The role of decidual tissue in the development of the dependency on luteinizing hormone in the rat corpus luteum

In pregnant rats, treatment with an antiserum to LH (LHAS) on days 2-5 inclusive (early LHAS treatment; day 1 = insemination) delayed implantation by about 4 days. The appearance of the dependency of the corpora lutea on LH for the maintenance of progesterone secretion (LH dependency), as determined by the rate of fall in progesterone secretion after a single test injection of LHAS, was also delayed by 4 days. Treatment with a small amount of estradiol on either day 4 or days 4-9 prevented the delay in both implantation and LH dependency. Implantation thus prevented early LHAS treatment from delaying LH dependency, but its effect seems to have been due to decidualization, which accompanies implantation in the rat. In decidual tissue (DT)-bearing pseudopregnant rats, early LHAS treatment delayed LH dependency for only 1 day, while it delayed LH dependency for at least 3 days in ordinary pseudopregnant rats and for at least 4 days in hysterectomized pseudopregnant rats. Estrogen itself seems to have prevented the delay in LH dependency only by inducing implantation, since it had no effect in the DT-bearing pseudopregnant rats. How DT affects the corpus luteum's dependency on LH is unknown, but it may be related to whatever effect DT has on prostaglandin production in the endometrium.     

Pituitary regulation of corpus luteum progesterone secretion in cyclic rats

Pituitary LH and PRL secretion during the early postovulatory period of the rat estrous cycle seem to affect the corpus luteum (CL) autonomy to secrete progesterone. Thus, while PRL would act luteotropically, LH would be luteolytic. To further investigate these facts, 4-day cyclic rats, treated with either 1 mg bromocriptine (CB) or 0.25 ml 70% ethanol (ETOH) at 1600 h on estrus, were injected with 0.5 ml of either an anti-LH serum (LHAS) or normal horse serum (NHS) at 0800 h on metestrus. Rats treated at 0800 h on metestrus with both, CB and LHAS, were also used. To verify through a different procedure the effect of LH and/or PRL deprivation in estrous cycle CL progesterone secretion, hypophysectomy (HYPOX) and sham HYPOX (SHAM) were done at 0800 h on metestrus in either CB- or ETOH-injected rats at 1600 h on estrus. Hypophysectomized rats at 1600 h on estrus were also used. Progesterone secretion was prolonged up to 0800 h on diestrus in those rats deprived of LH from 0800 h on metestrus (ETOH/LHAS, -/CB + LHAS, ETOH/HYPOX) compared with controls (ETOH/NHS, ETOH/SHAM). This luteotropic effect was absent in those rats lacking estrous afternoon PRL (CB/LHAS, CB/HYPOX, HYPOX/-). No effect on CL progesterone secretion was detected in those rats exclusively deprived of PRL on the afternoon of estrus (CB/NHS, CB/SHAM). These results suggest that in the absence of the protective effects of PRL secretion on the afternoon of estrus, rat CL become extremely sensitive to the luteolytic effects of early diestrous LH levels, and this results in 4-day estrous cycles.     

Influence of litter size on antepartum serum relaxin and progesterone immunoactivity levels and on birth in the rat

In the rat, the antepartum elevation of serum relaxin levels consists of two phases separated by a 24-h interval. The second phase, which occurs between 36 and 24 h before birth, is temporally closely associated with functional luteolysis. Relaxin levels then decline throughout the last approximately 24 h of pregnancy. We have postulated that the two phases in the antepartum elevation of serum relaxin levels may be indicative of an increasingly effective endogenous circadian luteolytic process. There is limited evidence that both luteolysis and birth are delayed in rats with small litters. The present study investigated in detail the relationship between litter size and the timing of both functional luteolysis and birth in rats. The number of conceptuses (C) in Sprague-Dawley-derived rats was surgically adjusted on day 8 of pregnancy (day 8) so that rats bore one, two, three, five, or a full complement (FC) of eight or more C. Rats were maintained under a photoperiod regimen of 14 h of light and 10 h of darkness (lights on from 2100-1100 h) beginning on day 8 and observed for birth at 10-min intervals from 2100 h on day 22. Serum levels of both relaxin and progesterone were determined in blood samples obtained at 4-h intervals from 2400 h on day 19 until birth. Ninety-five percent of the rats that had five or more C gave birth during the light phase on day 23, which was designated the normal birth interval. However, only 20% of the rats with three C or less, gave birth during the normal birth interval, and 47% gave birth about 24 h later during the light phase on day 24, which was designated the late birth interval. The 24-h delay in birth of rats with small litters which delivered during the late birth interval appears to be attributable to a delay in functional luteolysis; the antepartum decline in serum relaxin and progesterone levels occurred about 24 h later in these rats than in rats that delivered during the normal birth interval. It is concluded that the C may be associated with the luteolytic process and thereby influence the time of birth in rats. Additionally, the results of this study are consistent with our hypothesis that there is an endogenous circadian luteolytic process in rats during the antepartum period.     

