Effects of progesterone on expression of messenger RNA encoding oxytocin-neurophysin, oxytocin receptor and prostaglandin G/H synthase-1 and -2 during the early oestrous cycle in the ovine corpus luteum

This study was conducted to determine whether early progesterone treatment plays a role in the regulation of messenger RNA (mRNA) expression for oxytocin-neurophysin, oxytocin receptor, prostaglandin G/H synthase (PGHS)-1 and PGHS-2 in the ovine corpus luteum. The expression of ovarian oxytocin, oxytocin receptor, PGHS-1 and PGHS-2 mRNA was investigated in control, progesterone- or RU486-treated ewes. Fifteen ewes were randomly assigned to three groups to receive intramuscular injections of progesterone (12.5 mg; n = 5), RU486, (2.5 mg kg(-1) bodyweight; n = 4) or corn oil (1 mL; n = 6) twice daily from Day 1 to Day 3 post oestrus. On the morning of Day 4 post oestrus, the corpora lutea were collected and analysed for oxytocin-neurophysin mRNA by Northern blot using a labelled cDNA probe, and for the expressions of the oxytocin receptor, PGHS-1 and PGHS-2 mRNA using the reverse transcription polymerase chain reaction. Administration of progesterone or suppression of progesterone activity with RU486 did not affect expression of oxytocin-neurophysin mRNA (P>0.05). Pretreatment of the ewes with progesterone resulted in the enhancement of luteal oxytocin receptor mRNA expression and suppression of PGHS-1 and PGHS-2 mRNA (P<0.001). These results indicate that early progesterone treatment does not control the expression of oxytocin-neurophysin mRNA in the ovine ovary but may be involved in the regulation of ovarian oxytocin receptor and PGHS expression. It is proposed, on the basis of these results, that progesterone may play a role in premature corpus luteum regression through an intra-ovarian mechanism involving the induction of ovarian oxytocin receptor mRNA expression.

Feto-placental hypoxemia regulates the release of fetal activin A and prostaglandin E(2)

The evaluation of the role of critical hypoxia in unexplained fetal death in utero has been hampered by the lack of a physiological marker. Here we report the novel observation that feto-placental hypoxemia is an acute trigger for increased activin secretion from the feto-placental unit in late pregnancy. Hypoxemia was induced in chronically cannulated late pregnant fetal sheep by restricting blood flow through the maternal uterine arteries. Using maternal and fetal blood samples and amniotic fluid obtained via chronically implanted catheters, fetal blood gas parameters, plasma and amniotic fluid concentrations of activin A, prostaglandin (PG) E(2) and PGFM, the circulating metabolite of PGF(2alpha), were determined before, during and after a ten hour period of fetal hypoxemia. Hypoxemia acutely increased activin A and PGE(2) levels in both amniotic fluid and the fetal circulation with values rapidly returning to baseline with normoxemia. PGFM also increased in both compartments with a relatively delayed time frame compared to that of activin A and PGE(2). The increase in activin A and PGE(2) induced by hypoxemia may be a mechanism to regulate feto-placental blood flow during fetal compromise and also offers the possibility that activin A represents a useful marker of feto-placental hypoxemia.

Follicular development in cryopreserved Common Wombat ovarian tissue xenografted to Nude rats

The Northern Hairy-nosed Wombat (Lasiorhinus krefftii) is a highly endangered marsupial species and every possible option for sustaining the species needs to be explored. One important approach may be the development of assisted reproductive technologies in the non-endangered Common Wombat (Vombatus ursinus) and Southern Hairy-nosed Wombat (Lasiorhinus latifrons) for application in breeding the Northern Hairy-nosed Wombat. In this study, it was examined whether cryopreserved Wombat ovarian tissue would develop following xenografting to immunologically deficient rats. Ovarian tissue was collected from Common Wombats (n = 3) and cryopreserved as small cortical pieces. After thawing the cortical pieces were grafted underneath the kidney capsule of Nude rats (n = 16). The grafts were recovered at 2, 4, and 10 weeks after transplantation and their gross and histological appearance investigated. Two weeks after grafting (n = 2), the tissue was revascularized and healthy primordial follicles were present. At week 4 (n = 2), some follicular development was present. At week 10, six rats received human chorionic gonadotrophin (hCG) to trigger follicle and oocyte maturation while another six rats were not given any treatment. The administration of hCG did not induce preovulatory follicles and oocyte maturation although type 5 follicles were present in ovarian tissue collected 10 weeks posttransplantation in both treated and untreated groups. This study demonstrates for the first time that Wombat ovarian tissue can survive and function when grafted into immunocompromized rats and that Wombat ovarian follicles can be recruited to growth and development in an ovarian xenograft. This model system has the potential to produce mature oocytes from endangered species for use in assisted reproductive technologies such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and mature oocytes from non-endangered species for nuclear transfer which may be necessary for the preservation of critically endangered species.

Inhibition of premature labor in sheep by a combined treatment of nimesulide, a prostaglandin synthase type 2 inhibitor, and atosiban, an oxytocin receptor antagonist

OBJECTIVE

The aim of this study was to compare the effects of the selective prostaglandin synthase type 2 inhibitor nimesulide, alone or in combination with the oxytocin receptor antagonist atosiban, on the progression of glucocorticoid-induced premature labor in sheep. Effects on circulating maternal and fetal prostaglandin concentrations and on fetal well-being were also examined.

STUDY DESIGN

Premature labor was induced in ewes with long-term catheterized fetuses by infusion of dexamethasone (1 mg/d) starting at 138 +/- 1 days' gestation. Ewes also received an infusion of either nimesulide and atosiban (20.0 and 4.12 mg/kg per day, respectively; n = 5), nimesulide alone (20.0 mg/kg per day; n = 5), or vehicle only (n = 9). Plasma 13,14-dihydro-15-keto-prostaglandin F(2)(alpha) and prostaglandin E(2) concentrations were measured before and during infusions in plasma samples obtained from the maternal and fetal carotid arteries and the utero-ovarian vein.

RESULTS

No fetuses from ewes treated with nimesulide and atosiban were delivered during treatment. These animals were killed electively 98.0 +/- 6.8 hours after the commencement of dexamethasone induction. This was significantly longer than the delivery times for those ewes treated with nimesulide alone (71.2 +/- 3.9 hours; n = 5) and for vehicle-treated ewes (51.4 +/- 1.7 hours; n = 9). Both maternal and fetal plasma 13, 14-dihydro-15-keto-prostaglandin F(2alpha) and prostaglandin E(2) concentrations in nimesulide and atosiban-treated ewes and in nimesulide-treated ewes decreased during treatment. In contrast, vehicle-treated ewes showed a significant increase in maternal and fetal plasma 13,14-dihydro-15-keto-prostaglandin F(2alpha) and prostaglandin E(2) concentrations during dexamethasone induction. Uterine electromyographic activity observed in nimesulide and atosiban-treated ewes was significantly suppressed with respect to activities in both vehicle- and nimesulide-treated ewes during the treatment period. All fetuses were alive at delivery or scheduled death.

CONCLUSIONS

These results indicate that the combination of an inhibitor of prostaglandin endoperoxidase H synthase type 2 with an oxytocin receptor antagonist is more effective in inhibition of preterm labor than is treatment with a prostaglandin endoperoxidase H synthase type 2 inhibitor alone. The clinical use of atosiban to prevent the oxytocin-stimulated increase in uterine activity associated with labor in combination with nimesulide may permit reduction of the dose of nimesulide used to a level that has minimal impact on fetal well-being.

Effects of hyperthermia on uterine blood flow and shunting through uterine arteriovenous anastomoses in the late-pregnant ewe

The effect of maternal hyperthermia on uterine blood flow (UBF) through the two main uterine arteries and on the proportion of UBF shunted through uterine arteriovenous anastomoses (AVAs) was investigated. Eight late-pregnant ewes were exposed to normothermic (22-23 degrees C) or hyperthermic (approximately 39 degrees C) ambient conditions for 8 h. UBF was measured in the left and right uterine arteries using flow probes and microspheres were injected into the uterine artery before, during and after the experimental period. The distribution of microspheres between the uterus and lungs was determined to calculate changes in capillary and AVA blood flows. Hyperthermia produced a significant (P<0.05) increase in maternal core temperature (+1.5 degrees C), increase in maternal blood pH (+0.21; P<0.05) and decrease in maternal pCO2 (-16.2 mmHg; P<0.05). Blood flow to the uterine horn ipsilateral to the corpus luteum (CL) remained unchanged during hyperthermia, whereas total UBF and blood flow to the contralateral uterine horn were significantly decreased (P<0.05), by 23.1% and 20.8%, respectively, of pre-heat control values. The proportion of UBF shunted through uterine AVAs during hyperthermia was not significantly different from values observed in normothermic ewes (21.9 +/- 0.7%). Mild to moderate hyperthermia in late-pregnant sheep induces respiratory alkalosis and decreases total blood flow to the uterus, brought about by a decrease in blood flow to the uterine horn contralateral, but not ipsilateral to the CL. Heat treatment does not alter the proportion of UBF traversing uterine AVAs.

