Nonluteal Ovary Research Articles

156. EFFECTS OF ALBENDAZOLE ON OVARIAN OESTROGEN SYNTHESIS IN THE RAT

Albendazole is a drug commonly used for treatment of helminth infestation in human and livestock populations. Recent studies show that albendazole reduces ovarian follicular fluid oestrogen levels in sheep1, but the mechanism involved is unknown. The aims of this study were to determine whether albendazole exerts similar effects on ovarian oestrogen levels in the rat, and to assess the effects of albendazole on expression of key steroidogenic genes in the rat ovary. Oestrus cycles were continuously monitored in Wistar rats by vaginal smears. Commencing at proestrus, albendazole was administered for 12 days in drinking water (approximate dose 15 mg/kg/day). Plasma and whole ovaries were collected on the fourth proestrus (1500–1600h). A second group of rats were treated similarly except that pseudopregnancy (PSP) was induced by mating with a vasectomised male at the second proestrus. Plasma and the non-luteal ovary were collected on day 8 of PSP. Oestradiol was extracted from plasma and ovaries with ethyl acetate and concentrations measured by a chemiluminescent assay. Expression of steroidogenic acute regulatory protein (StAR), P450 side chain cleavage (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), aromatase and 20α-hydroxysteroid dehydrogenase (20α-HSD) mRNAs were measured by RT-PCR. Oestrus cyclicity, ovarian weight and mating behaviour were all unaffected by albendazole in cycling and PSP rats, although as expected levels of oestradiol were lower in PSP. In ovaries of cycling rats albendazole did not affect oestradiol concentrations but reduced ovarian P450scc mRNA expression (by 65%; P=0.024) and there was a trend for an increase in 3β-HSD (P=0.09) and aromatase expression (P=0.12). Expression of the other steroidogenic genes was unaffected and no changes in gene expression were observed in PSP rats. In conclusion, albendazole treatment reduced ovarian P450scc in cycling rats but did not inhibit ovarian oestradiol synthesis or reproductive function.

In vitro progesterone production by maternal and embryonic tissues during gestation in the southern snow skink ( Niveoscincus microlepidotus)

The southern snow skink, Niveoscincus microlepidotus, has a protracted gestation, lasting approximately one year. Ovulation occurs in spring (November) and embryonic development is completed by early autumn (March); however, birth does not occur until the following spring. Previous studies have shown that plasma progesterone concentration peaks in preovulatory females (spring, October), remains high during early gestation, and decreases to basal by autumn. In vitro progesterone production by corpora lutea, non-luteal ovary, anterior oviduct, placental tissues, muscle, and embryonic adrenal-gonads from N. microlepidotus was assessed throughout gestation. Tissues were incubated with or without the precursor pregnenolone for 3 h at 24 °C; the resulting media were analysed for progesterone using radioimmunoassay. In vitro progesterone production by corpora lutea in media only was high during early gestation, dropping to basal by autumn. Maternal adrenal glands produced progesterone in vitro in media only throughout gestation; however, the pattern of production did not correlate with plasma concentrations and may represent steroid that is normally converted to corticosterone. Non-luteal ovary, anterior oviduct, placental tissues, muscle, and embryonic adrenal-gonads produced minimal progesterone in media only, but were able to convert pregnenolone to progesterone; this suggests steroid metabolic capability within these tissues. Further research is needed to address the possible endocrine role(s) of placental and embryonic tissues during gestation in viviparous squamates.

Spontaneous Termination of an Induced Pseudopregnancy in the Djungarian Hamster, Phodopus campbelli