Divergent effects of antiprogesterone, RU 486, on progesterone, relaxin, and prolactin secretion in pregnant and hysterectomized pigs with aging corpora lutea

Porcine corpora lutea produce progesterone and relaxin during pregnancy and after hysterectomy. Peak amounts of relaxin are released into peripheral blood in both pregnant and hysterectomized animals on about day 113 (estrus = day 0 and term = 114), and this release coincides with an abrupt decrease in the progesterone concentration. RU 486, a progesterone receptor antagonist, was used to investigate the effects of interruption of progesterone binding to its receptor on luteal function and gonadotropin secretion of pigs with aging corpora lutea. RU 486 was administered orally to hysterectomized gilts (surgery on day 8) once a day (0800 h) on days 111-115 at two dosages (group 1, 2 mg/kg BW; group 2, 4 mg/kg BW). During 5 days of RU 486 treatment, plasma progesterone concentrations in both treated groups were markedly elevated (32 and 37 ng/ml for groups 1 and 2) compared with 22 ng/ml in the controls (group 3; P less than 0.01). PRL concentrations increased in both groups (9 and 13 ng/ml) and differed significantly from those of the controls (3 ng/ml) (P less than 0.04). RU 486 treatment delayed the time of relaxin peak to days 116.1 and 117.0 in groups 1 and 2 compared with day 114.1 in the controls (P less than 0.01). Pregnant gilts received RU 486 orally once a day (0800 h) at 4 mg/kg BW beginning on day 111 until parturition occurred. Parturition was induced on day 112.7 after only two RU 486 treatments compared with day 114.7 in the control group (P less than 0.01). Progesterone decreased abruptly from a pretreatment mean of 11 to less than 0.6 ng/ml during the 2 days that RU 486 was given compared with a shift from 12 to 6 ng/ml during the same period in the controls (P less than 0.01). The time of the relaxin peak was advanced to day 112.1 in RU 486-treated gilts compared with day 113.9 in the controls (P less than 0.01). Results from this study provide strong evidence that the antagonistic effect of RU 486 on progesterone receptor results in an abrupt increase in PRL and progesterone secretion in hysterectomized gilts with aging corpora lutea. In marked contrast with hysterectomized animals, the acute luteolytic effects of RU 486 depend on the presence of the uterus and/or conceptuses in the pig. Disruption of the regulatory loop of progesterone secretion by RU 486 alters the ability of corpora lutea to produce and release peak quantities of relaxin.     

Comparison of plasma progesterone profiles in cyclic, pregnant, pseudopregnant and hysterectomized pigs between 8 and 27 days after oestrus

Plasma progesterone concentrations were compared in cyclic (n = 12), pregnant (n = 12), oestradiol-induced pseudopregnant (n = 12) and hysterectomized gilts (n = 10) between days 8 and 27 after oestrus. The results were grouped into periods covering days 8-13, 14-20 and 21-27 and analysed by least-squares analysis of variance. Plasma progesterone concentrations were significantly (P less than 0.001) higher in hysterectomized compared with other groups between days 8 and 13. Progesterone concentrations declined rapidly after day 14 in cyclic females and gradually in the other groups. Throughout the third and fourth weeks the mean progesterone concentrations for hysterectomized animals were consistently higher than for pseudopregnant animals (P less than 0.05). The pregnant group means were below but not significantly different from the hysterectomized means in both of the last two periods. The greater progesterone concentrations in hysterectomized gilts indicated that secretion is high without any conceptus-produced or -mediated luteotrophic, and corpora lutea in cyclic, pregnant or pseudopregnant gilts may never reach full secretory potential.     