Follicular development in transplanted fetal and neonatal mouse ovaries is influenced by the gonadal status of the adult recipient

OBJECTIVE(S)

To investigate the pattern of follicular development in transplanted fetal and neonatal mouse ovaries in the presence or absence of the recipient's own ovaries.

DESIGN

Controlled experiment.

SETTING

Academic research laboratory, Department of Physiology, Monash University, Clayton, Australia.

INTERVENTION(S)

Mouse ovaries from 16-day-old fetuses, 3-day-old neonates, and 10-day-old neonates were transplanted under the kidney capsule of adult female mice, which either retained their own ovaries in situ or were bilaterally ovariectomized.

MAIN OUTCOME MEASURE(S)

Histologic analysis.

RESULT(S)

By 4 weeks after transplantation, fetal and neonatal ovaries transplanted to ovariectomized recipients displayed a pattern of follicular development similar to that observed in in situ adult mouse ovaries. In contrast, follicular development did not progress beyond the early antral stage in fetal and 3-day-old ovaries transplanted to recipients that retained their in situ ovaries. However, 10-day-old ovaries transplanted to recipients that retained their in situ ovaries displayed full follicular development and corpora lutea formation by 8 weeks after transplantation.

CONCLUSION(S)

Follicular development in transplanted immature ovarian tissue is influenced by the age of the donor ovary and gonadal status of the recipient. (Fertil Steril(R) 2000;74:000-00. Copyright2000 by American Society for Reproductive Medicine.)

Gonadotrophin administration can benefit ovarian tissue grafted to the body wall: implications for human ovarian grafting

Ovarian grafting provides a strategy for clinical infertility treatment and is starting to be used in conjunction with ovarian tissue storage for patients at risk of early ovarian failure. As patients are starting to return for their frozen stored tissue we need to ascertain how to maximise follicle survival when this tissue is grafted back to the patient. For research purposes ovarian tissue is commonly grafted to the kidney capsule as the rich capillary bed at this site favours rapid graft revascularization. This is however not an ideal site for natural conceptions or for the harvest of mature oocytes for in vitro fertilization. While oocytes would be relatively easy to recover from grafts on the abdominal wall or subcutaneous tissue graft revascularization at these sites is slower and evidence indicates that fewer follicles survive. As gonadotropins can upregulate angiogenic growth factors in the ovary this study was designed to test whether the administration of exogenous gonadotropins would increase the number of surviving follicles in grafts placed at less vascularised sites. We showed that exogenous gonadotrophins, given to either the donor or the recipient, could increase the number of developing follicles but the magnitude of this effect was influenced by the timing of the injections relative to the time of grafting.

Evaluation of the long-term function of cryopreserved ovarian grafts in the mouse, implications for human applications

Ovarian tissue storage has several potentially very valuable clinical applications, including the management of young female patients that are at risk of premature menopause. Ovarian tissue collection, used alone or in combination with oocyte and embryo cryopreservation, may help these patients safeguard their own future fertility. All available evidence from animal studies indicates that grafting of frozen ovarian tissue should be feasible in the human. This study on the mouse shows that frozen thawed ovarian tissue grafts can restore long term fertility to previously ovariectomised recipients. This, and other available evidence, indicates that ovarian tissue collection and storage, used alone or in combination with oocyte or embryo collection, may help safeguard the fertility of patients at risk of premature menopause.

Uterine milk protein, a novel activin-binding protein, is present in ovine allantoic fluid

Activins are pluripotent growth factors that have recently been shown to be present in placental and fetal membrane preparations. Our previous studies have identified and purified activin A from ovine amniotic and allantoic fluids. In this study, ligand blots of side fractions from the isolation of activin A from allantoic fluid suggested the presence of activin-binding proteins other than follistatin. Further purification of one of these fractions involved two sequential reverse phase HPLC steps and a Superose 12HR fractionation. SDS-PAGE revealed a single protein band of 55 kDa, which was identified by NH2-terminal sequencing as ovine uterine milk protein (UTMP), a member of the serine protease inhibitor (serpin) superfamily of proteins. Further binding studies, using ligand blot techniques and Superose 12HR fractionation in the presence of [125I]activin, demonstrated UTMP to be an activin-binding protein with a lower affinity for activin than that of follistatin. A study of the specific binding behavior of UTMP to activin, using surface plasmon resonance, revealed an apparent equilibrium dissociation constant (Kd) of 49 +/- 25 nM, compared with the follistatin-activin Kd of 379 +/- 51 pM. Similar to another activin-binding protein, alpha2-macroglobulin, UTMP was unable to neutralize the bioactivity of activin in a bioassay based on the capacity of activin to inhibit the proliferation of an MPC-11 plasmacytoma cell line. The high concentrations of this protein in uterine fluid during pregnancy and its ability to bind activin suggest that UTMP may act as a low affinity, high capacity binding protein to sequester activin in the local uterine environment.

Effect of nitric oxide synthase inhibition on the uterine vasculature of the late-pregnant ewe

OBJECTIVES

We studied the role of nitric oxide in the maintenance of uterine vascular tone during pregnancy.

STUDY DESIGN

Late-pregnant ewes were instrumented with ultrasonographic flow probes on the left and right main uterine arteries. A catheter was passed retrogradely into 1 uterine artery from a tributary. In 14 animals nitric oxide synthase inhibitor (N omega-nitro-L-arginine methyl ester; L-NAME) was infused at 2 or 20 mg/kg during a 1-minute period into either the main left or right uterine artery.

RESULTS

The nitric oxide synthase inhibitor (20 mg/kg), infused into 1 uterine artery, significantly decreased uterine blood flow (P <.001) bilaterally, increased (P <.05) mean arterial pressure, and decreased heart rate (P <.05). The compound (when infused at 2 mg/kg) also significantly (P <.05) decreased uterine blood flow in the artery ipsilateral to, but not contralateral to, the infusion, with no change in mean arterial pressure and a decrease (P <.05) in heart rate.

CONCLUSION

During ovine pregnancy, endogenous nitric oxide production contributes to uterine vasodilatation.

Effect of labor induction on the expression of oxytocin receptor, cytochrome P450 aromatase, and estradiol receptor in the reproductive tract of the late-pregnant ewe

In this study, we investigated the timing of changes in aromatase, estradiol receptor, and oxytocin receptor expression in ovine uterine and placental tissues before parturition. Labor was induced by betamethasone injection into the fetus on Days 130-132 of pregnancy. Tissue samples were collected at injection and then every 14 h until labor (56 h) from four ewes at each time point. Samples were analyzed for aromatase, estradiol receptor, and oxytocin receptor expression by in situ hybridization; for oxytocin binding to its receptor using a specific antagonist; and for estradiol receptor quantitation by immunocytochemistry. Aromatase mRNA expression increased by 14 h postinjection (p < 0.02) in the fetal villi and remained high until labor. Expression of estradiol and oxytocin receptor mRNAs was unchanged in myometrium but increased in the endometrial luminal epithelium by 28 h (p < 0.05) and remained high until labor. Estradiol receptor protein concentration increased modestly at labor while oxytocin receptor binding in the luminal epithelium changed in parallel to the mRNA concentration.

IN CONCLUSION

1) induction of aromatase may facilitate the expression of endometrial estradiol and oxytocin receptors in the placentome, 2) changes in endometrial rather than myometrial oxytocin receptor may be important in inducing parturition, and 3) the transcription of estradiol receptor and oxytocin receptor in the uterine epithelium are positively correlated during parturition.

Co-localization of Rab3B and oxytocin to electron dense granules of the sheep corpus luteum during the estrous cycle

Oxytocin and its carrier protein, neurophysin, are both associated with luteal secretory granules which migrate from the paranuclear region to the cell membrane where exocytosis takes place. Rab3 proteins are thought to be associated with membrane vesicles or granules undergoing exocytotic fusion with the plasma membrane. The objective of this study was to determine whether Rab3B is co-localized with oxytocin within the same secretory granules of large luteal cells obtained from corpora lutea of 16 Merino cross ewes at day 3, 7, 12 or 15 of the estrous cycle using immunocytochemistry. The mean granule density (granules/microm3) was not significantly different (P > 0.05) between the days examined. Electron microscopic immunocytochemistry showed that oxytocin and Rab3B were co-localized to the secretory granules on all days evaluated. Rab3B immunostaining was primarily located within secretory granules scattered throughout the cytoplasm. The mean intensity of labelling (number of gold particles) for oxytocin per microm2 cytoplasmic luteal tissue was significantly decreased on day 15 compared to those observed on days 3, 7 and 12 of estrous cycle. No significant changes were observed in the mean intensity of the Rab3B label at the different times of the cycle. The present study provides evidence that a member of the subfamily of Rab proteins, Rab3B, is present and co-localized with oxytocin in the same secretory granules of the ovine corpus luteum. These results implicate Rab3B protein directly or indirectly in the hormone secretory pathway of ovarian tissue.