The mechanisms which underlie the termination of a functional pseudopregnancy and the return to a behavioral estrus in the Djungarian hamster, Phodopus campbelli, were investigated through changes in (1) serum prolactin concentrations; (2) progesterone and estradiol concentrations in the serum and extracted corpus luteam, ovulatory follicle, and non-luteal portion of the ovary; and (3) corpus luteum and non-luteal ovary weight. Females were asynchronous in the timing of resumption of behavioral estrus, ranging between Days 9 and 11 postcoitus with the mode on Day 10. Unlike proestrus of a cycle, mating following a pseudopregnancy was associated with a large surge of progesterone in serum. Early pseudopregnancy was characterized by high pulsatile changes in serum prolactin, stable serum and corpus luteum progesterone, low concentrations of serum and ovarian estradiol, and high, stable corpus luteum weight. Although the day of return to behavioral estrus varied across females, there was synchrony between females in the timing of regression of corpus luteum function and structure. Serum prolactin and progesterone levels significantly decreased by Day 7 but were not followed by a decrease in corpus luteum progesterone content until Day 8. Changes in luteal function were also uncoupled from changes in weight since luteal weight remained high through Day 8 before disappearing from the ovary by Day 9. The pattern and level of prolactin surges during pseudopregnancy is the same as that seen during pregnancy, suggesting that the termination of coitally induced pituitary prolactin surges is spontaneous.

Endocrinology of the pregnant Djungarian hamster Phodopus campbelli.

Factors regulating maternal serum progesterone concentrations during pregnancy in the Djungarian hamster Phodopus campbelli were investigated through changes in (1) concentrations of progesterone and oestradiol in the serum and extracted corpus luteum, non-luteal ovary, and placenta during late pregnancy, (2) prolactin concentrations in the serum, and (3) mass of the fetus, placenta, corpus luteum and non-luteal ovary. Early pregnancy (days 1-4) was characterized by surges of prolactin, corpus luteum growth and increased corpus luteum activity as indicated by increases in luteal mass, progesterone content and serum progesterone concentration. During mid-pregnancy (days 8-11) there was a loss of prolactin surges and a halt in the growth of the corpus luteum, as indicated by stable luteal mass, progesterone content and serum progesterone concentrations that were comparable with those of day 4 of pregnancy. At the same time, the non-luteal ovary began to secrete oestradiol and, on day 12, preovulatory follicles of unknown function were found. During late pregnancy (days 14-17), the prolactin surge pattern was re-established, the non-luteal ovary and corpus luteum contained oestradiol, luteal cell growth caused an increase in corpus luteum size and mass, and serum progesterone concentrations doubled. As late-term pregnancies failed to survive bilateral ovariectomy and the placenta contained little extractable progesterone, it appears that the progesterone of Djungarian hamster pregnancy is synthesized by the corpus luteum throughout gestation.

Preimplantation endocrinology in the Djungarian hamster (Phodopus campbelli): progesterone, estrogen, corpora lutea, and embryonic development. G.

This study reports the results of a detailed investigation of pregnancy in the Djungarian hamster, Phodopus campbelli, with a 2-h time resolution from 2000 h on proestrus (Day 0) through 0600 h on Day 5. Comparisons of the serum levels of progesterone (P4) and estradiol-17 beta (E2), along with the extractable content of each in the corpora lutea and the nonluteal portion of the right ovary, were used to assess the sources and circulating levels of these steroids throughout preimplantation pregnancy. Simultaneous investigation of embryonic development and location within the reproductive tract permitted accurate staging of development. The time course for development and implantation was similar to that in other short-cycle rodents, with transit into the uterus on the evening of Day 3 and implantation beginning early on Day 5 of pregnancy. In three different circumstances, tissue accumulations of steroids were not associated with concurrent increases in serum levels. The first, late on proestrus to early Day 1 of pregnancy, was a significant accumulation of P4 in the nonluteal ovary while serum levels remained basal. The second, throughout Day 2 of pregnancy, was an accumulation of P4 in the corpora lutea that paralleled the pattern of serum P4 during a normal estrous cycle, but which, in these pregnant females, was not seen as elevated serum P4 levels. This response is likely to be coitally induced and thus advances the first maternal steroid response to pregnancy by 24 h relative to other short-cycle rodents studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal vagotomy decreased the number of ova shed and serum progesterone levels on estrus in the cyclic hamster.

