Regulation of oxytocin, oestradiol and progesterone receptor concentrations in different uterine regions by oestradiol, progesterone and oxytocin in ovariectomized ewes

The regulation of oxytocin, oestradiol and progesterone receptors in different uterine cell types was studied in ovariectomized ewes. Animals were pretreated with a progestogen sponge for 10 days followed by 2 days of high-dose oestradiol to simulate oestrus. They then received either low-dose oestradiol (Group E), low-dose oestradiol plus progesterone (Group P) or low-dose oestradiol, progesterone and oxytocin (via osmotic minipump; Group OT). Animals (three to six per time-point) were killed following ovariectomy (Group OVX), at oestrus (Group O) or following 8, 10, 12 or 14 days of E, P or OT treatment. In a final group, oxytocin was withdrawn on day 12 and ewes were killed on day 14 (Group OTW). Oxytocin receptor concentrations and localization in the endometrium and myometrium were measured by radioreceptor assay, in situ hybridization and autoradiography with the iodinated oxytocin receptor antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH2(9)]-vasotocin. Oestradiol and progesterone receptors were localized by immunocytochemistry. Oxytocin receptors were present in the luminal epithelium and superficial glands of ovariectomized ewes. In Group O, endometrial oxytocin receptor concentrations were high (1346 +/- 379 fmol [3H]oxytocin bound mg protein-1) and receptors were also located in the deep glands and caruncular stroma in a pattern resembling that found at natural oestrus. Continuing low-dose oestradiol was unable to sustain high endometrial oxytocin receptor concentrations with values decreasing significantly to 140 +/- 20 fmol mg protein-1 (P < 0.01), localized to the luminal epithelium and caruncular stroma but not the glands. Progesterone treatment initially abolished all oxytocin receptors with none present on days 8 or 10. They reappeared in the luminal epithelium only between days 12 and 14 to give an overall concentration of 306 +/- 50 fmol mg protein-1. Oxytocin treatment caused a small increase in oxytocin receptor concentration in the luminal epithelium on days 8 and 10 (20 +/- 4 in Group P and 107 +/- 35 fmol mg protein-1 in Group OT, P < 0.01) but the rise on day 14 was not affected (267 +/- 82 in Group OT and 411 +/- 120 fmol mg protein-1 in Group OTW). In contrast, oestradiol treatment was able to sustain myometrial oxytocin receptors (635 +/- 277 fmol mg protein-1 in Group O and 255 +/- 36 in Group E) and there was no increase over time in Groups P, OT and OTW with values of 61 +/- 18, 88 +/- 53 and 114 +/- 76 fmol mg protein-1 respectively (combined values for days 8-14). Oestradiol receptor concentrations were high in all uterine regions in Group O. This pattern and concentration was maintained in Group E. In all progesterone-treated ewes, oestradiol receptor concentrations were lower in all regions at all time-points. The only time-related change occurred in the luminal epithelium in which oestradiol receptors were undetectable on day 8 but developed by day 10 of progesterone treatment. Progesterone receptors were present at moderate concentrations in the deep glands, caruncular stroma, deep stroma and myometrium in Group O. Oestradiol increased progesterone receptors in the luminal epithelium, superficial glands, deep stroma and myometrium. Progesterone caused the loss of its own receptor from the luminal epithelium and superficial glands and decreased its receptor concentration in the deep stroma and myometrium at all time-points. There was a time-related loss of progesterone receptors from the deep glands of progesterone-treated ewes between days 8 and 14. These results show differences in the regulation of receptors between uterine regions. In particular loss of the negative inhibition by progesterone on the oxytocin receptor by day 14 occurred only in the luminal epithelium, but is unlikely to be a direct effect of progesterone as no progesterone receptors were present on luminal epithelial cells between days 8 and 14.     

Changes in the secretion of ovarian steroid and pituitary luteinizing hormone in the peri-ovulatory period in the ewe: the effect of progesterone

The secretion rates of oestradiol, androstenedione and progesterone and the peripheral plasma concentration of LH were measured in 12 ewes with ovarian autotransplants before and after luteal regression induced by a single intramuscular injection of a synthetic prostaglandin (PG) analogue, 16-aryloxyprostaglandin F 2alpha (I.C.I. 80996). Luteal regression was followed by a fourfold rise in the basal concentration of LH and increased secretion of oestradiol. In five out of six ewes there was a discharge of LH with the peak occurring 36--78 h after the injection of the PG analogue. The secretion of oestradiol declined from 3-68 +/- 1-08 to 0-33 +/- 0-6 (S.E.M.) ng/min in the 24 h following the LH peak (P less than 0-001). In the remaining six ewes in which progesterone was implanted subcutaneously 24 h after the injection of PG analogue, follicular development was suppressed as indicated by the low secretion of oestradiol and androstenedione. The basal concentration of LH fell to values similar to those observed during the luteal phase after the implant of progesterone. The secretion of androstenedione followed a similar pattern to that of oestradiol in those ewes which showed presumptive evidence of ovulation. These results suggest that progesterone reinforces the negative feedback effects of oestrogen in the ewe.     