Ovine allantoic fluid contains high concentrations of activin A: partial dissociation of immunoactivity and bioactivity

In a preliminary study, allantoic fluid collected from pregnant sheep across gestational ages of 20-124 days contained significantly higher levels of activin bioactivity (189 +/- 74 ng/ml, mean +/- SE) than did amniotic fluid (3.2 +/- 0.6 ng/ml). Using a combination of chromatography steps, we isolated from 5 L of allantoic fluid approximately 612 microg of immunoactive activin, which eluted over 10 fractions from a C8 reversed-phase column. When these fractions were assayed in a rat pituitary cell culture bioassay, in a specific RIA, and in an activin A two-site ELISA, the RIA activity was skewed to the less hydrophobic side of the activin profile, while the bioactivity was skewed to the more hydrophobic forms. The activity measured in the two-site ELISA more closely matched the mass of activin as determined by laser densitometry. Amino-terminal sequencing of fractions containing either peak immunoactivity or bioactivity showed each to be identical to activin A. This was confirmed by internal sequences from a fraction that eluted in the area of overlapping immunoactivity and bioactivity. A peptide containing at least 18 amino acids at its amino terminus, which were identical to the conserved region of the acute-phase protein serum amyloid A, was identified in the most immunoactive activin fractions.

Effect of oestradiol on ovarian oxytocin secretion rate and luteolysis in the ewe after ovarian auto-transplantation

The release of ovarian oxytocin and uterine prostaglandin (PG)F2alpha in response to an oestradiol stimulus was investigated. On Day 15 post-oestrus, ten ewes with ovarian auto-transplants (n=5 per group) received an intra-muscular injection of either oestradiol benzoate (50 microg) or vehicle. Blood samples were collected from the ovarian and jugular veins at 30 and 0 min before, and at 15-min intervals up to 540 min after, injection. The secretion rate of ovarian progesterone remained elevated in four of five treated ewes and in all control ewes, indicating the presence of a functional corpus luteum. Peripheral oestradiol concentrations were significantly (P < 0.001) higher in treated than in control ewes. The number of ewes that released pulses of ovarian oxytocin > or =240 min following oestradiol benzoate injection was significantly (P < 0 05) greater than that in control ewes. Mean amplitude and area under both ovarian-vein oxytocin and jugular-vein 15 keto-13,14 dihydro prostaglandin F2alpha (PGFM) pulses were significantly increased in the treated ewes. These findings demonstrate that the administration of exogenous oestrogen provides a positive stimulus for the release of ovarian oxytocin and uterine PGF2alpha in the ovarian auto-transplanted ewe.

Oestrogenic effects of ICI 182,780, a putative anti-oestrogen, on the secretion of oxytocin and prostaglandin F2 alpha during oestrous cycle in the intact ewe

The effect of ICI 182,780, oestrogen antagonist, on the concentration of oxytocin and uterine PGF2 alpha was investigated in intact Border Leicester Merino cross ewes during the late oestrous cycle. Twelve cyclic ewes (n = 6 per group) were randomly assigned to receive, at 6 h intervals, intra-muscular injection of either peanut oil or ICI 182,780 (1.5 mg kg-1 day-1) in oil for 2 days, starting at 1900 h on day 13 until 1300 h on day 15 post-oestrus. Hourly blood samples were collected via a jugular catheter from 0800 h on day 14 for 37 h and then daily over days 16, 17 and 18 post-oestrus. Peripheral plasma concentrations of oxytocin, the metabolite of prostaglandin F2 alpha, 15-keto-13,14-dihydro-prostaglandin F2 alpha, (PGFM) and progesterone were measured by radioimmunoassay. All ewes treated with ICI 182,780 exhibited functional luteal regression as indicated by a marked reduction in plasma progesterone concentrations to less than 1000 pg/ml over the period of 18-36 h during sampling period on days 14 and 15 of the oestrous cycle. In five of six vehicle-treated ewes, progesterone concentrations declined between day 16 and day 18 post-oestrus. In the remaining control ewe, progesterone concentrations reach less than 1000 pg/ml within 36 h of the commencement of the sampling period. During the frequent sampling period, the number of oxytocin pulses in the ICI 182,780 treated ewes was significantly higher compared to control ewes (2.7 +/- 0.3 vs. 0.8 +/- 0.3). The mean amplitude of oxytocin pulses observed was also greater (70.4 +/- 19.5 pg/ml) in ewes treated with ICI 182,780, but was not significantly different from the control ewes (33.5 +/- 12.9 pg/ml). Oxytocin pulses may however have occurred following the initial two ICI 182,780 injections but before commencing blood sampling. The oxytocin pulses were detected at a mean of 3.2 +/- 0.2 h following each injection with ICI 182,780 during blood sampling. In the ICI 182,780-treated ewes, the pulsatile pattern of plasma PGFM in jugular blood samples over the 37 h sampling period on days 14 and 15 post-oestrus had a higher amplitude (512.9 +/- 158.9 vs 121.7 +/- 78.7 pg/ml) and pulse area (618.1 +/- 183.3 vs 151.5 +/- 102.9 (ph/ml)tau) compared to the vehicle-treated ewes (P < 0.05) respectively.. The average number of PGFM pulses observed per ewe was 3.0 +/- 0.7 in the ICI 182,780-treated group and was significantly (P < 0.02) higher than the number of pulses (0.5 +/- 0.3) observed in ewes treated with vehicle alone. The PGFM pulses were detected at 4.2 +/- 0.6 h following each injection with ICI 182,780 during blood sampling. The percentage of PGFM pulses that occurred coincidently with significant elevation of oxytocin concentrations was 44.4% in ICI 182,780-treated compared to 66.6% in control ewes. We conclude that administration of oestrogen antagonist ICI 182,780 accelerated development of the luteolytic mechanism by enhancing pulsatile secretion of oxytocin and PGFM which suggests that ICI 182,780 acts as an agonist for oxytocin and prostaglandin f2 alpha release in intact ewes when administered at 1.5 mg/kg/day over day 13 to 15 post-oestrus.

Stimulation of ovarian oxytocin secretion and uterine prostaglandin release by exogenous progesterone early in the cycle of the ovarian auto-transplanted ewe

The present study was undertaken to determine whether the administration of progesterone, early in the oestrous cycle, had an influence on ovarian oxytocin secretion and on peripheral concentrations of the prostaglandin F2 alpha metabolite 13,14-dihydro-15-keto PGF2 alpha (PGFM) in the ovarian auto-transplanted ewe. Twelve ewes with ovarian auto-transplants (n = 6 per group) were randomly assigned to receive an i.m. injection of progesterone (12.5 mg) or vehicle, twice a day, on days 1, 2 and 3 of the oestrous cycle. Beginning on day 7, blood samples were collected at intervals of 1 h from the ovarian and contralateral jugular veins for up to 70 h. Ovarian oxytocin secretion rate and jugular concentrations of PGFM and progesterone were determined by radioimmunoassay. The number of ewes that showed pulses of both ovarian oxytocin and PGFM was significantly (P < 0.05) greater in progesterone-treated ewes than in control ewes. In progesterone-treated ewes, the average number of ovarian oxytocin pulses per ewe was 9.66 +/- 5.5 (mean +/- SD) and the interval between pulses was 7.18 +/- 5.8 h. The mean amplitude and amount of oxytocin released, as calculated by the area under the curve of ovarian oxytocin pulses, were 6.27 +/- 1.98 ng min-1 and (10.05 +/- 8.91 ng min-1)tau, respectively (where tau is the number of hours between the last time point before and the first time point after a significant increase in hormone concentration was detected by the Pulsar program). The mean amplitude and area under the curve of PGFM pulses were 317.22 +/- 5.65 pg ml-1 and (383.36 +/- 1.77 pg ml-1)tau, respectively. The average number of pulses of plasma PGFM observed per ewe was 5.8 +/- 1.9 and interpulse interval for plasma PGFM pulses was 10.32 +/- 8.7 h between day 7 and day 9 after oestrus. These data indicate that administration of progesterone during the first 3 days of the oestrous cycle results in the premature release of ovarian oxytocin and uterine prostaglandin F2 alpha.

Physiological evidence for arteriovenous anastomoses in the uterine circulation of late-pregnant ewes

1. The objective of the present study was to determine whether arteriovenous anastomoses (AVA) are present in the uterine circulation of conscious, late-pregnant ewes. 2. Twenty late-pregnant ewes were assigned to two groups. In group 1, 15 microm coloured microspheres were injected into the uterine artery of the pregnant horn and the relative proportion of microspheres trapped in the uterus and lungs was determined. The percentage shunting of blood measured by this method was 17+/-3%, representing a blood flow of 164+/-39 mL/min (n = 12). Any contribution of ovarian, cervical, rectal and other vascular beds was specifically excluded in this group. 3. In group 2, total uterine capillary flow was measured using the reference blood flow method, by injecting 15 microm microspheres into the heart. Calibrated flow probes, placed on both main uterine arteries, concurrently measured total uterine blood flow. Total blood flow to the uterus (flow probe) was significantly greater (t = 3.415; P = 0.027) than uterine capillary flow (microspheres), indicating AVA shunting in the uterine circulation. Mean total blood flow to the uterus was 1749+/-160 mL/min, of which an average 25+/-5% (n = 5 sheep) was shunted. 4. The percentage AVA shunting for groups 1 and 2 was not significantly different (t = 1.219; P = 0.24) and, when combined, the mean percentage of uterine blood flow passing through AVA in the late-pregnant sheep was determined to be 19+/-3%. 5. The present study shows that AVA are present and patent in the uterine circulation of late-pregnant ewes and that they account for the shunting of approximately 20% of the uterine blood flow into the maternal venous circulation.

