Effects of dihydrotestosterone on progesterone secretion in pseudopregnant rats

To determine if the administration of dihydrotestosterone (DHT) suppresses serum progesterone concentrations in pseudopregnant rats and if so what role the decidua play in mediating this effect, two pellets (8 mg) of DHT were inserted under each ovarian bursa on Day 9 of pseudopregnancy in hysterectomized or intact rats with or without the decidua. The treatment induced within 24 hr a 50% decline in serum progesterone concentrations in decidua-bearing rats only; a further reduction was observed on Days 11 and 12. To further determine if the effect of DHT on serum progesterone concentrations is due to its effect on luteal luteinizing hormone (LH)-receptor content, rats were similarly treated on Day 9 and the capacity of corpora lutea to bind 125I-labeled human chorionic gonadotropin (hCG) on Day 12 in all three groups of rats was examined. DHT treatment had no effect on luteal LH-receptor content in any group. These results suggest that DHT is luteolytic in pseudopregnant rats only in the presence of the decidua and it is speculated that this effect is mediated by suppressing the decidual luteotropin.     

Effect of indomethacin on the progesterone secretion of hysterectomized pseudopregnant rats

The length of pseudopregnancy and the progesterone levels in rats pseudopregnant and hysterectomized on their 2nd day and injected daily with indomethacin (500 g/0.2 ml) from the 2nd to 10th day do not differ from those exhibited by oil treated rats. On the contrary, indomethacin treatment from 11th day on, results in both a lengthening of the diestrous phase and a delayed luteolysis. These findings point out to an extrauterine prostaglandin synthesis mechanism participating in the functional luteolysis in histerectomized pseudopregnant rats.     

Effect of progesterone and oestradiol benzoate on oestrous behaviour and secretion of luteinizing hormone in ovariectomized fallow deer (Dama dama).

Eighteen ovariectomized fallow deer does and two adult bucks were used to investigate the effect of exogenous progesterone and oestradiol benzoate on oestrous behaviour and secretion of luteinizing hormone (LH). In Expts 1 and 2, conducted during the breeding season (April-September), does were treated with intravaginal Controlled Internal Drug Release (CIDR) devices (0.3 g progesterone per device) for 12 days and differing doses of oestradiol benzoate administered 24 h after removal of the CIDR device. The dose had a significant effect on the proportion of does that exhibited oestrus within the breeding season (P less than 0.001), the incidence of oestrus being 100% with 1.0, 0.1 and 0.05 mg, 42% for 0.01 mg and 0% for 0.002 mg oestradiol benzoate. There was a significant log-linear effect of dose on the log duration of oestrus, which was 6-20, 2-14, 2-12 and 2 h after treatment with 1, 0.1, 0.05 and 0.01 mg of oestradiol benzoate, respectively. Dose had a significant effect on the peak plasma LH concentration (P less than 0.01), mean (+/- s.e.m.) surge peaks of 27.7 +/- 2.3, 25.9 +/- 1.8 and 18.6 +/- 3.4 ng/ml being observed following treatment with 1, 0.1 and 0.01 mg oestradiol benzoate respectively. In Expt 3, also conducted during the breeding season, progesterone treatment (0 vs. 6-12 days) before the administration of 0.05 mg oestradiol benzoate had a significant effect on the incidence of oestrus (0/6 vs. 10/12, P less than 0.05), but not on LH secretion. The duration of progesterone treatment (6 vs. 12 days) had no effect on oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oestradiol and progesterone receptors in the pig oviduct during the oestrous cycle

