was again evident when extraneuronal uptake was also inhibited (10 microM phenoxybenzamine and 30 microM corticosterone). The same pretreatment abolished the subsensitivity to adrenaline. After addition of 1 microM butoxamine, a beta 2-adrenoceptor antagonist, the tissues from stressed rats were subsensitive to adrenaline. Right atria from stressed rats sacrificed at estrus did not show any alteration in sensitivity to catecholamines. We conclude that after foot-shock stress, right atria from female rats sacrificed at diestrus showed subsensitivity of the chronotropic response to catecholamines as a result of a conformational alteration of beta 1-adrenoceptors, simultaneously with an increase in beta 2-adrenoceptor-mediated response. The mechanisms seem to be similar to those which underlie stress-induced alterations in catecholamine sensitivity in right atria from male rats. However, during estrus there are some protective factors that prevent the effects of stress on right atria.     

Estradiol upregulates Bcl-2 expression in adult brain neurons

Bcl-2, a protein which negatively modulates apoptosis, is up-regulated by estrogen in several tissues. To determine the effect of estradiol on Bcl-2 in the adult brain, its immunoreactive distribution was examined in the hypothalamic arcuate nucleus of female rats under different endocrine conditions. The number of Bcl-2-immunoreactive neurons was significantly increased (p < 0.001) on the day of estrus compared with proestrus, diestrus and metestrus, was decreased by ovariectomy and showed a dose-response increase after estradiol administration to ovariectomized rats. Progesterone, when injected simultaneously with estradiol, reduced the effect of estradiol. These findings indicate that ovarian hormones regulate Bcl-2 in hypothalamic neurons and suggest that this protein may be involved in the neuroprotective effects of estrogen.     

Hypothalamus-pituitary-ovarian axis in cyclic rats lacking progesterone actions

Antagonizing diestrous progesterone actions in cyclic rats by s.c. injections of the antiprogesterone RU486 (2 mg twice a day from metestrus through proestrus) increased LH and decreased FSH basal serum concentrations. Ovariectomy at metestrus (0800 h) increased serum levels of both gonadotropins in controls and reversed the RU486-induced dissociation of basal gonadotropin secretion. RU486-dissociated gonadotropin secretion is also dependent upon LHRH, since treatment (s.c.) with 1 mg GnRH antagonist (ORG 30276) twice a day on metestrus and diestrus completely prevented both the RU486-induced increase in LH and the decrease in FSH serum concentrations. The LHRH content in the medial basal hypothalamus and median eminence increased on proestrous morning in RU486-treated rats. The LH pituitary response to an exogenous i.v. bolus of 25 ng LHRH (Peninsula 7201; Peninsula Laboratory, Inc., Merseyside, UK) at 1700 h on diestrus was enhanced in rats treated with RU486. No differences in pituitary FSH response were noted with respect to oil-injected rats. The pituitary content of both gonadotropins decreased in RU486-treated rats on proestrous morning. All these effects due to RU486 in cyclic rats were reversed by ovariectomy. Testosterone serum levels increased significantly from diestrus onward, and the estradiol concentration increased on proestrous morning in RU486-treated rats. Ovariectomy as well as LHRH antagonist treatment eliminated the effects of RU486 on ovarian steroid production. Moreover, antiestrogen tamoxifen treatment reversed RU486-dissociated gonadotropin secretion, while antiandrogen flutamide treatment had no effect. The results of this experiment have confirmed previous findings that RU486 treatment dissociates basal gonadotropin secretion in cyclic rats. In addition, the present results show that: (1) this effect of RU486 is not due to a direct effect of this compound or to the blockade of progesterone action at a central level; (2) the effect of RU486 on pituitary gonadotropin secretion depends on ovarian substances other than progesterone and LHRH, since it is reversed by ovariectomy and completely abolished by LHRH antagonist treatment; (3) the reduction in FSH serum levels in rats treated with RU486 seems to be exerted by inhibin and estradiol at the pituitary level by reducing FSH synthesis and secretion; and (4) the hypersecretion of LH in rats treated with RU486, as compared to that resulting from ovariectomy, seems to be the consequence of, first, a lack of progesterone inhibitory action on LH secretion, and, second, an inappropriate feedback system involving increased hypothalamic LHRH activity and pituitary sensitivity to LHRH of moderately high levels of estradiol in the presence of abnormally high levels of testosterone.     