Changes in uterine endometrial phospholipids and fatty acids throughout the oestrous cycle and early pregnancy in the ewe

This study examined changes in ovine endometrial phospholipids and fatty acid concentrations associated with luteolysis and the establishment of pregnancy in the ewe on days 3, 12 and 15, respectively. Results from this study indicate that endometrial lipids increased as the oestrous cycle progressed from days 3 to 12 and 15, whereas during early pregnancy, endometrial lipids decreased on day 15 of pregnancy when compared to days 3 and 12 of pregnancy. Phosphatidylcholine followed a similar pattern to that of total lipids, with an increase in phosphatidylcholine concentrations as the oestrous cycle progressed. During the early stages of pregnancy, phosphatidylcholine increased from day 3 to day 12, but then returned to previous levels by day 15 of pregnancy. Phosphatidylethanolamine increased late in the oestrous cycle, on day 15 as compared to days 3 and 12. This increase did not occur during early pregnancy, with phosphatidylethanolamine concentrations being constant from day 3 to day 15 of pregnancy. Both phosphatidylinositol and phosphatidylserine followed a similar pattern to phosphatidylethanolamine during the oestrous cycle and remained constant during early pregnancy. The fatty acid content of the major phospholipids involved in prostaglandin synthesis were examined over the range of fatty acids from C14:0 to C24:1omega9. Although changes in arachidonic acid were observed, there were no clear indications that these changes were directly related to the changes in PGF2alpha synthesis.

Source of inhibin in ovine fetal plasma and amniotic fluid during late gestation: half-life of fetal inhibin

Immunoactive inhibin (ir-inhibin) concentrations were determined in chronically catheterized sheep between 120 and 145 days gestation. Maternal plasma ir-inhibin concentrations remained basal (0.19 +/- 0.05 ng/ml) throughout the period of study. Immunoactive inhibin concentrations in male and female fetal plasma were elevated above those observed in maternal plasma, with the concentrations in plasma of male fetuses (7.38 +/- 0.04 ng/ml) being significantly greater (p < 0.001) than those in female fetuses (1.07 +/- 0.14 ng/ml). The concentrations of ir-inhibin in amniotic fluid of ewes bearing male fetuses (10.93 +/- 1.55 ng/ml) were significantly greater than in ewes bearing female fetuses (2.81 +/- 0.32 ng/ml; p < 0.05) but not significantly different from the concentrations in male fetal plasma. Immunoactive inhibin concentrations decreased following surgery in gonadectomized fetuses, to 3.25 +/- 0.99 ng/ml within 6 h, and remained at a mean value of 0.75 +/- 0.38 ng/ml from 24 h after gonadectomy. The half-life of circulating inhibin in fetal plasma, estimated from the decay curve during the first 6 h after surgery, was 3.94 +/- 0.88 h. There was a significant (p < 0.05) decrease in the concentration of ir-inhibin in amniotic fluid after gonadectomy; however, this decrease occurred gradually over 7 days, and ir-inhibin concentrations did not fall to those concentrations observed in fetal circulation at any time after gonadectomy. It is concluded that the major source of circulating ir-inhibin in male fetal plasma, but not in amniotic fluid, is the gonads.

Transplantation of cryopreserved fetal ovarian tissue to adult recipients in mice

Sixteen-day-old fetal mouse ovaries were slowly frozen in 1.5 mol dimethylsulfoxide ml-1 and subjected to one of two thawing procedures--fast thaw or slow thaw. Fresh and frozen-thawed fetal ovaries were transplanted orthotopically (to the bursal cavity) to either bilaterally or unilaterally ovariectomized adult female recipients. Fresh fetal ovaries were also transplanted heterotopically (under the kidney capsule) to intact, bilaterally or unilaterally ovariectomized adult females. Transplantation of fetal ovaries to bilaterally ovariectomized adult recipients resulted in restoration of cyclic activity within 20.5 +/- 4.7 (mean +/- SEM) days or 23.4 +/- 0.8 days in orthotopic and heterotopic groups, respectively. Developing follicles and corpora lutea were observed within 4 weeks after transplantation of fetal ovaries to heterotopic sites and within 6 weeks after transplantation to orthotopic sites. After orthotopic transplantation, 33% of the recipients became pregnant. Orthotopic or heterotopic transplantation to intact of unilaterally ovariectomized recipients resulted in quiescence of the fetal ovary. After cryopreservation, transplantation of fetal ovaries to bilaterally ovariectomized recipients resulted in restoration of cyclic activity within 19.3 +/- 2.1 days and 23.4 +/- 5.1 days after transplantation in slow thaw and fast thaw groups, respectively. Fertility was restored to 86% of fast thawed and 25% of slow thawed fetal ovary transplants to bilaterally ovariectomized adult recipients. No ovarian tissue was observed on the side of the fetal graft in unilaterally ovariectomized recipients that received frozen-thawed fetal ovaries. These results demonstrate that cryopreserved fetal ovarian tissue can be transplanted to adult recipients with subsequent restoration of fertility and that this process is dependent on the absence of the ovaries of the recipients.

Oxytocin receptor development in ovine uterus and cervix throughout pregnancy and at parturition as determined by in situ hybridization analysis

The development of uterine oxytocin receptors is an important regulatory step in the initiation of labour. Paracrine production of oxytocin by uterine and placental tissues may also be involved in some species. Placentome, intercotyledonary endometrium, myometrium and fetal membranes were collected from 3-5 ewes each, at regular intervals throughout pregnancy and from eight ewes during labour. Localization of mRNA encoding oxytocin and its receptor was by in situ hybridization; oxytocin peptide concentrations were measured by radioimmunoassay and oxytocin receptor concentrations were measured by autoradiography and radioreceptor assay. In the intercotyledonary endometrium, mRNA encoding the oxytocin receptor was located in the luminal epithelium only. Both the epithelial and myometrial receptors were detected at low concentrations from the fourth week of gestation onwards, with a major increase associated with the onset of labour. In the placentomes, oxytocin receptors were localized to a stromal capsule surrounding the placental villi. Expression in this region was maximal in mid-gestation, declining in the second half of pregnancy and remaining low during labour. Cervical oxytocin receptors were detected at low concentrations in the epithelium and the muscular/connective tissue layers from day 22 of pregnancy onwards. There was no evidence for the local uterine production of oxytocin in the ewe; mRNA encoding oxytocin was undetectable and oxytocin concentrations were always < 23 pg g-1 wet mass of tissue. These results suggest that regulation of the timing of oxytocin receptor development varies between the different tissue types, despite a similar steroidal background. The receptors in the luminal epithelium are probably associated with the ability of exogenous oxytocin to induce the release of PGF2 alpha throughout most of pregnancy. The increase in receptors in both the intercotyledonary endometrium and myometrium at term suggest an involvement in labour, whereas their role in caruncular stroma in mid-pregnancy is unknown.

Oxytocin-induced prostaglandin F2 alpha release and endometrial oxytocin receptor concentrations throughout pregnancy in ewes

Endometrial oxytocin receptor concentrations and oxytocin-induced plasma concentrations of 13,14,dihydro-15-keto prostaglandin F2 alpha were investigated on days 14 and 17 of the oestrous cycle and on days 14, 17, 25, 65, 85 and 145 of gestation in ewes. Total 13,14,dihydro-15-keto prostaglandin F2 alpha release in response to a bolus injection of oxytocin was significantly (P < 0.05) higher at luteolysis (day 17 of the oestrous cycle) than at any other stage of the oestrous cycle or in early gestation. On days 65, 85 and 145 of gestation, total prostaglandin release was significantly (P < 0.05) increased compared with earlier in gestation. Maximum concentrations of 13,14,dihydro-15-keto prostaglandin F2 alpha in response to oxytocin followed a similar pattern. Oxytocin receptor concentrations reflected total oxytocin-induced 13,14,dihydro-15-keto prostaglandin F2 alpha release, with increased oxytocin receptor concentrations occurring on day 17 of the oestrous cycle, compared with those observed on day 14 of the oestrous cycle and on days 14, 17 and 25 of gestation. By day 65 of gestation, oxytocin receptor concentrations were again increased. However, on days 85 and 145 of gestation, oxytocin receptor concentrations had decreased to concentrations similar to those observed in early gestation. These results indicate that oxytocin-induced 13,14,dihydro-15-keto prostaglandin F2 alpha release during early gestation is minimal despite the presence of endometrial oxytocin receptors. In mid-gestation, oxytocin-stimulated 13,14,dihydro-15-keto prostaglandin F2 alpha release is increased with a concomitant increase in uterine oxytocin receptor concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Implication of inhibin and related proteins in fetal development

Initial studies on inhibin, activin and follistatin focussed on their role as regulators of adult gonadal function via feedback regulation of anterior pituitary hormones and via intragonadal control of steroid hormones. The discovery of isoforms of follistatin which are either secreted or retained on the cell surface and which bind activin and, to a lesser extent, inhibin adds a further dimension to the regulation of these peptides. More recently, the cloning of inhibin and activin, and the observation of their close homology to the transforming growth factor-beta family of peptides, has led to an interest in their possible role as growth and differentiation factors. Activin, inhibin and follistatin are expressed in embryonic and fetal tissues, as well as in the placenta. However, although activin is a potent regulator of growth and differentiation in a number of cell types, their role in embryonic and fetal development has yet to be established. High concentrations of inhibin have been observed in the fetal gonads, particularly the testes, and in the fetal adrenals of a number of species and a sex difference in fetal plasma concentrations has also been observed. Although the stimulus for high concentrations of inhibin in the fetus is not know, they are associated with decreased testicular testosterone and a decrease in the concentration of circulating follicle-stimulating hormone (FSH); this suggests that, as in the adult, inhibin may be involved in the regulation of fetal testicular androgen and pituitary FSH secretion during late gestation. The recent reports of elevated concentrations of inhibin and, particularly, activin in amniotic fluid during late gestation and its ability to stimulate the production of prostaglandin E2 by fetal membranes provides yet another potential role for this hormone in the regulation of events leading to parturition.