The effects of abdominal vagotomy (AVGT) on ovarian function were studied in cyclic hamsters. AVGT significantly decreased the number of ova shed (AVGT: 10.5 +/- 1.5 ova/hamster, sham: 15.8 +/- 0.7 ova/hamster; P less than 0.05) and serum progesterone levels (AVGT: 2.1 +/- 0.3 ng/ml, sham: 3.9 +/- 0.7 ng/ml; P less than 0.05) on the morning of estrus. However, progesterone concentrations in the corpora lutea and non-luteal ovary on estrus in the AVGT and sham groups were similar. The serum estradiol levels in both groups on proestrus increased from 0900 h (AVGT: 75 +/- 10 pg/ml, sham: 72 +/- 6 pg/ml) to 1500 h (AVGT: 204 +/- 27 pg/ml, sham: 196 +/- 35 pg/ml) but there was no significant difference between the two groups. Partial degranulation of ovarian mast cells was not increased in the AVGT group. Also, vasoactive intestinal peptide (VIP) content in the ovary was not increased by AVGT at 0900 h on proestrus (AVGT: 60.1 +/- 16.8 pg/ovary, sham: 37.2 +/- 14.3 pg/ovary). These results indicated that AVGT interferes with normal ovulation and results in an increase in the number of atretic follicles, but that these effects by AVGT seemed not to be mediated through ovarian mast cells and VIP.

Effects of the ovary, sucking stimulus and season on the pattern of LH and FSH release in the female tammar, Macropus eugenii.

The sequential effects of removal of the corpus luteum, removal of the non-luteal ovary and sucking stimulus and the effects of season of the year on the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) have been determined in the tammar wallaby, Macropus eugenii. Plasma concentrations of LH and FSH were measured at 15 min intervals for 6 h in eight animals at four successive times in the breeding season (lactational quiescence); (A) while they were intact and lactating, (B) 10 days after removal of the ovary bearing the quiescent corpus luteum, (C) 21 days after bilateral ovariectomy and (D) 21 days after removal of the sucking stimulus, and (E) in the following non-breeding season (seasonal quiescence). Single blood samples were taken twice weekly during lactational quiescence. In the presence of ovarian tissue, basal concentrations of LH were low (0.94 ng mL-1) with pulses of low magnitude (1.3 ng mL-1) and low frequency (1.4 pulses per 6 h). There was no response to luteectomy but all three parameters increased after bilateral ovariectomy. Removal of the sucking stimulus affected the LH pulse frequency but seasonal differences were not evident. The pattern of release of FSH was not pulsatile. There was no response to luteectomy in basal concentrations of FSH but these rose significantly after bilateral ovariectomy (P less than 0.001) in lactational quiescence. There was no effect of removing the sucking stimulus but in seasonal quiescence concentrations were higher. The results indicate that non-luteal ovarian tissue is essential for the negative-feedback effects on LH and FSH secretion, that the pattern of release of LH, but not FSH, is pulsatile, and that there is no marked seasonal change in hypothalamo-hypophysial activity.

Evolution of lactogen receptors in selected rabbit tissues during pregnancy.

The ontogeny of lactogen receptors in brain, adipose, liver, kidney, adrenal gland, mammary gland, ovarian and uterine tissues of pregnant rabbits was evaluated in this study using 125I bovine prolactin as tracer. Brain and adipose tissues were found to have very low receptor numbers throughout pregnancy (less than 20 fmol/mg of protein), while liver and kidney had higher but constant levels of receptor through the same period (200 and 100 fmol/mg of protein, respectively). Mammary gland and adrenal gland tissues exhibited sharp increases in prolactin binding between 15 and 17 days with both having peak receptor binding at 17 days of around 200 fmol/mg of protein. Ovarian and uterine receptor binding increased slowly after day five of pregnancy and reached peak levels of approximately 225 fmol/mg of protein at day 20. Scatchard analysis of the binding of protein in the tissues having increased binding during the course of pregnancy, revealed that its affinity for sites in these tissues was the same at 5 and 20 days of gestation, indicating the rise in binding to be a result of increased numbers of available receptors. Sub-organ localization studies found the binding of prolactin to adrenal gland, ovary and uterus to be essentially located in adrenal cortex, nonluteal ovary and endometrium. Incubation of membranes from each of the tissues showing significant change during pregnancy, from several time points of pregnancy, with 5.0 M MgCl2 produced little change in apparent receptor numbers; suggesting that receptor occupancy levels of endogenous prolactin was low.

The suppressive effect of the maternal pituitary on relaxin secretion during the second half of pregnancy in rats does not require the presence of the nonluteal ovarian tissue.