Uterine secretion of prostaglandin F2 alpha in the ewe: regulation at the cellular level by ovarian hormones and the conceptus

Changes in the ability of the uterus to secrete prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin may play a critical role in determining when endogenous secretion of PGF2 alpha begins. The cellular mechanisms that regulate uterine secretion of PGF2 alpha in response to oxytocin have not been completely defined. Several intracellular components that may contribute to this regulation have been studied, including phospholipase C (PLC), prostaglandin H endoperoxide synthase (PGS) and receptors for oxytocin. All of these components change during the oestrous cycle and are associated with the development of uterine secretory responsiveness to oxytocin. Progesterone appears to play the principal role in regulating oxytocin receptors, PLC and PGS. The conceptus appears to suppress the increase in receptors for oxytocin and PLC activity that typically occurs around the time of luteal regression.     

Effect of pulsatile oxytocin administration to the pregnant ewe in the last third of gestation on fetal ACTH and cortisol response to acute hypoxemia

OBJECTIVE: The aim of this study was to examine the effect of increased myometrial contractility throughout the last third of pregnancy on the ovine fetal response to short-term hypoxemia. METHODS: Oxytocin (600 microU/kg/minute, n = 5) or saline (n = 7) was infused for 5 minutes every 20 minutes into the maternal jugular vein starting at 95-99 days of gestation and continuing throughout the last third of gestation. Fetuses were subjected to a hypoxemic challenge (1 hour) at 131 days of gestation while fetal plasma ACTH and cortisol levels and nuchal muscle electromyogram activity were monitored. RESULTS: The fetal plasma ACTH concentration before and during the hypoxemic challenge was similar in the control and oxytocin groups. The fetal plasma cortisol concentration in the oxytocin group was significantly lower before and during the hypoxemia than in the controls. During hypoxemia, fetal nuchal muscle activity was significantly reduced only in the control group. CONCLUSION: Increased myometrial contracture frequency throughout the last third of pregnancy alters both the neuroendocrine and behavioral responses of fetal sheep to short-term hypoxemia.     

Effect of an ovulatory dose of luteinizing hormone on the concentration of oestrone, oestradiol and progesterone in the rabbit ovarian follicles

This study was done to determine the effect of an ovulatory dose of LH on the concentration of oestrone, oestradiol and progesterone in the follicular tissue and in follicular fluid of ovaries of sexually mature female rabbits. Eight animals were sacrificed without treatment while others (4 to a group) were sacrificed at 1, 3, 4, 6, 8 and 10 h after administration of LH (50 mug). In each animal follicles from both ovaries were pooled and the follicular tissue was separated from the fluid. Determination of oestrone, oestradiol and progesterone was done by radioimmunoassay separately in the follicular tissue and in fluid. One hour after LH treatment oestrogen levels were found elevated, as compared to the control, in the fluid but not in the tissue. Thereafter oestrogen levels declined and reached levels much below control at times nearing ovulation. On the other hand, progesterone levels were elevated over the control in both the tissue and fluid at 1 and 3 h. The tissue progesterone levels were, however, below control at and after 6 h. The sustained high concentrations of tissue progesterone in the earlier period after LH stimulation could play a role in the chain of events leading to follicular rupture.     

Priming effect of exogenous oestradiol on luteinizing hormone secretion in prepubertal lambs

Electrophysiological exploration of the facial nerve requires different tests to differetciate the importance of the block, denervation and canal conduction. We must answer five questions: 1) Assessing the degree and the phase of the nerve lesion, 2) Deciding on the advisability of a facial decompression in the early stage of the palsy, 3) Evaluating the prognosis, 4) Choosing the best therapeutic approach, 5) Detecting facial hyperkinesis in an infraclinic period. In order to answer these questions, we select the following methods: 1) Quantified Electroneuronography should be applied as early as the 2nd day after onset, repeated on the 7th and 10th days. Unfortunately this is not always possible for practical reasons. In any case a minimum of two investigations should be performed during the 12 first days. 2) We add Computer EMG in order to control the evolution of the blocked fibers with regard to denervated fibers. 3) Blink reflex and Stapedius reflex are investigated from the 3rd day. After the acute phase of the palsy, recovery is detected by the reappearance of the blink and stapedius reflexes and the evolution of the computed EMG. These tests are sufficient for answering the five questions mentioned above without discomfort for the patient.     