Effects of luteolytic doses of prostaglandin F2 alpha and cloprostenol on concentrations of progesterone, luteinizing hormone, follicle-stimulating hormone, glucose, insulin, growth hormone, thyroxine, prolactin and cortisol in jugular plasma of lactating dairy cows

Three groups of five lactating dairy cows in the mid-luteal phases of oestrous cycles were given an injection (at time 0 h) of the naturally-occurring prostaglandin F2 alpha (PGF2 alpha) or cloprostenol (a synthetic analogue of PGE2 alpha) at doses recommended for inducing luteolysis, or injection vehicle. Concentrations of glucose and hormones in jugular plasma were measured from 26 h before to 12 h after the injections and the significance (P < 0.05) of the effects of the prostaglandins on these concentrations was determined. Both prostaglandins induced falls in progesterone concentration and rises in luteinizing hormone concentration; neither influenced follicle-stimulating hormone. PGF2 alpha increased glucose concentration; neither prostaglandin influenced insulin concentration. Both prostaglandins increased growth hormone concentration and resulted in declining thyroxine concentration. PGF2 alpha increased prolactin and cortisol concentration. There were, however, no significant differences between the effects of the two prostaglandins on any hormone (or glucose) concentration.

Inhibin and follistatin concentrations in fetal tissues and fluids during gestation in sheep: evidence for activin in amniotic fluid

The concentrations of inhibin and follistatin in amniotic fluid and in tissue extracts from the placenta, gonads and adrenals of fetal sheep were measured using radioimmunoassays. These tissue extracts were from whole fetuses from days 16 to 45 and from the individual organs from day 46 to 145 (term) and were assayed at multiple dilutions. The capacity of these extracts to alter FSH production of rat anterior pituitary cells in culture was also assessed at multiple dilutions. Immunoactive inhibin concentrations in amniotic fluid from both sexes increased during gestation and levels were significantly greater in males than females. Peak concentrations of immunoreactive inhibin of 11.2 +/- 1.9 ng/ml were found in males at 116-125 days of gestation. Follistatin concentrations did not change throughout gestation and no significant difference was noted between sexes. Mean follistatin levels throughout gestation were 3.0 +/- 0.9 ng/ml for males and 3.7 +/- 0.9 ng/ml for females. Despite the potential for FSH inhibition by inhibin and follistatin, amniotic fluid from both sexes at all stages of gestation stimulated FSH secretion in the pituitary cell bioassays, suggesting the presence of activin which was confirmed by the measurement of immunoactive activin (13.3 +/- 2.5 ng/ml) in a specific radioimmunoassay. Maximum concentrations of immunoactive and bioactive inhibin in placental extracts were observed in late gestation (2.2 +/- 0.6 and 3.8 +/- 1.6 ng/g respectively) and there was no significant difference between sexes. Follistatin concentrations in placental cotyledons ranged from 11.5 to 27.1 ng/g with no significant difference between sexes. In view of the higher follistatin concentrations compared with inhibin, it is likely that the capacity of placental extracts to suppress FSH production by pituitary cells in culture is due predominantly to follistatin. Immunoactive inhibin was observed in high concentrations in the fetal testis throughout gestation; with concentrations increasing to a maximum of 1993.0 +/- 519.7 ng/g at 126-135 days of gestation with a ratio of bioactive: immunoactive inhibin of 1:20. Although bioactive and immunoactive inhibin was also observed in fetal ovaries and adrenals from both male and female fetuses, concentrations were lower than those observed in fetal testes. Follistatin concentrations in the fetal testis were elevated between 70 and 95 days (97.6 ng/g) and then declined. Similar concentrations were found in the adrenal glands of both sexes (males 83.5-103.3 ng/g: females 55.3-95.8 ng/g).(ABSTRACT TRUNCATED AT 400 WORDS)

The isolation of activin from ovine amniotic fluid

During a study of the levels of inhibin and follistatin in ovine amniotic fluid, we noted that although detectable levels of immunoactive inhibin and follistatin were found throughout gestation, the addition of amniotic fluid to a rat anterior pituitary cell culture resulted in a stimulation, rather than the expected suppression, of FSH concentrations. These data suggested the possibility that activin was present in amniotic fluid. We, therefore, set out to isolate the molecules responsible for this activin-like activity and determine their structure. Amniotic fluid, collected from pregnant sheep between 120-140 days gestation, was used as starting material in the purification and diluted in parallel to a human activin-A standard in the activin RIA employed to monitor the purification. A total pool of 7.4 liters amniotic fluid was processed by dye affinity chromatography, hydrophobic interactive chromatography, gel filtration, and a series of reverse phase HPLC steps. Polyacrylamide gel electrophoresis of fractions from the final HPLC step, which showed both activin immunoactivity and bioactivity, revealed a band with a mol wt of 25.3 kilodaltons (kDa), which reduced to 15.8 kDa, and a minor band of 45 kDa, which reduced to 25 kDa. NH2-terminal amino acid sequences of several active fractions from the same region were identical to the known sequence of ovine activin-A. The identification of immunoactive activin, follistatin, and inhibin in amniotic fluid raises the question of the sites of production of these proteins and their interactions and role in fetal physiology.

Oxytocin receptor blockade and prostaglandin release in late pregnant sheep

The oxytocin receptor inhibitor 1-deamino-2-D-Tyr-(oET)-4-Thr-8-orn-oxytocin (CAP) was infused into late pregnant sheep. Basal and oxytocin-induced prostaglandin (PG) concentrations in maternal and fetal plasma were determined. CAP had no significant effect on maternal PGFM or PGE2 or fetal PGF2 alpha, PGFM or PGE2 concentrations during late pregnancy or at term. PGF2 alpha was not detectable in maternal peripheral plasma. CAP infusion did not affect fetal well-being. Oxytocin injection to the mother caused a significant, dose-dependent, increase in maternal plasma PGFM concentrations but did not alter maternal PGE2 concentrations or fetal PGF2 alpha and PGE2 concentrations. The increase in maternal PGFM concentrations brought about by oxytocin injection was decreased during intrauterine infusion of CAP over the range of 12.5-100 micrograms/min. A rationale for the use of oxytocin receptor blockade for the prevention of premature labor is thus provided.

Effect of the antiprogestin RU486 on uterine sensitivity to oxytocin in ewes in late pregnancy

The effect of RU486, a synthetic progesterone receptor antagonist, on basal uterine prostaglandin (PG) release and release in response to oxytocin injection has been investigated in late-pregnant sheep (days 135-140 of gestation). Fifteen hours after i.m. injection of RU486 (50 mg; n = 5) or vehicle alone (n = 4), bolus injections of oxytocin (50, 500 and 5000 mU) were administered via a uterine artery ipsilateral to the pregnant uterine horn at 2-hourly intervals. Utero-ovarian vein concentrations of 13,14-dihydro-15-keto PGF2 alpha (PGFM) and PGE2 were determined before and during oxytocin stimulation. Basal concentrations of both PGFM and PGE2 were significantly (P < 0.001) increased in ewes 15 h after RU486 administration compared with ewes receiving vehicle alone. Concentrations of PGFM, but not PGE2, increased significantly (P < 0.001) following injection of each dose of oxytocin in both treated and untreated animals. The response to oxytocin, measured both as the area under the curve and as the peak height of PGFM release, was significantly (P < 0.05) greater in RU486-treated ewes. There was no significant effect of oxytocin on the area or peak height of PGE2 response in either RU486-treated or control animals. These results demonstrate that treatment of late-pregnant ewes with RU486 results in an increase in basal uterine PGFM and PGE2 as well as oxytocin-stimulated PGFM release.