The concentrations of the tissue receptors for oestradiol (E) and progesterone (P) in the porcine oviduct at different stages on the oestrous cycle have been investigated by in vitro binding and exchange methods. Both hormones bound to specific cytoplasmic (Rc) and nuclear (Rn) receptor proteins with high affinity. The concentrations of ERc and ERn were two-fold higher in the ampulla as compared to the isthmus. The amount of ERc in the isthmic portion of the oviduct did not vary throughout the oestrous cycle. However, the ampullar ERc concentrations increased during prooestrus, showed a maximum at standing oestrus, thereafter decreasing. Significant variations in the amount of oviductal ERn were observed. Despite the differences in ERn amounts between segments, the concentration of ERn increased significantly during late prooestrus, attaining a three-fold elevation and remaining elevated during the period of standing oestrous and early luteal phase (days 3-4), thereafter returning to basal levels. No significant variations in the amount of isthmic PRc were found throughout the period studied. The ampulla, however, showed a significant increase in PRc concentrations during standing oestrus, thereafter decreasing. The concentrations of PRn in isthmus and ampulla were of about the same magnitude and varied significantly during the oestrous cycle, increasing in concentration from standing oestrous onwards. The temporal relationships between the variations in levels of oestradiol and progesterone receptors in oviductal tissues and those of the circulating plasma levels were established. The data obtained in this study suggest a relationship between the changes in the levels of oestradiol and progesterone oviductal binding during the first days of the oestrous cycle, and the gamete and embryo transport throughout the oviduct in the porcine species.     

Effect of treatment with progesterone and oestradiol benzoate on ovarian follicular turnover in postpartum anoestrous cows and cows which have resumed oestrous cycles.

Two experiments were carried out to determine the effect of a low dose of progesterone (P) with and without the addition of an injection of oestradiol benzoate (ODB) on ovarian follicle dynamics, oestradiol production and LH pulsatility in postpartum anoestrous cows, compared with cows which had resumed oestrous cycles (cycling cows). In the first experiment, anoestrous Jersey cows were treated with (AN+P, n=8) or without (AN-3, n=3) a previously used intravaginal progesterone releasing (CIDR) device for 10 days, commencing 3 or 4 days after emergence of a new dominant follicle (DF1) as determined by transrectal ultrasonography. Contemporary cycling cows (CYC+P, n=8) were similarly treated with used CIDR devices and injected with prostaglandin F(2alpha) (PGF) at the time of device insertion. Follicle turnover was monitored by daily ultrasonography and pulsatile release of LH was measured on the ninth day after device insertion. During the period of CIDR device insertion, a second dominant follicle emerged in 4/8 of the CYC+P group and 7/8 of the AN+P group (P=0.14). Maximum diameter of DF1 was greater in cows in the CYC+P compared with the AN+P group (P=0.02), but did not differ between cows in the AN+P and AN-P groups (P>0.1). Frequency of LH pulses was greater in cows in the CYC+P than AN+P group (P=0.06), and in cows in the AN+P than AN-P group (P=0.02).In the second experiment, anoestrous (n=20) and cycling (n=11) Friesian cows were treated with a new CIDR device for 6 days commencing 3 days after emergence of a new dominant follicle (DF1). Cycling cows were also injected with PGF on the day of device insertion. Half of the cows in each group were injected with 2mg ODB on the day of device insertion. Daily ultrasonography was used to monitor follicular dynamics throughout the experimental period. Follicular turnover was increased by ODB in cycling (5/5 versus 1/6; P<0.05), but not anoestrous cows (5/9 versus 4/11). Persistence of DF1 was reduced by ODB treatment in both cycling and anoestrous cows (P<0.001). Maximum diameter of DF1 was influenced by ODB treatment and reproductive status (P<0.05). In anoestrous cows in which a second dominant follicle did not emerge during the period of device insertion, the interval from emergence of DF1 to emergence of a second dominant follicle was significantly delayed by treatment with ODB (P=0.04).In conclusion, P treatment of anoestrous cows increased pulsatile release of LH, but did not induce the development of persistent follicles. Injection of ODB in association with P treatment reduced the persistence of dominant follicles in both cycling and anoestrous cows, but delayed subsequent follicular development in a proportion of anoestrous cows.     