This study was conducted to determine whether the suppressive effect of the maternal pituitary on relaxin secretion, luteal growth, and progesterone secretion during the second half of pregnancy in rats (Golos and Sherwood, 1984) requires the presence of the nonluteal ovary. At proestrus, rats received unilateral follicular autotransplants to the kidney capsule. These developed into ectopic corpora lutea (eCL) which maintained pregnancy following removal of the in situ ovary on Day 13 of pregnancy. On Day 8, the conceptus number was left unchanged (eCL-5C) or adjusted to 2 (eCL-2C). Serum relaxin levels, eCL relaxin levels, and eCL weights were significantly lower in eCL-2C rats than in eCL-5C rats from Day 12 through Day 20. Following hypophysectomy on Day 13, serum relaxin levels increased significantly in both groups. Mean luteal weights also increased following hypophysectomy of eCL-2C rats. Although not statistically significant, serum progesterone levels tended to be higher in eCL-5C rats than in eCL-2C rats from Day 12 until Day 18; serum progesterone levels tended to increase following hypophysectomy regardless of conceptus number. It is concluded that the presence of the non-luteal components of the ovary are not required for the suppressive effect of the maternal pituitary on relaxin secretion and luteal growth during the second half of pregnancy.

Timing of the luteal-placental shift in the baboon (Papio cynocephalus).

Normally cycling female baboons (Papio cynocephalus) were mated with males of proven fertility during the periovulatory period. After pregnancy was confirmed, the corpus luteum-bearing ovary was removed (CL-OVX) at day 18 (n = 1), day 20 (n = 4), day 25 (n = 3), or day 30 (n = 4) of gestation. Upon CL-OVX at day 18 or 20, there was an immediate decline in plasma progesterone to basal levels, and pregnancy was not maintained. After CL-OVX on days 25 or 30, there was a transient, small decline in plasma progesterone levels which recovered rapidly to levels found in pregnant controls, and pregnancy was maintained. Only one baboon failed to maintain pregnancy after CL-OVX on day 30, but progesterone levels remained elevated for 3 days before the termination of pregnancy suggesting that causes other than CL-OVX were responsible. In another group of three baboons, depot medroxyprogesterone acetate was administered before CL-OVX at day 20 of gestation and again at days 23 and 26. Progesterone declined sharply after CL-OVX to near basal levels but increased between days 22 and 24, and pregnancy was maintained in all cases. Estradiol levels did not decline as sharply as those of progesterone in any group, which indicates an exclusively luteal source for progesterone while estradiol comes from both the luteal and nonluteal ovaries. There is a placental increase in estradiol production which occurs much later than does the production of progesterone. The luteal-placental shift occurs between day 20 and 25 of gestation in the baboon, earlier than in women but later than in rhesus monkeys.

First luteal tissue in ewe lambs: influence on subsequent ovarian activity and response to hysterectomy.

Two experiments were conducted in peripuberal ewe lambs to determine (a) the influence of the first luteal structure [most frequently a transient (i.e., 1 to 4 d) structure] on subsequent ovarian activity and (b) a role for the uterus in its demise. In Exp. 1, 21 lambs were assigned randomly on the day of the first rise in progesterone in the plasma to (1) sham-operation, (2) removal of the nonluteal ovary, (3) removal of the luteal ovary and (4) removal of the luteal ovary plus progesterone replacement (5 mg given three times 12 h apart, initiated at surgery). No effect of treatment on subsequent ovarian activity was observed. In Exp. 2, four of 14 lambs were assigned randomly to be hysterectomized before their first rise in progesterone. The remaining 10 lambs, (five each) were sham-operated or hysterectomized on the day of the first rise in progesterone. All hysterectomized lambs (N = 9) exhibited a rise in progesterone and maintained elevated concentrations of progesterone, whereas sham-operated lambs initiated estrous cycles. Oviducts and uteri collected from lambs hysterectomized on the day of the first rise in progesterone in Exp. 2 were flushed for presence of oocytes and none were found. Similarly, no retained oocytes were found in histological preparations of first luteal structures obtained from eight lambs ovariectomized in Exp. 1. Concentrations of luteinizing hormone (LH) and prolactin were determined in daily samples collected from 19 lambs in Exp. 1. Luteinizing hormone increased and became more variable as lambs matured, whereas prolactin decreased with no detectable change in variability. It is concluded that the transient luteal structure is not required for sexual maturation and that its lifespan is uterine dependent.