Interaction between oxytocin and prostaglandin F2 alpha during luteal regression and early pregnancy in sheep

The pulsatile release of oxytocin from the corpus luteum in the sheep is responsible for the pulsatile release of prostaglandin F2 alpha (PGF2 alpha) from the uterus at luteolysis. It has been proposed that PGF2 alpha also reinforces this process by stimulating the release of oxytocin from the corpus luteum. It is, however, unlikely that PGF2 alpha is the major stimulus for oxytocin release at this time. Although the stimulus for the pulsatile release of oxytocin from the corpus luteum appears to reach the ovary from the peripheral circulation, the nature of the stimulus is unknown. Pulses of oxytocin originating from the corpus luteum have also been observed during early pregnancy, but the release of PGF2 alpha, in response to this signal, is abrogated in some way by ovine trophoblast protein-1 (oTP-1). This protein has been shown to inhibit endometrial prostaglandin production and to decrease the amount of PGF2 alpha released in response to oxytocin. Reduction of uterine oxytocin receptor concentrations by conceptus secretory proteins or by interferons related to oTP-1 remains equivocal. Inhibition of uterine oxytocin receptors is, however, probably the major mechanism that prevents luteal regression during early pregnancy. In cyclic sheep the specific inhibition of uterine oxytocin receptors by 1-deamino-2-D-Try (oET)-4-Thr-8-Orn-oxytocin (CAP), a synthetic oxytocin receptor antagonist, inhibits luteal regression and suppresses pulsatile, but not basal, secretion of uterine PGF2 alpha. Thus, the effects of CAP directly parallel the endocrinological changes that occur in early pregnancy in the sheep.

Regulation of expression of male-specific rat liver microsomal 3 beta-hydroxysteroid dehydrogenase

In the steroidogenic pathways present in the gonads and adrenal cortex, 3 beta-hydroxysteroid dehydrogenase isomerase (3 beta HSD) is a key enzyme which controls the formation of delta 4-3-ketosteroids from delta 5-3 beta-hydroxysteroids. Herein, we used an antibody against human placental 3 beta HSD and a rat testicular 3 beta HSD cDNA probe to study the expression of rat liver 3 beta HSD mRNA and protein. Rat liver microsomal 3 beta HSD activity has been previously reported to exhibit a significant sex difference, with much higher activity in the male. We have shown an age-dependent increase in levels of immunoreactive 3 beta HSD through the time of maturation of the male rat. The immunoreactive protein, of similar molecular size to the human placental and rat testicular 3 beta HSD, was localized to the microsomal fraction of liver and was concentrated in pericentral locations. Immunoreactive protein was not detected in liver of immature (before 25 days of age) rats of either sex or in adult female liver. Northern blot analysis of liver and testicular RNA with a rat testicular 3 beta HSD cDNA probe revealed the presence of a 1.6-kilobase mRNA species in addition to the major 2.1-kilobase mRNA species in adult male liver, neither of which was detected in immature or adult female liver RNA. Hypophysectomy of female rats or treatment with testosterone implants caused induction of liver 3 beta HSD protein, while continuous infusion of GH to male rats decreased the level of 3 beta HSD protein. Similarly, the levels of the mRNA species were decreased after GH treatment. Using [3 alpha-3H]dehydroepiandrosterone as substrate for 3 beta HSD activity, we determined the apparent Km for liver microsomal NAD(+)-dependent 3 beta HSD activity to be 20 microM in both adult male and female liver and was much greater than the Km of rat Leydig tumor 3 beta HSD activity (0.2 microM). Liver 3 beta HSD activity was inhibited by trilostane, a proven inhibitor of gonadal and adrenal 3 beta HSD activity. A rat liver 3 beta HSD cDNA was isolated from a male liver cDNA library that was closely related to the type II 3 beta HSD form of rat ovary but different from type III liver 3 beta HSD. The enzyme obtained upon expression of this cDNA had properties characteristic of male-specific NAD(+)-dependent liver microsomal 3 beta HSD (i.e. high apparent Km for dehydroepiandrosterone) and distinct from those of the high affinity gonadal type I 3 beta HSD.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of oxytocin and estradiol on uterine prostaglandin release in nonpregnant and early-pregnant ewes

The effects of exogenous oxytocin (OT) and estradiol-17 beta (E2) on plasma concentrations of prostaglandin (PG) E2 and 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) were investigated on Day 14-15 (NP) of the estrous cycle and Days 14-16 (PI) and 21-25 (EP) of pregnancy in the ewe. Basal concentrations of PGFM were significantly elevated in utero-ovarian venous (UOV) plasma on Day 14 of pregnancy (4.05 +/- 0.81 nM, mean +/- SEM) compared to that observed on Day 14 of the cycle or Days 21-25 of pregnancy (2.29 +/- 1.3 nM and 1.06 +/- 0.56 nM, respectively). PGFM release increased significantly following intera-arterial bolus injections of 50, 500, and 5000 mU OT at 2-h intervals in all experimental groups. There was no significant difference in area and peak height of the PGFM response between the 3 groups studied. The time to peak PGFM response was, however, significantly longer in the PI group. No significant changes in concentration of PGFM were observed in any experimental group following 1-h infusions of E2 at 5, 50, and 500 pmol/min. Long-term (15-18 h) infusion of E2 at 83 pmol/min increased the peak height of the OT-induced PGFM response at both stages of gestation studied. PGE2 concentrations in UOV plasma were less than 0.05 nM in all samples studied. These results demonstrate that PG release can be induced in response to OT during the period in which ovine trophoblastic protein-1 (oTP-1) is released by the conceptus. During pregnancy, oTP-1 does not appear to inhibit the E2 induction of uterine OT receptors.

Regulation of oxytocin secretion by the ovine corpus luteum: effect of activators of protein kinase C

The effect of protein kinase C activation and dibutyryl cyclic AMP on oxytocin secretion by ovine luteal tissue slices was investigated. Several putative regulators of luteal oxytocin secretion were also examined. Oxytocin was secreted by luteal tissue slices at a basal rate of 234.4 +/- 32.8 pmol/g per h (n = 24) during 60-min incubations. Activators of protein kinase C: phorbol 12, 13-dibutyrate (n = 8), phorbol 12-myristate, 13-acetate (n = 4) and 1,2-didecanoylglycerol (n = 5), caused a dose-dependent stimulation of oxytocin secretion in the presence of a calcium ionophore (A23187; 0.2 mumol/l). Phospholipase C (PLC; 50-250 units/l) also caused a dose-dependent stimulation of oxytocin secretion by luteal slices. Phospholipase C-stimulated oxytocin secretion was potentiated by the addition of an inhibitor of diacylglycerol kinase (R59 022; n = 4). These data suggest that the activation of protein kinase C has a role in the stimulation of luteal oxytocin secretion. The results are also consistent with the involvement of protein kinase C in PLC-stimulated oxytocin secretion. The cyclic AMP second messenger system does not appear to be involved in the control of oxytocin secretion by the corpus luteum.

The fate and uptake of murine epidermal growth factor in the sheep

125I-Labelled murine epidermal growth factor (EGF) was injected or infused into conscious ewes through the jugular vein. Its disappearance from the circulation and the pattern of its distribution in other body tissues and compartments were observed. Single bolus injections of 125I-labelled EGF resulted in a transient peak of radioactive EGF in the circulation which occurred within 1 min of the injection. This was followed by a very rapid fall in radioactivity in the plasma (t1/2 approximately 1 min) and the gradual appearance of 125I-labelled EGF in the urine. Immunoprecipitable 125I-labelled EGF could be detected in urine within 5 min of the start of the experiment. 125I-Labelled EGF accumulated in the urine for several hours following the injection, although with increasing time a substantial amount of non-immunoprecipitable iodide was also found. The rate of disappearance of the 125I-labelled EGF from the plasma of the ewe was found to be faster than the rate of disappearance of free [125I]iodide that had been injected into the ewe. 125I-Labelled EGF was also administered by a continuous infusion following an initial bolus injection. This again resulted in a rapid initial fall in radioactivity in blood, followed by a slow rise throughout the period of the infusion. When the infusion was stopped, there was a 15-min period of rapid readjustment, after which the radioactivity in the blood fell at a much slower rate (t1/2 approximately 70 min) than was seen initially. Again, intact 125I-labelled EGF was transferred to urine throughout the experiment. At autopsy, 125I-labelled EGF was increased in bile, liver, thyroid and kidney. Although most of the 125I found in the thyroid was free iodide, some EGF-like material was also present. There was also EGF-like material found in both the kidney cortex and the kidney medulla. These results indicate that complex multi-compartment pathways for the uptake, distribution and clearance of 125I-labelled EGF exist in the sheep.

Effect of gamma 3 or gamma 2 melanocyte stimulating hormone on steroidogenesis in the fetal sheep during late gestation

We have measured circulating concentrations of gamma 3 Melanocyte Stimulating Hormone (MSH) in fetal sheep between 111 and 145 days gestation. There was no significant effect of gestational age on the fetal plasma concentrations of gamma 3 MSH throughout this period. We have examined the role of gamma-MSH related peptides in the control of fetal adrenal steroidogenesis and found no significant change in fetal plasma cortisol or pregnenolone concentrations during a 60-72 h infusion of saline, gamma 2 MSH or gamma 3 MSH in sheep between 130 and 135 days gestation. Therefore although we have demonstrated the presence of gamma MSH related peptides in fetal sheep plasma during late gestation we have failed to demonstrate a role for gamma 3 or gamma 2 MSH in the changes in fetal steroid concentrations which occur prepartum.