Effects of cholesterol and cAMP on progesterone production in cultured luteal cells isolated from pseudopregnant cat ovaries

The present study was designed to incubate luteal cells isolated from pseudopregnant cats and to investigate the effects of cholesterol and cAMP on luteal progesterone production. Corpora lutea were collected from the cats on days 10 and 15 of pseudopregnancy. Luteal cells were isolated from the ovaries by collagenase digestion. Steroidogenic luteal cells were stained for 3β-hydroxysteroid dehydrogenase (3β-HSD) activity. Cells (2 × 10⁴) staining positive for 3β-HSD were cultured for up to 7 days. The cells were treated with 22(R)-hydroxycholesterol (22R-HC) and dibutyryl cyclic AMP (dbcAMP) on days 1, 3 and 7.Treatment of cells with 22R-HC resulted in a dose-dependent increase (p < 0.001) in progesterone production. When 22R-HC was used at a concentration of 10 μg/ml, it resulted in 2.7- and 5.1-fold increases in progesterone production on days 3 and 5, respectively. When the dose was doubled (20 μg/ml), treated cells produced four times more progesterone on days 3 and 7, and three times more on day 5. By day 7, progesterone production increased up to 9.1 times more than the control.Incubation of cells with both concentrations of dbcAMP (0.1 mM and 1 mM) resulted in significant stimulations of progesterone on days 5 and 7 (p < 0.001). However, on day 3, only higher doses of dbcAMP (1 mM) resulted in significant stimulation (p < 0.05). Progesterone production was increased up to 2- and 2.9-fold of the control when cells were treated with lower concentration of dbcAMP (0.1 mM) on days 5 and 7, respectively. Incubation of cells with 1 mM concentrations of dbcAMP induced a 3.2-fold increase on day 5 and a 5-fold increase on day 7.In conclusion, a successful incubation was performed for long-life culturing of luteal cells collected from pseudopregnant cats. The method works well and allows for optimal growth and development of cells in the culture. The present study also demonstrated that incubating cat luteal cells with 22R-HC and dbcAMP induces a significant increase in luteal progesterone synthesis.     

Role of progesterone and oestradiol in the regulation of uterine oxytocin receptors in ewes.

The interaction between oestrogen and progesterone in the regulation of the uterine oxytocin receptor in sheep was evaluated by measuring the binding of oxytocin to membrane preparations of caruncular and intercaruncular endometrium and myometrium. Ovariectomized ewes were assigned in groups of five to each cell of a 4 x 2 factorial design. The four treatments were (a) vehicle (maize oil) for 12 days, (b) progesterone (10 mg day-1) for 9 days, (c) progesterone for 9 days followed by maize oil until day 12 and (d) progesterone for 12 days. The two oestradiol treatments consisted of the administration of implants in the presence or absence of oestradiol. The ewes were killed on day 10 (group b) or day 13 (groups a, c and d) for collection of uterine tissues. The response of the caruncular and intercaruncular endometrium to the treatments was similar. In the absence of oestradiol, treatment with progesterone continuously for either 9 or 12 days reduced the concentration of the oxytocin receptor in comparison with both the control and the progesterone withdrawal group (in which values were similar). The presence of oestradiol reduced the receptor concentrations in control and both 9- and 12-day continuous progesterone treatment groups, but enhanced the concentration in the progesterone withdrawal group. The myometrial oxytocin receptors responded in a similar way to those in the endometrium to progesterone treatment alone, but the addition of oestradiol produced no further effect. In conclusion, progesterone and oestradiol caused downregulation of the endometrial oxytocin receptor. On the other hand, progesterone withdrawal, similar to that which occurs during luteolysis, increased receptor density in the presence of oestradiol. Progesterone may influence the response of the myometrium to oxytocin by causing a reduction in receptor density.     

Cytosol and nuclear levels of thymic progesterone receptors in pregnant, pseudopregnant and steroid-treated rats

Cytosol and nuclear levels of progesterone receptors in rat thymus and uterus were compared in mature Sprague-Dawley rats under a variety of physiological (non-oestrus, oestrus, pregnancy) and experimental circumstances (pseudopregnancy, oestrogen administration, oestrogen plus progesterone administration). Cytosols and nuclear extracts were charcoal treated to remove endogenous steroids, and incubated overnight at 4 degrees C with the synthetic progestin [3H]R5020 +/- greater than 100-fold R5020, in the presence of greater than 200-fold RU26988 (a highly specific synthetic glucocorticoid) to exclude tracer from glucocorticoid receptors. In the various states examined, levels of progesterone receptors in the uterus were an order of magnitude higher (350-1300 fmol/mg protein) than in the thymus (40-140 fmol/mg protein). In contrast, considerable parallelism between uterus and thymus was seen in terms of the effects of the various manipulations upon tissue levels of progesterone receptors, and of their distribution between cytosol and nuclear compartments.     