Indomethacin treatment prevents prolactin-induced luteolysis in the rat

Adult female rats were hypophysectomized and their pituitary glands autotransplanted beneath the left kidney capsule on day 2 (day 1 was the day of ovulation). In such rats the pituitary secretes prolactin fairly constantly and the corpora lutea secrete progesterone for several months. To induce the luteolytic effect of prolactin the rats were first injected s.c. with 2-bromo-alpha-ergocryptine (CB-154) on cycle days 12, 13 and 14 (i.e. 10, 11 and 12 days after operation) to depress prolactin secretion, and then with CB-154 vehicle (70% ethanol) daily until cycle day 21, to allow prolactin secretion to resume. One ovary was removed from each rat on day 15 and the remaining one on day 22. The mean (+/- S.E.M.) weight of the corpora lutea on day 15 was 1.46 +/- 0.06 mg and 0.98 +/- 0.07 mg on day 22 (n = 17). In contrast, rats in which the CB-154 treatment was maintained to day 21 had corpora lutea which weighed 1.31 +/- 0.09 on day 15 and 1.47 +/- 0.08 mg on day 22 (n = 15). To investigate whether indomethacin, a prostaglandin synthesis inhibitor, affected the luteolytic action of prolactin, the experiment was repeated, but on day 15 (after the removal of one ovary) the groups in which CB-154 treatment was stopped, as well as the group in which CB-154 treatment was maintained, were each divided into two groups. In one, indomethacin-containing silicone elastomer wafers and, in the other, blank silicone elastomer wafers, were placed within the bursa of the remaining ovary.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of an antiprogesterone (RU486) on the hypothalamic-hypophyseal-ovarian-endometrial axis during the luteal phase of the menstrual cycle

The impact of the antiprogesterone RU486 [17 beta-hydroxy-11 beta-(4-dimethylaminophenyl) 17 alpha-(1-propynyl)estra- 4,9-dien-3-one] on the hypothalamic-pituitary-ovarian-endometrial axis was examined in normal cycling women during the mid (MLP)- and late (LLP) luteal phases. During the MLP, 10 women received 3 mg/kg RU486 for 3 days. During the LLP, a single dose of 600 mg RU486 was administered to 4 women, and in another 4 women a single dose of 3 mg/kg was given during corpus luteum rescue by hCG. Longitudinal studies with daily and frequent blood samples (every 10 min for 10 h) were conducted during 3 consecutive cycles (control-treatment-recovery). During the MLP, RU486-induced uterine bleeding occurred in all 10 women 36-72 h after the first dose. No histological evidence of endometrial breakdown was found in endometrial biopsies taken 12-24 h before the onset of bleeding. Significant decreases in LH secretion (P less than 0.001) and LH pulse amplitude (P less than 0.006) and blunted pituitary responses to GnRH (P less than 0.01) were evident by the last treatment day, but LH pulse frequency did not change. Complete luteolysis occurred in 2 of the 10 women. Incomplete luteolysis occurred in 8 women and was associated with an initial decline of serum estradiol (P less than 0.001), but not progesterone levels, followed by rebound increases (P less than 0.001) in LH, estradiol, and progesterone levels 3 days later, which may have reversed the luteolytic processes and prolonged corpus luteum function. Spontaneous luteolysis ensued 3-5 days later with the onset of second episodes of uterine bleeding. For serum FSH, an early rise occurred during the luteal phase in advance of the onset of the second episodes of uterine bleeding. This rise may have resulted in early follicle recruitment and accounted for the shorter duration of the follicular phase during recovery cycles. During the LLP, the single RU486 dose resulted in significant decreases in LH pulse amplitude (P less than 0.03), frequency (P less than 0.05), and secretion (not significant) within 12 h. The recovery cycle was entirely normal. Corpus luteum rescue with incremental doses of hCG did not prevent uterine bleeding after RU486 treatment. These findings indicate that RU486 operates at multiple sites and implies that progesterone is important in the control of luteal function. Further, our data provide a basis for exploring the potential use of RU486 as a once a month birth control agent.     

The luteotrophic action of decidual tissue: the stimulating effect of decidualization on the serum progesterone level of pseudopregnant rats.