Blood flow in the ovary and adjacent structures of the non-pregnant sheep.

Blood flow of the ovary, vascular pedicle and oviduct was measured in anaesthetized non-cycling and cycling ewes by timed collection of ovarian venous blood. The degree of arterio-venous shunting across the ovary and pedicle was estimated both in vivo and in vitro by perfusing the tissues with 15 +/- 5 micrometers radioactive microspheres. The mean ovarian blood flow in non-cycling animals was 1.9 ml/min, which was 51% of blood flow in the ovarian vein. In cycling animals ovarian blood flow at midcycle was 2.9 ml/min (66% of ovarian venous flow) in non-luteal ovaries and 4.3 ml/min (79% of venous flow) in luteal ovaries. The degree of arterio-venous shunting was low in all stages of the cycle (1.0-2.6% across ovary + pedicle). The degree of shunting was also found to be very small in vitro (0.007-1.38%) in both non-luteal and luteal ovaries. A considerable number of microspheres was entrapped in the vascular pedicle of the ovary indicating the presence of an extensive capillary bed. There was an inverse relationship between blood flow in the ovary and flow in the vascular pedicle. Alterations in distribution of blood flow between the ovary and adjacent structures supplied by the ovarian artery may be of functional significance in allowing rapid changes in ovarian blood flow. The results of the present study indicate that changes in ovarian blood flow during the oestrus cycle are not caused by an action on arterio-venous shunt vessels.

Distribution of visible follicles on the ovarian surface in ewes.

Two studies were conducted to determine the distribution of follicles on the ovarian surface in ewes. In Exp. 1, the effect of the corpus luteum on the distribution of follicles was investigated on d 9, 12 and 14 postestrus in unilaterally ovulating ewes. Follicles (greater than or equal to 2 mm diameter) were inventoried by size and distance from the center of the corpus luteum or corpus albicans. There were more small follicles (less than or equal to 4 mm diameter) on d 9 than on d 12 and 14, Although the ovary bearing the corpus luteum had a greater number of large follicles, no positive relationship of the corpus luteum to the diameter of the closest follicle or the distance of the largest follicle was found. In Exp. 2, follicles were inventoried on ovaries from ewes during the estrous cycle, postpartum anestrus, seasonal anestrus and the peripuberal period. During the estrous cycle, two apparent waves of follicular growth were noted. In addition, during the luteal phase the luteal ovary consistently had a larger follicle than the nonluteal ovary. When estimates were made of the effects of size of follicle on distance of the follicle from the reference structure and of distance on size of follicle, presence of luteal tissue, and day of estrous cycle were found to influence the variances. In addition the interaction of these characteristics affected the variation of size or distance. Weighting the distribution of ovarian structures for relative ovarian mass allowed an examination of localization of structures to standardized ovarian areas. More follicles and corpora lutea were found in the middle of the ovary than on the ends. Although the numbers of follicles in a standardized area were correlated with ovarian mass, occurrence of corpora lutea in a standardized area was not significantly correlated with ovarian mass. Collectively, these results are indicative of a local effect by the corpus luteum on the diameter of the largest follicle and a systemic effect on the number of follicles. In addition, because specific regions appear to be more favorable for follicular activity and ovulation, a precise local effect of the corpus luteum is difficult to determine.

In vivo and in vitro ovarian steroidogenesis in the long term hypophysectomized rat.

Ovarian steroidogenesis in the hypophysectomized rat was studied using immature female rats pretreated with 5 IU PMS at 30 days of age and hypophysectomized between 0900–1000 h on either day 32 (before ovulation; group without corpora lutea) or day 33 (the day of ovulation; group with corpora lutea). Serum levels of progesterone (P) and estradiol-17β (E2) in the group with corpora lutea were consistently low, but detectable, from day 5–40 after hypophysectomy, whereas serum 20α-dihydroprogesterone (20α-OHP) and testosterone (T) remained relatively high. However, serum P, 20α-OHP, T, and E2 in the animals without corpora lutea were significantly less on days 5–20, suggesting that these hormones were primarily secreted from corpora lutea but not nonluteal ovarian tissues. The steroidogenic capacity of the corpora lutea and nonluteal ovary at different times after hypophysectomy was assessed by incubation for 2 h in Krebs-Ringer bicarbonate. Five to 40 days after hypophysectomy, the corpora lutea in vitro pr...