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)     

Morphine inhibits nocturnal oxytocin secretion and uterine contractions in the pregnant baboon

Morphine is a potent inhibitor of nocturnal uterine contractions (UCs) in the pregnant baboon, and these contractions are known to be induced by oxytocin (OT). The purpose of this study was to determine the mode of action of morphine in inhibiting nocturnal UCs by examining the effect of morphine on OT secretion, OT clearance, and uterine responsiveness to OT. A tethered pregnant baboon model during the last third of gestation was used for these experiments. In study 1, the effects of morphine or control saline on OT release and on spontaneous nocturnal UCs were examined. Study 2 determined the effects of morphine or control saline on the pharmacokinetics of OT after a bolus injection of OT. To exclude/include direct opiate effects on UCs, study 3 examined the responsiveness of the uterus to exogenous OT after morphine or control saline administration. Plasma OT levels were analyzed by RIA after extraction. UCs were assessed by frequency, amplitude, duration, and area under the curve. During nocturnal UCs, morphine, but not saline, administration resulted in the precipitous suppression of integrated OT levels (p < 0.05) to 42% of pretreatment values at 0-15 min postinjection and 17% at 30-45 min. Simultaneously, UCs were significantly suppressed (p < 0.05) by 75% at the 30- to 45-min interval. By 1 h, 5 of 7 animals showed no UCs. In study 2, morphine consistently increased the metabolic clearance rate (MCR) of OT in all trials (p < 0.05), although the magnitude of this effect was small (median 9%). Finally, study 3 demonstrated that myometrial responsiveness to the challenge of exogenous OT was not depressed by opiate administration (p > 0.05). To summarize, the decrease in nocturnal UCs after morphine is primarily due to an inhibition of OT release, and perhaps, but to a much lesser extent, an increase in OT MCR. There was no evidence of a direct tocolytic effect of morphine on the uterus. In conclusion, opioids such as morphine are potent inhibitors of nocturnal UCs and act by suppressing OT release in the pregnant baboon.     

Effects of oxytocin on in vitro ovarian contractility during the estrous cycle of the rat

Necrotizing skin lesions developed in a man with chronic ulcerative colitis. No evidence of intrinsic disease of medium or small-sized vessels was found. A circulating cryofibrinogen was thought to be responsible for in situ thrombosis leading to skin infarctions. Sodium warfarin in a daily dose of 2.5 to 5 mg appears to have thwarted progression of developing lesions and the occurrence of new ones.     

The influence of the maternal heart rate on the uterine artery pulsatility index in the pregnant ewe

We investigated the influence of the maternal heart rate on the uterine artery pulsatility index in pregnant ewes. We used an external pacemaker to alter the heart rate of 5 pregnant ewes at 16-17 weeks of pregnancy and examined the effect of changes in the maternal heart rate on the uterine artery flow velocity waveforms and the pulsatility index, as determined by Doppler velocimetry. The uterine artery pulsatility index showed a significant negative correlation with the maternal heart rate. There were no significant changes in other hemodynamic parameters. The maternal heart rate had a significant influence on the uterine artery pulsatility index.     

The 24-hour rhythm of oxytocin and beta-endorphin secretion in human pregnancy

OBJECTIVE: Animal work suggests that maternal oxytocin secretion is influenced by the secretion of endogenous opioids in pregnancy. Spontaneous labour and pre-labour uterine activity follow a 24-hour rhythm the origin of which has not been explained but may be related to diurnal changes in oxytocin secretion. This study was performed to document the changes over a 24-hour period in maternal oxytocin and beta-endorphin secretion. DESIGN: A 4-hourly blood profile was undertaken for a 24-hour period. PATIENTS: Sixteen women with singleton pregnancies of more than 36 weeks gestation and 10 women with pregnancies in the mid trimester were studied. MEASUREMENTS: Blood was sampled 4-hourly for 24 hours beginning at 1200 h. Oxytocin was measured in all patients and beta-endorphin-like immunoreactivity was measured in 15 patients. RESULTS: A simple index was defined for comparing night-time levels to daytime levels for both oxytocin and beta-endorphin. In all cases more than 36 weeks gestation the index was positive for oxytocin (night-time levels were higher) and in all cases the index was negative for beta-endorphin (night-time levels were lower). In the mid trimester women all values of the index for oxytocin were positive but in the beta-endorphin group equal numbers demonstrated a positive or a negative index. CONCLUSIONS: Reciprocal 24-hour rhythms were demonstrated between oxytocin and beta-endorphin; however, it is not clear whether this relationship is causal.     