On day 5 (4th diestrous day), pseudopregnant rats were arranged in pairs, one member of which was subjected to hysterectomy (H-ect) and the other to uterine scratching to induce formation of decidual tissue (DT). Blood samples were collected from each pair of rats immediately before and at various intervals after operation until day 13, and with very few exceptions were assayed for progesterone by CPB in the same assay. From 21 such pairs, the following findings emerged: During the period from day 7-day 11 inclusive, a DT-bearing rat's serum progesterone level was higher than that of its H-ect paired control in 79% of the paired comparisons; the mean serum progesterone level of the DT-bearing rats was higher than that of the H-ect rats on each day during this period; and the progesterone level group mean for all the DT-bearing rats during this period was at least 25% (P less than 0.05) higher than that of the H-ect rats. On days 6, 12, and 13, however, no significant differences were found between the 2 groups by any basis of comparison. Ordinary pseudopregnant rats (subjected only to 1aparotomy on day 5) and rats subjected to uterine scratching which failed to form DT had progesterone levels below or similar to, respectively, those of the H-ect members in the pairs. The findings were interpreted as evidence that DT increases the rate of progesteron secretion.     

A luteotrophic action of prolactin: suppression of intraluteal prostaglandin production or effect?

Adult rats were hypophysectomized and their pituitary glands autotransplanted on day 2 of an estrous cycle (day 1, ovulation); the rats were either hysterectomized or sham hysterectomized immediately before this operation. On day 21, a few days after the beginning of the 3+ month period of regression of progesterone secretion, they were injected sc with 500 micrograms prostaglandin F2 alpha (PGF2 alpha) either on day 21 alone, on days 21 and 22, on days 21, 22, and 23, or on days 21 and 23; controls were injected with saline on days 21, 22, and 23. In the latter the serum progesterone level slowly fell, as it does in untreated rats subjected to pituitary autotransplantation on day 2. PGF2 alpha treatment induced a rapid, drastic fall in the progesterone level, but in each group except the one injected on days 21 and 23, the level returned to, or close to, the control level in about 10 days. Even in the group injected on days 21 and 23, the pattern of serum progesterone resembled the others although the values were much lower. In a similar group of rats subjected to pituitary autotransplantation on day 2 (all of which were also hysterectomized on day 2), a single injection of 500 micrograms PGF2 alpha (which again induced the same changes in serum progesterone as in the first experiment) was combined with either a 6-h or 4-h withdrawal of PRL; this was achieved by injecting 2 bromo-alpha-ergocryptine (CB-154) at zero time to lower PRL secretion, and beef PRL, in a delaying vehicle, 6 or 4 h later, followed by a second dose of PRL 18 h after the first. When combined with such a brief period of PRL withdrawal, the PGF2 alpha treatment induced a very rapid, drastic and permanent fall in serum progesterone, equal to that induced by CB-154 alone, or by removing the pituitary transplant on day 21. The brief periods of PRL withdrawal, by themselves had very little (6 h) or no (4 h) effect on the progesterone level, and treatment with PRL alone was also without effect. Treatment with CB-154, PGF2 alpha, and PRL simultaneously (i.e. without a period of PRL withdrawal) had the same effect as treatment with PGF2 alpha alone.(ABSTRACT TRUNCATED AT 400 WORDS)     

The pattern of progesterone secretion in hypophysectomized rats bearing pituitary transplants: effects of hysterectomy, estrogen, and indomethacin

Cyclic rats were hypophysectomized and their pituitaries transplanted beneath the kidney capsule on day 2 (day 1, ovulation); they were then either hysterectomized or sham hysterectomized (uterus intact rats) and injected sc daily with either 1.0 micrograms 17 beta-estradiol (E1) or with the sesame oil vehicle until autopsy on day 105. Blood samples were drawn by jugular venipuncture every 2 to 3 days until day 21 and once weekly thereafter. In these rats the serum progesterone level rose until about day 8 and tended to reach a plateau between days 8 and 14. The regression phase began, in general, after days 8 to 14 and continued, without change in rate, for at least 3 months. In both the uterus-intact and the hysterectomized rats, E1 seemed to induce an earlier onset of regression and a brief increase in its rate, but did not otherwise affect the rate of regression. In the hysterectomized rats regression began later than in the uterus-intact rats, but its rate was also not different from the latter. The serum progesterone pattern of rats subjected to pituitary autotransplantation on day 2 was compared with that of pseudopregnant rats which were either subjected to pituitary autotransplantation on day 2, 5, 7, or 9, or were given a pituitary homotransplant on day 2, and then hypophysectomized on day 2, 3, 5, or 7. A group of rats with sham operations served as additional controls. In these rats, the same pattern of serum progesterone already described was seen in those subjected to either pituitary autotransplantation on or before day 5, or to pituitary homotransplantation, and to hypophysectomy on or before day 5. However, when the pituitary was autotransplanted on day 7 or day 9, or when the pituitary homotransplant-bearing rat was hypophysectomized on day 7, regression began earlier and was more rapid than in rats operated on on or before day 5. In fact, in the rats operated on on day 9, regression was as rapid as it was in the intact (sham operation) controls. Another group of rats subjected to pituitary autotransplantation and hysterectomy on day 2 was divided into four subgroups on day 21. In two of these, the rats received indomethacin-containing Silastic capsules inserted into each ovarian bursa; in the other two groups blank capsules were similarly inserted.(ABSTRACT TRUNCATED AT 400 WORDS)     