Influence of the estrous cycle on the norepinephrine-induced contraction of rat aorta: relationship to vascular prostanoids biosynthesis

Since ovarian sex steroids (estradiol and progesterone) may affect both blood pressure and prostanoids synthesis, and because prostaglandin-E2 (PGE2) and prostacyclin (PGI2) can modulate the vascular action of pressor hormones, we investigated the vascular reactivity to norepinephrine during the estrous cycle of the rat. In addition, we determined the vascular biosynthesis of PGE2 and 6-keto-PGF1 alpha (the stable metabolite of PGI2) at different stages of the estrous cycle. Cumulative dose-response curves were obtained by a stepwise increase in the concentration of norepinephrine. The contraction of thoracic aortic rings induced by norepinephrine did not change significantly between estrus, metestrus and diestrus. However, aortic rings obtained on proestrus showed a significant reduction in the maximal contraction (Emax) induced by norepinephrine (p < 0.001). In addition, we found significant increases in vascular synthesis of PGE2 and PGI2 on proestrus (p < 0.001). These results indicate that vascular reactivity and vascular prostanoids synthesis are influenced by the hormonal changes occurring during the estrous cycle of normal female rats. It is possible that prostanoids generated locally may play an important role in the regulation of vasomotor tone in the systemic vascular bed throughout the estrous cycle.     

Changes in visceral pain reactivity as a function of estrous cycle in female rats with artificial ureteral calculosis

This study examined estrous differences in the characteristics of behavioral crises of visceral pain in female rats video-taped throughout a 4-day period after implantation of an artificial stone in one ureter. All animals continued to have a regular cycle after ureteral surgery. In the recording period, the percentage of time spent in crises was significantly higher during metestrus/diestrus (M/D) than during proestrus/estrus (P/E) (P < 0.001, chi2-test). Mean duration and complexity of crises were slightly higher in M/D than in P/E, but the difference was not significant. The results in this animal model show an enhancement of ureteral pain sensitivity in M/D, a finding in line with the clinical observation, in fertile women with urinary calculosis, of a greater incidence of colics in the perimenstrual period (equivalent to M/D in rats).     

Developmental changes in the hypoxic response of the hypoglossus respiratory motor output in vitro

The transverse brain stem slice of mice containing the pre-B?tzinger complex (PBC), a region essential for respiratory rhythm generation in vitro, was used to study developmental changes of the response of the in vitro respiratory network to severe hypoxia (anoxia). This preparation generates, at different postnatal stages [postnatal day (P)0-22], spontaneous rhythmic activity in hypoglossal (XII) rootlets that are known to occur in synchrony with periodic bursts of neurons in the PBC. It is assumed that this rhythmic activity reflects respiratory rhythmic activity. At all examined stages anoxia led to a biphasic response: the frequency of rhythmic XII activity initially increased ("primary augmentation") and then decreased ("secondary depression"). In neonates (P0-7), anoxia did not significantly affect the amplitude of integrated XII bursts. Secondary depression never led to a cessation of rhythmic activity. In mice older than P7, augmentation was accompanied by a significant increase in the amplitude of XII bursts. A significant decrease of the amplitude of XII bursts occurred during secondary depression. This depression led always to cessation of rhythmic activity in XII rootlets. The anoxia-induced response of the respiratory rhythmic XII motor output is biphasic and changes during development in a similar way to the in vivo respiratory network. Whether this biphasic response is due to a biphasic response of the respiratory rhythm generator and/or to a biphasic modulation of the XII motor nucleus remains unresolved and needs further cellular analysis. We propose that the transverse slice is a useful model system for examination of the mechanisms underlying the hypoxic response.     