Postovulatory steroidogenesis after PMS-induced ovulation in immature female rats.

Thirty-day-old rats given a single subcutaneous injection of 5 IU pregnant mare serum gonadotropin (PMS) at 0900 h ovulated on the morning of day 33 (= estrus). However, the second ovulation did not occur until 9.4 days later. To determine the mechanism responsible for the delay in the second ovulation, in vivo and in vitro determinations of steroid and peptide hormones were compared between PMS-primed immature rats and adult cyclic rats. In PMS-primed rats, the corpora lutea (CL) produced progesterone for 2 days longer (until day 36) than the CL of the adult rat. Serum levels of 20 alpha-dihydroprogesterone, testosterone, and estradiol in PMS-primed rats were significantly lower than the corresponding values in adult rats. Serum LH was consistently lower in the PMS-primed rats. An increase in serum FSH occurred on days 36-37, which may be responsible for maturation of the follicles destined to ovulate at the second ovulation. On day 37, the nonluteal ovary of the PMS-primed rats also began to produce in vitro appreciable amounts of testosterone and estradiol. These findings suggest that the greater levels of prolactin and/or low levels of luteinizing hormone during estrus in PMS-primed rats may be responsible for the prolonged secretion of progesterone by the CL. This in turn inhibits follicular maturation, indirectly by lowering serum LH, which is reflected in reduced ability of the follicles in vitro to produce testosterone and estradiol until the CL regress.

Acute effects of an antiserum to luteinizing hormone on ovarian steroidogenesis in the pregnant rat.

Pregnant rats were injected s.c. at 09.00 h on day 8 of pregnancy (day 1 = sperm-positive vaginal smear) with either 0.2 or 0.5 ml equine antiserum to bovine LH (anti-LH) while control rats were injected with 0.5 ml normal horse serum (NHS). Rats were decapitated 1, 3, 6, 24 and 48 h later and serum was saved for radioimmunoassay of progesterone, androstenedione, testosterone, oestrone and oestradiol. One ovary was kept for histology, and from the other, corpora lutea (three/animal) and the non-luteal ovary (ovarian remnant from which all corpora lutea were removed) were saved for steroid determinations. The production rate of steroids by the luteal and non-luteal ovarian compartment was assessed by incubation in Krebs--Ringer bicarbonate buffer for 2 h. A significant decrease in the serum concentrations of all steroid hormones was induced by 6 h after treatment with anti-LH; progesterone being the first hormone to be consistently reduced (by 3 h). The steroid concentrations remained lower than those in control rats on days 9 and 10. A single injection of anti-LH reduced the number of health antral follicles by 3 h but there were always two to four normal antral follicles per ovary on days 8-10. The initial hormonal changes in the non-luteal ovary after LH deprivation were decreases in the concentration and production rates of the androgens and oestrogens. The initial concentration of non-luteal progesterone was lower 3 and 6 h after anti-LH than in control rats. Although anti-LH induced a decrease in the serum concentration of progesterone 24 and 48 h later, the corpora lutea contained more progesterone on day 8 and produced in vitro more progesterone than controls on day 8 after 0.2 and 0.5 ml anti-LH and on day 9 when only 0.5 ml was give. The increase in the initial concentration of progesterone on day 8 probably represents accumulation resulting from inhibition of luteal progesterone release. It appears, therefore, that the initial alteration after LH deprivation is inhibition of the release of luteal progesterone and this alone is sufficient to account for the interruption of pregnancy. The in-vivo increase in luteal steroidogenesis following LH deprivation was observed to some extent with androstenedione bu testosterone was unaffected. Luteal aromatizing enzymes appeared to be very sensitive to LH deprivation on day 8 since the concentration and production of oestrogen decreased without concomitant decreases in androgen. Progesterone (4 mg) administered along with 0.2 ml anti-LH on day 8 prevented luteal regression and the corpora lutea synthesized progesterone and androgens similarly to NHS-treated controls; however, the corpora lutea of the progesterone-treated group contained and produced less oestrogen than controls.