Relationship of estradiol to luteal function in the cycling baboon

Since exogenous 17 beta-estradiol (E2) is luteolytic in some primates, it is reasonable to conclude that endogenous E2 is the naturally occurring luteolytic substance. However, a link between endogenous E2 and spontaneous luteolysis has not been demonstrated. In an attempt to understand the function of E2 in spontaneous luteolysis, we employed the antiestrogen clomiphene. We administered E2, clomiphene, or E2 plus clomiphene to baboons during the luteal phase and measured systemic levels of estrone, E2, progesterone (P), and LH, E2 alone depressed the concentrations of P and bioassayable LH prematurely. The length of the luteal phase was significantly shortened (12.8 +/- 0.9 vs. 15.8 +/- 0.4 days for sham controls; P less than 0.01). Clomiphene blocked the luteolytic effect of exogenous E2, resulting in P levels which were not significantly different (P greater than 0.01) from control and a luteal phase of normal length (15.0 +/- 1.0 days). Treatment with E2 alone caused serum LH concentrations to decrease. The administration of clomiphene alone maintained circulating LH at early to midluteal phase levels but did not alter luteal phase P concentrations or prolong the length of the luteal phase (15.6 +/- 0.4 days). The results suggest that E2-induced luteolysis is a result of the withdrawal of luteotropic support from the (corpus) luteum, while spontaneous luteolysis is a result of some other mechanism which may not involve endogenous E2.     

Interrelations of the renal kallikrein-kinin system and renal prostaglandins in the conscious rat. Influence of mineralocorticoids.

To investigate possible relationships between mineralocorticoids, the renal kallikreinkinin system, and renal prostaglandins, we studied the effects of aldosterone and deoxycorticosterone acetate (DOCA) and of an inhibitor of kallikrein, aprotinin, on the urinary excretion of kallikrein and prostaglandin E-like substance (PGE) by the conscious rat. Aldosterone (0.25 mg/day, sc), injected into six rats for 14 consecutive days, increased PGE and kallikrein excretion from 52.3 +/- 8.7 (mean +/- SE) ng/day and 29.8 +/- 3.0 U/day to 141.5 +/- 30.7 ng/day (P less than 0.02) and 105.6 +/- 28.1 U/day (P less than 0.05), respectively. Similarly, injections of DOCA (5 mg/day) into 14 rats increased the excretion of PGE and kallikrein, measured before and after 10 days of treatment, from 41.6 +/- 3.9 ng/day and 39.4 +/-4.9 U/day to 194.3 +/- 20.7 ng/day (P less than 0.001) and 90.6 +/- 14.7 U/day (P less than 0.001), respectively. Injections of aprotinin for 4 days (50,000 KIU twice daily, sc) in conjunction with DOCA into eight rats pretreated with the steroid for 10 days decreased the urinary excretion of kallikrein and PGE, measured on the 4th day of aprotinin administration, by 61% (P less than 0.01) and 80% (P less than 0.001), respectively. Urinary potassium excretion decreased throughout the course of aprotinin treatment, whereas sodium excretion and urine volume decreased during the first 2 days but subsequently returned toward control values. This study demonstrates that mineralocorticoids enhance the urinary excretion of PGE, and this effect appears to be a consequence of activation of the renal kallikrein-kinin system by the steroids. Thus, changes in the intrarenal activity of the kallikrein-kinin system may modulate renal prostaglandin release.     