Control of oxytocin secretion by ovine corpora lutea: effects of arachidonic acid, phospholipases, and prostaglandins

The involvement of arachidonic acid and arachidonic acid metabolites in the control of oxytocin secretion by ovine corpus luteum was investigated, using slices of luteal tissue incubated in vitro. Oxytocin was secreted at steady rates by luteal slices, during 60-min incubations (315.0 +/- 45.3 pg/mg.h). The secretion of oxytocin was stimulated by arachidonic acid, phospholipase A2 (PLA2), and phospholipase C (PLC) in a dose-dependent manner. The highest doses of arachidonic acid, PLA2, and PLC used stimulated oxytocin secretion by 145.8 +/- 23.0% (P less than 0.01; n = 6), 331.5 +/- 42.4% (P less than 0.02; n = 4), and 955.5 +/- 278.6% (P less than 0.01; n = 4), respectively. Oxytocin secretion by luteal slices was not affected by either prostaglandin F2 alpha (PGF2 alpha) or PGE2 over a concentration range from 3-3000 nM. Furthermore, inhibitors of the cyclo-oxygenase pathway of arachidonic acid metabolism did not consistently affect arachidonic acid and PLA2-stimulated oxytocin secretion. Nordihydroguaiaretic acid, which inhibits 5-lipoxygenase, however, totally abolished arachidonic acid- and reduced PLA2-stimulated oxytocin secretion. The presence of CoCl2 in the incubation medium also significantly reduced basal and PLA2- and PLC-stimulated oxytocin secretion [P less than 0.05 (n = 5), P less than 0.05 (n = 5), and P less than 0.01 (n = 6), respectively]. We have shown that oxytocin secretion from slices of ovine corpus luteum incubated in vitro is stimulated by exogenous and endogenously released arachidonic acid. The data show that PGF2 alpha and PGE2 do not have a role in luteal oxytocin secretion in vitro and PG formation does not appear to be involved in the stimulation of oxytocin secretion elicited by arachidonic acid or PLA2. Arachidonic acid may have its effect via the lipoxygenase pathway.

Passive immunization of pregnant goats against ovine LH

Groups of three goats at 50, 90 and 130 days of gestation were passively immunized against ovine LH (oLH) by i.v. infusion of 8 ml serum equivalent of the immunoglobulin fraction of rabbit anti-oLH serum (LHAS). Goats at the same stages of gestation as above served as controls and received 8 ml serum equivalent of the immunoglobulin fraction of normal rabbit serum (NRS). Plasma concentrations of progesterone were determined by specific radioimmunoassay of blood collected at 20-min intervals from 6 h before infusion of LHAS or NRS to 12 h after infusion. Less frequent sampling was performed from 2 days before to 6 days after infusion. Plasma from all LHAS-immunized goats exhibited binding of oLH. Twelve hours after immunization, titres ranged from 1:135 to 1:215. All LHAS-treated goats had titres of less than 1:10 by 5 days after immunization, but a low level of oLH binding was still detectable. Treatment with LHAS or NRS did not shorten the length of gestation, with all goats delivering live offspring between 142 and 147 days after conception. Plasma concentrations of LH ranged from less than 0.15 micrograms/l to 4.8 micrograms/l and were greater than 0.15 micrograms/l in 181 of 255 samples (71%) for both the NRS-treated group, throughout the experiment, and the LHAS-treated groups before infusion of antiserum. Luteinizing hormone was not detectable in plasma samples obtained after LHAS infusion in goats at 50 or 130 days of pregnancy. Plasma concentrations of LH exceeded 0.15 micrograms/l in only five of 51 (10%) samples in 90-day-pregnant goats treated with LHAS, the maximum value reached being 0.80 micrograms/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral plasma concentrations of pregnenolone sulphate, pregnenolone, progesterone and 20 alpha-hydroxy-4-pregnen-3-one in ewes throughout the oestrous cycle

Pregnenolone sulphate, pregnenolone, progesterone and 20 alpha-hydroxy-4-pregnen-3-one concentrations in peripheral plasma of normal cyclic ewes were measured by radioimmunoassay. The concentrations of these steroids were correlated with that of progesterone. The concentrations of all the steroids measured in peripheral plasma varied in a cyclic manner and showed a significant (P less than 0.05) positive correlation with the concentration of progesterone. Peripheral plasma concentrations of these steroids in ovariectomized and ovariectomized, dexamethasone-treated ewes were also determined. The plasma concentration of progesterone in ovariectomized ewes was undetectable but the concentrations of pregnenolone sulphate, pregnenolone and 20 alpha-hydroxy-4-pregnen-3-one remained similar to those observed at oestrus. Administration of dexamethasone to ovariectomized ewes had no effect on pregnenolone sulphate or pregnenolone concentrations but 20 alpha-hydroxy-4-pregnen-3-one concentrations, which were already very low, decreased further. It is proposed that the ovary, probably the corpus luteum, secretes pregnenolone sulphate, pregnenolone and 20 alpha-hydroxy-4-pregnen-3-one; however, pregnenolone sulphate and 20 alpha-hydroxy-4-pregnen-3-one may also arise from the metabolism of circulating pregnenolone and progesterone.

Secretion of oxytocin and progesterone by ovine corpora lutea in vitro

The mechanisms involved in the control of oxytocin and progesterone secretion by the ovine corpus luteum have been investigated in vitro using luteal slice incubations. Oxytocin and progesterone were secreted at constant rates from luteal slices for 2 h of incubation (366 +/- 60 pg X mg X h and 18.9 +/- 0.18 ng X mg X h, respectively). Secretion of progesterone, but not of oxytocin, was significantly (p less than 0.02) stimulated in the presence of ovine luteinizing hormone. Incubation of luteal slices in medium containing 100 mM potassium, however, resulted in increased secretion of oxytocin and, to a lesser extent, of progesterone (294 +/- 59% and 142 +/- 15%, respectively, p less than 0.05). Basal oxytocin secretion was reduced during incubation in calcium-free medium, compared to secretion in the presence of calcium (70 +/- 15 and 175 +/- 25 pg X mg X 20 min, respectively, p less than 0.01), whereas progesterone secretion was not altered in the absence of calcium. Secretion of both hormones by luteal slices was stimulated by the addition of the calcium ionophore A23187 (p less than 0.05). Addition of prostaglandin F2 alpha (2.8 microM) had no effect on secretion of either oxytocin or progesterone. We have demonstrated that oxytocin and progesterone can be stimulated, independently, from corpus luteum slices incubated in vitro. The pattern of release is consistent with the proposal that oxytocin, but not progesterone, is associated with and actively released from luteal secretory granules. Our results also indicated that prostaglandin F2 alpha does not directly stimulate release of oxytocin or progesterone from luteal cells in vitro.

The interaction of hCG, hydroxysteroids and interstitial fluid on rat Leydig cell steroidogenesis in vitro

Rat testicular interstitial fluid and hydroxycholesterol both stimulated testosterone production by isolated Leydig cells in vitro in a dose-dependent manner, but the dose-response lines were not parallel. The addition of cycloheximide blocked the stimulation by interstitial fluid but not that of hydroxycholesterol. Use of the compounds SU 10603 and cyanoketone (which inhibit 3 beta-hydroxysteroid dehydrogenase and 17 alpha-hydroxylase respectively) or aminoglutethimide (which acts on the cholesterol side-chain cleavage enzyme) showed that the stimulatory factor(s) in interstitial fluid stimulated steroidogenesis at the cholesterol side-chain cleavage enzyme, before the conversion of pregnenolone. This enzyme is rate-limiting in the synthesis of testosterone by Leydig cells and a site of action of LH; therefore, these results support the view that an interstitial fluid factor may be involved in the paracrine regulation of testicular steroidogenesis.

Comparison of particle-associated progesterone and oxytocin in the ovine corpus luteum

The subcellular distribution of progesterone and oxytocin within the ovine corpus luteum was investigated using differential and density gradient centrifugation. Progesterone and oxytocin were associated with particles which sedimented to a density of 1.049-1.054 g/ml and 1.054-1.061 g/ml respectively. Particle-associated progesterone did not, however, display physical or biochemical characteristics consistent with its storage within secretory granules. When particle-associated progesterone was incubated in HEPES buffer at 37 degrees C, 70% of the total progesterone was recovered in the incubation medium. The remaining stable particle-associated progesterone was not affected by treatments which stimulated oxytocin release and which have been shown to cause the release of peptides and biogenic amines from secretory granules. These results suggest that particle-associated progesterone represents the intercalation of progesterone into cell membranes and they do not support the hypothesis that progesterone is stored, in a protein-bound form, in luteal secretory granules.