The protective effect of moderate alcohol consumption on ischemic stroke

Experiments were designed to investigate the influence of estrous cycle and gender of the rat on the effects of a gamma-aminobutyric acid type A (GABA(A)) receptor active neurosteroid, 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone), the benzodiazepine, triazolam, and a GABA(A) receptor antagonistic neurosteroid, delta5-androsten-3beta-ol-17-one sulfate (dehydroepiandrosterone sulfate), on food intake and elevated plus-maze learning behaviors. Allopregnanolone (0.25 mg/kg, s.c.) and triazolam (0.25 mg/kg, i.p.) produced a hyperphagic effect, while dehydroepiandrosterone sulfate (5 mg/kg, s.c.) elicited an anorectic effect. However, allopregnanolone was more potent in diestrous females, whereas triazolam exhibited significantly higher hyperphagic potency in estrus females. The extent of anorexia following dehydroepiandrosterone sulfate was alike in male and female rats. The triazolam- and allopregnanolone-induced hyperphagic effect was blocked by bicuculline (1 mg/kg, i.p.), a selective GABA(A) receptor antagonist. In contrast to triazolam, the hyperphagic effect of allopregnanolone was insensitive to flumazenil (5 mg/kg, i.p.), a benzodiazepine antagonist. Vehicle-treated diestrous rats displayed moderately higher latencies in the elevated plus-maze learning task than estrus or proestrus females. Although allopregnanolone and triazolam elicited equipotent learning deficits in plus-maze learning in male and female rats, the magnitude of impairment-induced by triazolam was significantly higher in diestrous females than proestrus females. Dehydroepiandrosterone sulfate enhanced memory performance only in male rats. Although the use of the elevated plus-maze as a learning paradigm with benzodiazepines and neurosteroids may be sensitive to changes in anxiety, the differential data suggest that neurosteroid-induced effects are at least partly specific to learning behavior. These results confirm the role of estrous cycle and sex of rats in modifying the potency of neurosteroids and benzodiazepines on food consumption and learning and memory processes.     

Regulation of the preovulatory gonadotropin surge by endogenous steroids

Estradiol secreted by growing ovarian follicle(s) has been considered classically to be the neural trigger for the preovulatory surge of gonadotropins. The observation that the estradiol-induced gonadotropin surge in ovariectomized rats is of lesser magnitude and duration than that found in the cycling rat at proestrus has resulted in a search for other steroid regulators. Progesterone is a major regulator of the preovulatory gonadotropin surge. It can only act in the presence of an estrogen background, which is necessary for the synthesis of progesterone receptors. In the estrogen-primed ovariectomized rat, progesterone is able to initiate and enhance the gonadotropin surge to the magnitude observed on the day of proestrus and limit it to 1 day. The physiological role of progresterone in the induction of the preovulatory gonadotropin surge has been demonstrated by the attenuation of the progesterone-induced surge and the endogenous proestrus surge by progesterone receptor antagonist RU486 and the progesterone synthesis inhibitor trilostane. The promoter region of the follicle-stimulating hormone (FHS)-beta gene contains multiple progesterone response elements and progesterone brings about FSH release as well. The reduction of progesterone in the 5 alpha-position appears to be important for the regulation of progesterone secretion. Corticosteroids appear to play a significant role in the secondary FSH surge on late proestrus and early estrus.     

Epileptic discharge of cortical, subcortical and spinal neurons in penicillin induced experimental epilepsy