Does a short loop feedback mechanism for the control of luteinizing hormone secretion exist in the ewe?

It is not known whether a short loop feedback mechanism for the regulation of LH exists in sheep. This study on ovariectomized ewes investigated whether a bolus injection (10, 1, and 0.1 microg LH or 1 microg BSA; n 4) or a 3-h continuous infusion of exogenous LH (100 or 1 ng/min; n = 7) into the third ventricle through a permanent indwelling cannula could influence the activity of the GnRH pulse generator, as determined by measurement of endogenous LH secretion. To assess the potential for involvement in a LH short loop feedback system and to estimate the level of LH in the hypothalamic milieu, the concentrations of LH in the peripheral circulation, portal circulation, and third ventricle were measured during an estradiol-induced preovulatory LH surge (n = 4). Neither the bolus nor continuous administration of LH into the third ventricle had any effect on the mean interpulse interval, nadir, pulse amplitude, or circulating level of systemic LH. Furthermore, despite portal LH concentrations being more than 20-fold higher than jugular LH concentrations, LH levels in third ventricular cerebrospinal fluid remained barely detectable and did not reflect dynamic secretory events in the peripheral or hypothalamo-hypophyseal portal blood. These data demonstrate that in ewes, little pituitary LH reaches the third ventricle, and the small amount that does is unable to affect peripheral gonadotropin release. Our study suggests, therefore, that a short loop feedback system for LH does not exist in the ewe.     

Effect of 'unstirred' water layer in the intestine on the rate and extent of absorption after oral administration

The presence of an aqueous diffusion layer or 'unstirred' water layer adjacent to the intestinal membrane has long been regarded as a potential barrier for intestinal absorption of compounds. Theoretical analyses were performed in the present study to quantitatively determine the effect of this layer on the rate and extent of absorption of passively absorbed compounds with different membrane absorption half-lives (10 to 300 min) in humans, dogs, rabbits, rats and mice. Diffusion half-lives across this (40 microns thick) layer were estimated to be 5.8, 2.5, 1.1, 0.65 and 0.32 min, respectively, in the distended intestine of the above five species. These half-lives are reduced by about 5-fold when the intestine is about 80% 'flat' in fasting state. The results of extensive analysis indicate that the presence of such a layer is generally expected to have a relatively mild or insignificant effect on the rate of absorption and an insignificant effect on the extent of absorption. The study also indicates that an aqueous layer of 708 microns has practically no effect on the extent of absorption of progesterone, a highly lipophilic compound, in rats. For prediction of or correlation with the fraction of oral dose absorbed after oral administration, the present study indicates that use of apparent or effective permeability rather than unbiased or true wall (membrane) permeability, as advocated earlier by others, should generally suffice.     

Effect of cooling rate and alloying on the

The pearlitic hardenability of a high-purity Fe-0.8 pct C alloy and zone-refined iron binary alloys containing Mn, Ni, Si, Mo, or Co was studied by means of hot-stage microscopy. The binary alloys were carburized in a gradient furnace to produce eutectoid compositions, thus eliminating proeutectoid phases. A special technique based on hot-stage microscopy was used to study the effect of cooling rate (10°F/min to 25,000°F/min) on the transformation of austenite and provided data for the construction of continuous cooling-transformation diagrams. From these diagrams critical cooling rates were obtained for hardenability calculations. It was found that molybdenum is the most effective element, followed by Si, Ni, Co, and Mn, in suppressing the pearlite transformation,i.e., in increasing the hardenability of the alloys studied. The alloying additions were grouped into two classes according to their effect on hardenability: α-stabilizers (Mo and Si) and γ-stabilizers (Ni, Co, Mn), with the α-stabilizers being the more effective in improving hardenability. This paper is based on a presentation made at a symposium on “Hardenability” held at the Cleveland Meeting of The Metallurgical Society of AIME, October 17, 1972, under the sponsorship of the IMD Heat Treatment Committee.     

Plasma concentrations of ethynyl oestradiol and norethindrone after oral administration to women

Rapid vasicular resistance adjustments in the brain and in the circle of Willis have been continuously measured and enhanced by signal averaging methods. Naftidrofuryl, a drug chemically similar to local anesthetics and to beta adrenergic blocking agents, increases local CBF by reducing resistance in brain and in extracerebral supply arteries. It has also been reported to affect brain metabolism. Other similar drugs merit study for potential effects on CBF and brain metabolism which may be useful in treatment.