The fate of corpora lutea in the cyclic golden hamster

Structural luteolysis shows striking interspecies differences. Morphological changes in the corpus luteum (CL) of the cyclic hamster have been studied alongside the potential involvement of known luteolytic hormones. Ovaries from intact Syrian golden hamsters killed at 1100 h on days 1 and 2 and at 1100 and 1700 h on days 3 and 4 of the estrous cycle were dissected for histological study. The day of ovulation, the day of estrus, was arbitrarily designated day 1 of the estrous cycle. Steroidogenic cells in the CL were scarcely luteinized on day 1 and reached full luteinization on day 2. On the morning of day 3, initial regressive changes (accumulation of lipid droplets, invasion by neutrophils, and accumulation of phagocytic cells) were observed. These regressive changes increased progressively and apoptotic cells as well as phagocytic cells containing phagocytized apoptotic cells were abundant on the evening of day 3. On the morning of day 4, apoptotic cells/bodies and phagocytic cells containing phagocytized material were extremely abundant throughout the CL. However, steroidogenic cells with intact nuclei and well-preserved blood vessels were also found. Surviving cells in the CL showed progressive morphological changes. These cells showed morphological features intermediate between luteal and interstitial cells in the evening of day 4 and were virtually indistinguishable from interstitial cells on day 1 of the following cycle. Additional animals were injected at 1100 h on day 2 with: (a) the dopaminergic agonist CB154 (0.4 mg) to block prolactin secretion, (b) the anti-estrogen LY117018 (1.6 mg) or the anti-androgen Flutamide (3 mg) to block estrogen or androgen receptors, respectively, and (c) progesterone (2 mg) to prevent the fall in serum progesterone concentrations. Ovaries from these animals were collected at 1700 h on day 3 and at 1000 h on day 4. The luteolytic process was not affected by any treatment. These data indicate that, in contrast to its close relatives (e.g., the rat), structural luteolysis in the hamster is independent of the apoptotic inducing luteolytic hormones. In addition, differences in the cellular mechanisms responsible for CL elimination were also present. In the hamster, part of the luteal cells do not undergo apoptosis and seemed to progress through another developmental path giving rise to interstitial-like cells.     

The differential effects of thyroid and gonadal hormones on substance P content in the anterior pituitary of the prepubertal rat

The effects of thyroid and gonadal status on the content of substance P in the anterior pituitary (AP-SP) were examined in prepubertal rats. A sex difference in AP-SP is evident by age 50 days [males, 287 +/- 35 fmol/mg protein (mean +/- SE); females, 103 +/- 17; P less than 0.05], and this difference becomes greater by 75 days (males, 543 +/- 54; females, 146 +/- 11.5; P less than 0.01). Hypothyroidism was induced in male and female pups by giving lactating dams 0.1% methimazole (wt/vol) in their drinking water after parturition. There was a marked and significant increase in AP-SP in 21-day-old hypothyroid compared to euthyroid control pups. Male pups were made thyrotoxic by daily treatment with T4 (10 micrograms/rat, sc) from age 8 to 15 days. AP-SP was 4 times lower in the thyrotoxic than in the euthyroid pups (P less than 0.001). Rats ovariectomized at age 22 days and killed on day 35 revealed no change in AP-SP, in contrast to the rise in AP-SP in the ovariectomized adult rat. Female pups were treated with dihydrotestosterone (DHT; 50 micrograms/day) or testosterone (50 micrograms/day) from age 8-20 days. Neither androgen induced a change in AP-SP. Female pups which received estradiol (E2; 0.5 micrograms/day) or testosterone (75 micrograms/day) from age 8-20 days also had no change in AP-SP. As opposed to the lack of effect of E2 and DHT on AP-SP in female rats younger than 22 days, E2 (1 microgram/100 g BW daily) caused a decrease and DHT (100 micrograms/100 g BW daily) caused an increase in AP-SP in female rats treated from 22-35 days of age [E2, 91 +/- 6.9; DHT, 226 +/- 31 (P less than 0.05 vs. control for both); control, 154 +/- 13]. We conclude that the responsiveness of AP-SP to alterations in thyroid status is present at the youngest age studied. In contrast, the responsiveness of AP-SP to changes in the levels of gonadal steroids is absent in the infantile period and requires a maturational process that becomes evident during the juvenile state of sexual development.     