Induction of premature delivery in sheep following infusion of cortisol to the fetus. I. The effect of maternal administration of progestagens

Premature induction of delivery in fetuses infused with graded doses of cortisol was brought about in 123.5 +/- 7.7 h (mean +/- SEM, n = 6) after the start of cortisol infusion. This treatment caused a rise in fetal plasma cortisol similar to that observed at normal delivery. Maternal and fetal progesterone and 20 alpha-dihydroprogesterone concentrations decreased to basal levels during infusion of cortisol to the fetus. Induction of premature delivery was delayed or prevented by concomitant treatment of the ewe with progestagen. Maternal intramuscular injection of 100 mg progesterone, 2 times daily, prevented delivery in four of four ewes treated during the time that cortisol was infused into the fetus (11-13 days). Maternal plasma progesterone and 20 alpha-dihydroprogesterone concentrations were maintained during this period, but fetal plasma progesterone concentrations decreased to the same extent as in the fetuses infused with cortisol alone. A single intramuscular injection of 250 mg of medroxyprogesterone acetate to ewes on the day before commencement of infusion of cortisol to the fetus prevented delivery in four of six ewes during the time that cortisol was infused for 9, 13, 14, and 15 days, respectively. One ewe delivered a live lamb at 133.5 h and another at 147.7 h after the start of infusion of cortisol to the fetus. Maternal and fetal plasma cortisol, progesterone, and 20 alpha-dihydroprogesterone concentrations were similar to those observed during infusion of cortisol alone to the fetus. Although fetal cortisol concentrations rose in a similar fashion, and to a similar extent, in all three groups during infusion of cortisol to the fetus, fetal 11-desoxycortisol concentrations only rose above basal levels close to the time of delivery in cortisol-infused fetuses or, in the progestagen-treated groups, when the fetus showed signs of being stressed.

Inhibition of progesterone secretion by a 3 beta-hydroxysteroid dehydrogenase inhibitor in late pregnant sheep

The role of progesterone in the initiation of parturition in the sheep is unclear. Whether a decrease in plasma progesterone is the essential prerequisite for the initiation of parturition or whether other factors also maintain uterine quiescence until delivery is not known. The effect of withdrawal of progesterone on the initiation of parturition has been investigated by intravenous administration of trilostane, a 3 beta-hydroxysteroid dehydrogenase delta 5-4 isomerase inhibitor, to late pregnant sheep. Twenty-five or 100 mg trilostane caused a precipitous decrease in plasma progesterone to about 30% of preinjection levels. Progesterone remained depressed for up to 7 days after treatment. 13,14-Dihydro-15-keto-prostaglandin F2 alpha (PGFM) became elevated between 7 and 36 h after trilostane injection but gradually returned to preinjection levels during the subsequent 36 h, at a time when plasma progesterone was still depressed. Four of 11 animals treated with 100 or 200 mg trilostane aborted prematurely at a time when plasma PGFM was maximal and plasma progesterone minimal. There were no consistent changes in plasma estradiol-17 beta or ovine placental lactogen concentrations after treatment with trilostane. It is suggested that a decrease in plasma progesterone will cause a transient increase in plasma PGFM concentrations which can lead to the premature initiation of parturition. In some instances the myometrium does not appear to respond to the elevated PGFM concentrations even when the estrogen:progesterone ratio is elevated by a decrease in plasma progesterone.

Relationship between electrical activity of the uterus and surgically isolated myometrium in the pregnant and nonpregnant ewe

Rhythmic contractions occur in the sheep uterus at oestrus and during pregnancy from about 65 days to term (145 days). To define factors responsible for these contractions we have examined and quantified the degree of synchronization of electrical activity in the uterus and isolated segments of myometrium in 3 types of experiments. In the first, a segment of myometrium was totally separated from the uterus. After a period of 9-16 days the isolated tissue developed a typical pattern of uterine activity which showed no significant degree of synchronization with EMG bursts in the body of the uterus. During labour, the isolated tissue showed changes in activity similar to those observed in the uterus. In the 2nd experiment, the tubal end of one of the uterine horns was severed from the uterus, but a connection was retained with the uterus via the oviduct and ovarian blood vessels. Activity in the partly isolated segment remained in synchrony with the uterus. In a 3rd experiment, impulse propagation through nerves and smooth muscle to the tip of a horn was disrupted by severing 'the tip' from the uterus while its blood supply from the ovarian vessels was retained. The blood vessels were momentarily frozen, and denervation confirmed by monoamine histofluorescence. In 5 out of 6 animals the operated tissue showed activity that was not synchronous with the rest of the uterus. These data indicate that: (1) isolated uterine muscle in vivo has rhythmicity resembling that of intact myometrium and (2) systemic or local circulating factors are not responsible for synchronizing uterine activity before parturition, although circulating factors do play a major role in increasing the uterine activity which occurs at parturition and at oestrus, and (3) hydraulic continuity between different regions of the uterus is not essential for maintaining co-ordinated activity.

Induction of transient functional luteolysis in cyclic sheep by a 3 beta-hydroxysteroid dehydrogenase inhibitor

The mechanism by which prostaglandin F2 alpha terminates luteal function in the sheep is unclear even though it is used extensively in animal husbandry. At the time of luteal regression, a decrease in 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity is apparent in the corpus luteum, but it is not known whether the decrease in enzyme activity is the primary cause of structural luteolysis. The effect of trilostane, a 3 beta-HSD inhibitor, on luteal function and morphology has therefore been investigated. Intravenous injection of trilostane in the mid-luteal phase of the oestrous cycle caused a decrease in ovarian tissue progesterone content. A transient decrease in peripheral and utero-ovarian vein plasma progesterone was observed but there was no significant effect on the length of the luteal phase of the cycle. There was no significant change in plasma 13,14-dihydro-15-oxo-prostaglandin F2 alpha during the period when plasma progesterone was depressed. Morphological examination of the corpora lutea revealed a decrease in the concentration of electron-dense granules without any other features of impending luteal regression. When plasma progesterone was reduced for more than 10 h by two injections of trilostane 4h apart, there was again no subsequent effect on the length of the oestrous cycle or on the return to oestrus. Plasma progesterone returned to preinjection levels within 24 h of injection. This evidence suggests that competitive inhibition of 3 beta-HSD activity, per se, is ineffective in bringing about structural luteolysis.

Concentrations of prolactin in the plasma of fetal sheep and in amniotic fluid in late gestation and during dexamethasone-induced parturition

The concentration of prolactin in samples of fetal plasma and amniotic fluid collected from sheep with indwelling catheters has been measured by radioimmunoassay. There was considerable variation between animals in the concentration of prolactin in fetal plasma which ranged from less than 2 micrograms/l to greater than 50 micrograms/l. In five out of eight fetuses which were sampled at intervals throughout the last 30 days of pregnancy, there was an increase in the concentration of prolactin in the plasma before parturition. The concentration of prolactin in amniotic fluid was consistently low (approximately 1 microgram/l). Induction of premature parturition by intrafetal infusion of dexamethasone was accompanied by an increase in the concentration of prolactin in only one of three fetuses infused. These results indicated that prolactin is present in fetal plasma but that an increase in prolactin in fetal plasma before the onset of parturition does not always occur. The low concentration of prolactin in amniotic fluid contrasts with the high concentrations of this hormone found in the amniotic fluid of the primate.

The interaction of human endometrial and myometrial steroid receptors with danazol

The affinity of danazol for oestrogen, androgen and progesterone receptors in human endometrium and myometrium was determined, to study the mechanism of action of this drug in the treatment of endometriosis. The ability of danazol to combine with each of the three types of receptor was similar in both endometrium and myometrium. The capacity of danazol to compete with oestradiol-17 beta for the oestrogen receptor was very low (1.72 +/- 0.48 X 10(-3%) cross reaction, mean +/- SEM) and danazol, at the maximum concentration used, was unable to saturate the receptor; but danazol's ability to compete with progesterone for its receptor was considerably higher (8.41 +/- 1.65% using progesterone, 1.95 +/- 0.41% using R5020) and was saturable. Danazol was also able to displace dihydrotestosterone from the cytosol androgen receptor (6.29 +/- 1.82% cross reaction). The association constant of oestradiol for the endometrial and myometrial oestrogen receptors was 2.19 X 10(9)M-1 and 7.45 X 10(9)M-1 respectively, while that of progesterone and dihydrotestosterone for their receptors was similar in endometrium and myometrium (mean 0.25 +/- 0.06 X 10(9) M-1 and 3.62 +/- 1.67 X 10(9) M-1 respectively). Using R5020, the association constant for the myometrial progesterone receptor was 2.50 +/- 0.73 X 10(9) M-1. We conclude that, in view of the high circulating levels of danazol present in patients being treated for endometriosis, it is possible that danazol may bind to, and partly saturate, endometrial and myometrial oestrogen, progesterone and androgen receptors during treatment. An explanation may thus be provided for some of the diverse actions of this drug.

Ovine placental lactogen concentrations during premature delivery induced by infusion of dexamethasone or adrenocorticotrophin to the fetus

Premature delivery was induced by intrafetal infusion of dexamethasone or (1-24)ACTH, starting between days 124 and 129 of pregnancy in twelve ewes carrying intact (n = 7) or hypophysectomized (n = 5) single fetuses. Concentrations of ovine placental lactogen (oPL) in maternal plasma were measured by specific radioimmunoassay before and during premature delivery. There was no significant change in oPL concentrations before delivery in ewes carrying either intact or hypophysectomized fetuses. The results suggest that a prepartum decline in oPL is not an essential prerequisite for delivery, and indicate that fetal glucocorticoids are not directly responsible for the prepartum fall in oPL concentrations observed at spontaneous delivery.