Antiluteinizing Hormone: Acute Influence on Steroid and Gonadotropin Levels and Follicular Development in the Pregnant Hamster*

Pregnant hamsters were injected at 0900 h on day 4 or 8 (day 1 of pregnancy = sperm-positive) with 0.1 ml of either normal horse serum (NHS) or equine antibovine LH (ALH) and decapitated 1, 3, 6, 12, 18, and 24 h later. Serum was saved for RIA of FSH, PRL, progesterone (P), testosterone (T), and estradiol (E2). Corpora lutea (CL) and nonluteal ovary (NLO) were saved for steroid determinations, and one ovary was saved for histology. Regardless of the day of treatment, ALH induced an immediate decline within 1 h in the serum and luteal E2 concentrations without altering T. At 24 h after ALH, levels of T and P in CL and sera were lower than NHS controls. In NLO, T and E2 declined simultaneously within 1 h after ALH without changing P. Within the next 3–6 h, P in NLO declined to half that of NHS pregnant controls and all antral follicles showed initial signs of atresia. Collectively, these results indicate that, after LH deprivation, the initial hormonal change is a concomitant decrease of E2 in serum, CL, andLO, suggesting that LH is necessary for E2 secretion and maintenance of antral follicles in the pregnant hamster and that decreases of P in serum, CL, and NLO lag behind changes in E2. A dramatic increase in serum FSH-like material accompanied the declines in serum P and E2 after ALH treatment, suggesting that lack of steroid negative feedback at the hypothalamicpituitary axis induces hypersecretion of FSH. A large dose of ALH (0.4 ml) induced a more prompt decline in serum P than 0.1 ml ALH, indicating that a greater degree of LH deprivation may occur sooner with 0.4 ml than with 0.1 ml ALH. Unlike the hysterectomized pseudopregnant (HSP) rat, ALH on day 8 of HSP in the hamster induced a terminal decline in serum P within 24 h. In contrast, the pregnant hamster on day 8 exhibited a more gradual decline in serum P than that observed in the HSP hamster, suggesting that placental factors may be exerting luteotropic actions at this time. The results indicate that luteal aromatizing enzymes appear highly sensitive to LH deprivation since, within 1 h after ALH, luteal E2 concentrations decline without a concomitant decrease in T.

Steroid and gonadotropin levels during the luteal-follicular shift of the cyclic hamster.

This study was designed to correlate ovarian and hormonal changes of cyclic hamsters during the period of luteal regression and rising dominance of antral follicles. Cyclic hamsters (8/group) were decapitated at 2 h intervals between Day 2 at 1000 h and Day 3 at 1000 h; Day 1 is defined as the day of ovulation. Serum was collected for RIA of gonadotropins and steroids. From 1 ovary, corpora lutea (CL) and the nonluteal ovary (NLO) were saved for steroid RIA and the remaining ovary was prepared for histology. The diameter of antral follicles steadily increased from 389 to 437 im during Days 2-3, and the number/ovary increased from 3 at 1000 h Day 2 to 11 at 2400 h Day 2. However, by 1000 h Day 3 the number of antral follicles had declined to 5/ovary. The highest level of serum progesterone (P) occurred at 2000 h Day 2; thereafter, the levels declined abruptly to less than 1 ng/ml by 0400 Day 3. The concentration of luteal P decreased gradually between 2000 h Day 2 and 0400 h Day 3 2 h later there was a drastic decline correlating with an influx of leukocytes into the CL. On Day 2, although antral follicles were present, serum estradiol (E2) was very low. However, estradiol increased at 0400 h Day 3 associated with increased concentration of E2 and androgen in NLO. During the 24 h period, the most striking difference in serum levels of FSH, LH and prolactin was the peak of all 3 hormones at 2200 h Day 2, 4 to 6 h before any significant changes in the serum levels of P or E2. The results demonstrate that the shift from the luteal phase to the follicular phase is a gradual process involving concomitant declining levels of P and increasing levels of E2. The results suggest that the transitory increase of gonadotropins and/or declining levels of P are causally related to enhanced follicular secretion of E2 and androgen.