Interactions between inhibin, oestradiol and progesterone in the control of gonadotrophin secretion in the ewe

Experiments were carried out to test the hypothesis that inhibin and oestradiol act synergistically to inhibit the secretion of FSH, to test for effects of progesterone, and to compare the FSH and LH responses to ovarian feedback. In Exp. 1, with 11 ovariectomized and 12 intact Romanov ewes during the anoestrous season, doses of oestradiol (administered by means of subcutaneous implants) that restored normal LH pulse frequencies were insufficient to restore normal concentrations of FSH. In Exp. 2, with 48 ovariectomized Welsh Mountain ewes during the breeding season, a factorial design with 4 ewes per cell was used to assess the responses in LH and FSH to 3 doses of oestradiol (s.c. implants) and 4 doses of bovine follicular fluid ('inhibin', 0.2-1.6 ml s.c. every 8 h). This was done initially in the absence of progesterone and then after 7 days of treatment with progesterone (s.c. implants). Analysis of variance revealed a significant synergistic interaction between oestradiol and inhibin on the plasma concentrations of FSH. Progesterone had little effect. In contrast, there was a significant synergistic interaction between oestradiol and progesterone on the concentrations of LH. 'Inhibin' also inhibited LH secretion but this effect was independent of the two steroids. We conclude that there are basic differences in the way that ovarian feedback acts to control the secretion of LH and FSH in the ewe. FSH secretion appears to be primarily controlled by the synergistic action of oestradiol and inhibin on the anterior pituitary gland, while the secretion of LH is inhibited during the follicular phase by an effect of oestrogen at pituitary level and during the luteal phase by the synergistic action of oestradiol and progesterone at the hypothalamic level. Inhibin, or another non-steroidal factor in follicular fluid, may also play a minor role in the control of LH secretion.     

Effect of pituitary grafting on ovarian oestradiol secretion in the hypophysectomized chick embryo.

Chick embryos were hypophysectomized by partial decapitation at the stage of 42 h of incubation and grafted with a hypophysis from a 12-days-old donor embryo on the chorio-allantoic membrane at 9 1/2 days. Two days later, their ovary was removed for organ culture and its oestradiol secretion rate was compared to that of the ovary of hypophysectomized, non grafted control embryos. The oestradiol secretion rate in the grafted embryos was almost twice that in the hypophysioprivic embryos and in the range of that in normal embryos. This result suggests that the hypophysis controls oestradiol secretion of the ovary in the 11 1/2-days-old chick embryo.     

Oestrogen and progesterone receptors in chick oviduct chromatin after administration of oestradiol, progesterone or anti-oestrogen.

Oestrogen-primed and withdrawn chicks were injected with oestradiol benzoate, progesterone, and/or the anti-oestrogens tamoxifen and 4-hydroxytamoxifen. Oestrogen receptors were studied in oviduct chromatin solubilized by mild digestion of purified nuclei with micrococcal nuclease. After a single injection of oestradiol benzoate, ultracentrifugation on sucrose gradients of chromatin extracts labelled with [3H]-oestradiol showed two peaks of oestradiol binding sites, sedimenting at 13--14 S and 7--8 S. After repeated injections of oestradiol benzoate, the 13--14 S peak increased more than the 7--8 S peak. After injection of anti-oestrogen alone or together with oestradiol benzoate, no [3H]oestradiol-binding or 4-hydroxy[3H]tamoxifen-binding peaks were detected in the chromatin. Injection of progesterone also produced an increase of the 13--14 S and 7--8 S chromatin oestradiol receptor. Progesterone receptor could only by detected in chromatin early after progesterone administration, and it sedimented in density gradients with the 12 S mononucleosome fraction. Tamoxifen injected together with progesterone gave higher levels of 13--14 S oestrogen binding sites than did progesterone alone. The presence of a 13--14 S peak of oestrogen binding sites in hormonal situations which promote a biological response in the chick oviduct, and the absence of this peak after administration of anti-oestrogens, suggest that this subfraction of chromatin contains elements involved in gene regulation.     