The sensitivity and electrophysiological patterns of paroxysmal activity induced in different brain structures by topical application of penicillin-G were evaluated in the rat. Recordings were carried out in five groups of animals, in telencephalon, diencephalon, mesencephalon, rombencephalon and spinal cords. The following analysis were carried out: frequency distribution histograms, latency and time course duration of paroxysmal activity, duration and amplitude of epileptic bursts. The results obtained showed that the nervous structures tested with penicillin-G had a different epileptogenic sensitivity and response pattern which significantly changed along the cerebral cortex-spinal cord axis. The highest epileptic sensitivity was observed in somatosensory cortex (SI) at 500-600 microns depth; in the other cortical layers, a significant lenghtening in latency was observed. Among the other structures, the spinal cord seemed to be the most sensitive target to the epileptogenic action of penicillin-G, whereas in the remaining structures, sensitivity significantly decreased in rostro-caudal direction. As far as the features of the paroxysmal activity are concerned, significant differences among tested structures were observed. In particular, within the SI cortex, the main differences were represented by the gradual increase in burst frequency and voltage from the surface to the IVth layer and by their subsequent decrease in deeper layers (V-VI). In the diencephalon, the paroxysmal activity was similar to that observed in more superficial and deeper cortical layers even though epileptic bursts showed a lower amplitude. Mesencephalon and rombencephalon displayed a paroxysmal activity with a distinctive feature, characterized by long lasting bursts of low amplitude, although bulbar outbursts showed a shorter duration than the mesencephalic ones. In the spinal cord, the epileptiform activity displayed a different paroxysmal pattern, characterized by the longest duration and the highest amplitude. The different sensitivities of the investigated brain structures to penicillin-G and the characteristics of the induced paroxysmal activity have been extensively discussed.     

Occurrence of deoxyribonucleic acid fragmentation during prolactin-induced structural luteolysis in cycling rats

We determined whether fragmentation of genomic DNA, one of the hallmarks of apoptosis, occurs during structural luteolysis in cycling rats. Corpora lutea (CL) were collected from rats at each estrous cycle stage (1800 h), and fragmented DNA was extracted. Only CL from rats at the proestrous stage showed distinct DNA fragmentation. To determine the period of occurrence of DNA fragmentation, CL were collected at several points between 1200 h on the day of proestrus and 0600 h on the day of estrus. Distinct DNA fragmentation was observed from 1800 h (proestrus) to 2400 h (proestrus), and the extent was significantly lower at 0600 h (estrus). It is known that prolactin (PRL) induces structural luteolysis in rats. To examine the role of PRL in luteal DNA fragmentation, 2-bromo-alpha-ergocryptine (BE) was used to suppress the PRL surge on the day of proestrus. CL collected at 1800 h from BE-treated rats did not show distinct DNA fragmentation, and PRL injection offset the effect of BE. Histochemical analysis with a 3'-end labeling technique confirmed the occurrence of DNA fragmentation in luteal tissue. These results suggest that apoptotic cell death occurs during PRL-induced structural luteolysis.     

A single dose of mifepristone induces ovulation in pseudopregnant rats

We used mifepristone (M) to evaluate the role of progesterone in maintaining pseudopregnancy. Cycling rats were made pseudopregnant (psp) by cervico-vaginal stimulation (CVS) on the day of estrus (day 0) and received 10 mg/kg M or vehicle (control groups) on day 3. Blood samples were taken at 06.00 h on days 4, 6 or 7 or at 18.00 h on days 3, 4, 6 or 10. M induced proestrus 2 days later (day 5), estrus on day 6, and a second prolonged diestrus afterwards. Prolactin and progesterone levels were similar in the control and M treated groups excepting on day 6, when both were reduced in the M-treated animals, and these rats were in estrus, suggesting a temporary impairment of luteal function. To demonstrate activated corpora lutea the endometrium was scratched on the fourth day of the first or second diestrus in additional control and M-treated groups. The deciduomal response was seen in the control and M groups after scratching the endometrium on day 4 of the first or second diestrus, respectively, but M blocked the deciduomal response in the first diestrus. Ovulation was confirmed by finding that 66.7% of the M-treated rats showed ova in the Fallopian tubes on the M-induced estrus and 4 out of 10 of the M rats placed with males on the M-induced proestrus showed spermatozoa in the vaginal smears. Half of these became pregnant, delivering 2 pups each. The results show that M can induce ovulation in psp rats, demonstrating that the anovulation observed after CVS is dependent on progesterone, yet luteal function persists after M in pseudopregnancy. Progesterone may act either by suppressing LH secretion or by permitting prolactin secretion, or both. Moreover, progesterone is required to maintain endometrial responsiveness.