Serum concentrations of oestradiol and progesterone during the normal oestrous cycle and early pregnancy in the lion (Panthera leo)

During a 6-month study period weekly serum samples demonstrated 9 oestradiol surges above 14 pg/ml (range 19-108 pg/ml) among 3 lionesses isolated from male lions. Intervals between peaks ranged from 3 to 8 weeks. Progesterone surges of more than 17 ng/ml (range 17-282 ng/ml) and lasting for 2-6 weeks were recorded after 7 of the oestradiol peaks. Sexual behaviour correlated well with the oestradiol peaks. Except for cornification following oestradiol peaks, there was no obvious vaginal cytology pattern at other times of the cycle. Pregnancy occurred after a 12-h contact with a male during behavioural oestrus. During gestation (108 days) oestradiol values remained low, while progesterone was elevated to 49 ng/ml within 12 h after mating, reaching a peak of 143 ng/ml at the 4th week, and remaining elevated during the next 2 months.     

Relationship between plasma and uterine oestradiol in pseudopregnant rabbits.

Plasma oestradiol concentrations did not change during hCG-induced pseudopregnancy except for a slight increase on Day 18. However, a marked decline was observed in tissue oestradiol on Day 3 whether expressed on the basis of tissue wet weight or protein. The lowest concentration was found at Day 6 but the Day 18 values were comparable to those of untreated controls.     

Serum concentrations of oestradiol and progesterone, and sexual behaviour during the normal oestrous cycle in the leopard (Panthera pardus)

Three mature nulliparous female leopards were studied for 5 years. During three separate 6-month periods serum oestradiol and progesterone concentrations were measured at weekly intervals. Oestradiol was elevated over 21 pg/ml for 54 weeks during these 3 periods, and 36 oestradiol peaks (65.8 +/- 6.3 pg/ml (mean +/- s.e.m.), range 21-172 pg/ml) were identified. Daily frequency of feline reproductive behaviours averaged over each week increased from 1.9 +/- 0.2 (n = 93) during weeks with low serum oestradiol concentrations (less than 21 pg/ml) to 5.3 +/- 0.6 (n = 54) during weeks when serum oestradiol concentrations (greater than 21 pg/ml) were high. Increased serum progesterone concentrations (13-98 n/gml) were observed on 5 occasions in 2 leopards housed together. These presumptive luteal phases lasted from 1 to 5 weeks. Baseline progesterone values were 1.6 +/- 0.4 ng/ml (n = 131). No progesterone increments were observed in isolated animals, and serum concentrations remained at baseline levels. These limited observations suggest that female leopards do not require intromission to induce ovulation and luteal function. The average interval between oestradiol peaks for cycles with no progesterone increment was 3.4 weeks (range 1-6 weeks). The interval for the 3 complete cycles associated with elevated progesterone concentrations was 7.3 weeks. Analysis of sexual behaviours over the 5-year study period revealed no evidence of seasonality in these captive leopards.     

8-hour rhythm of ovarian progesterone secretion in ewe

Pulse character of hormones secretion in the hypothalamus-pituitary-gonads system is a necessary condition of physiological regulation of reproduction. At the same time, the rhythms of ovarian hormones secretion have not been adequately explored. The researches study mainly three sexually mature ewes. The stages of oestrus cycle were determined on behavioral reactions of females in the presence of ram. Blood samples from jugular vein were collected hourly over 24-hour period during follicular (15-16 days), early (3-4 days) and middle (7-9 days) luteal phase of oestrus cycle, pregnancy (40-105 days) and lactation (30-45 days). 27 experiments were performed. Plasma progesterone was determined by enzyme-immunoassay method. There was no diurnal rhythm of ovarian progesterone secretion in ewes. During early and middle luteal phase of oestrus cycle and lactation, an 8-hour rhythm of progesterone secretion was detected. Follicular phase of oestrus cycle and pregnancy were characterized by irregular rises of fluctuations of progesterone level. It seems that the 8-hour rhythm of progesterone secretion during luteal phase and lactation is controlled by action of intraovarian generator of ultradian rhythms.