Prolactin modulates the gonadotropin response to the negative feedback effect of testosterone in immature male rats

The effects of hyperprolactinemia (hyperPRL) and hypoprolactinemia (hypoPRL) on pituitary gonadotropin secretion and the feedback sensitivity to testosterone (T) were evaluated in immature male rats. At 34 days of age, rats were divided into three groups: group 1, controls, injected with oil; group 2, treated with bromocriptine mesylate (CB-154; 250 micrograms in oil/rat X day); and group 3, subjected to the transplantation of one pituitary from an adult female rat under the kidney capsule and treated with oil. The treatments were continued for 14 days. On day 8, each of these groups were further divided into three subgroups: intact, castrated, and castrated plus T treated. T treatment consisted of injection of T propionate (TP; 50 micrograms in oil/rat) on alternate days starting immediately after castration. Blood samples were obtained by cardiac puncture throughout the study. Plasma PRL levels were significantly reduced by CB-154 treatment and significantly increased by the pituitary graft (P less than 0.001). In intact immature male rats, hyper- or hypoPRL did not affect plasma LH levels, whereas hyperPRL reduced (P less than 0.01) plasma FSH concentrations. The postcastration increase in circulating LH levels was significantly increased (P less than 0.001) in rats treated with CB-154 24 h after castration. Moreover, the suppressive effects of TP on plasma LH and FSH levels were significantly (P less than 0.05) attenuated in hypoPRL rats. In pituitary-grafted rats, effects of castration and TP replacement on plasma LH levels did not differ from those in control rats. These results demonstrate that subnormal levels of PRL reduce the sensitivity of the hypothalamic-pituitary system to feedback inhibition by T. In contrast to previous findings in the adult rats, acute hyperPRL in immature male rats did not affect the negative feedback action of T on gonadotropin secretion.     

Progesterone and the control of functional luteolysis, of secretion of prolactin and of pituitary LHRH responsiveness. A study with pseudopregnant rats kept in alternating and constant lighting conditions

The effect of exogenous progesterone (P) on the corpus luteum function (in terms of the secretion of P and 20-alpha-dihydroprogesterone (DHP), on the secretion of prolactin (Prl) and on the pituitary responsiveness to LHRH was studied in pseudopregnant (PSP) rats kept in alternating and constant lighting conditions (LD-PSP and LL-PSP rats, respectively). Rats were rendered pseudopregnant by appropriately timed stimulation of the cervix uteri (LL rats first received an ovulatory dose of hCG). LH responses were induced by constant rate infusion of LHRH (104 ng/h for 21 h). P was delivered by subcutaneously inserted Silastic implants; control rats received sham implants. In both LD-and LL-PSP rats the plasma P and DHP levels were high on day 8 of PSP. On day 12, however, the plasma P levels had fallen but the DHP levels had risen, demonstrating that between days 8 and 12 functional luteolysis had occurred and that neither the production of P and DHP, nor the timing of luteolysis are under the control of the lighting conditions. On day 12 of PSP the pituitary responsiveness to LHRH was much higher than on day 8. Moreover, on days 8/9 of PSP peaks of Prl were seen in all rats, but on days 11/12 such peaks were largely absent. In LD-PSP rats 'nocturnal' Prl peaks were seen on days 8/9 in all 9 experimental animals, but 'diurnal' peaks were seen in only 4 of these animals. Also, the diurnal peaks were on average much lower than the nocturnal peaks.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increase in ovarian 15-hydroxyeicosatetraenoic acid during ovulation in the gonadotropin-primed immature rat

The ovarian level of 15-hydroxyeicosatetraenoic acid (15-HETE) was measured by RIA during ovulation in gonadotropin-primed immature Wistar rats. The ovulatory process was initiated in 25-day-old rats by a 10-IU injection of hCG sc 2 days after the animals had been primed with 10 IU PMSG, sc. Ovarian follicles begin to ovulate 10 h after hCG. At 0 h after hCG, the ovarian 15-HETE level was 0.6 +/- 0.2 ng/mg ovarian protein. At 6 h the 15-HETE level increased sharply to 27.3 +/- 4.2 ng/mg protein and reached a peak of 50.0 +/- 9.8 ng/mg protein at 10 h. Ovarian 15-HETE decreased significantly between 10-16 h after hCG (when ovulation was essentially completed). The pattern of secretion of this 15-lipoxygenase product was reciprocal to the pattern of secretion of leukotriene-B4 by the rat ovary. Ovarian 15-HETE production and ovulation were inhibited in a dose-dependent manner when indomethacin was administered sc 1 h after hCG in doses ranging from 0.10-10.0 mg/rat. In contrast, the synthesis of ovarian prostaglandins-E and -F was inhibited by a dose of indomethacin as low as 0.0316 mg/rat, but this dose did not significantly affect the ovarian 15-HETE level or the ovulation rate. Therefore, the ovulation rate was more closely correlated with the ovarian 15-HETE level (P less than 0.001) than with the ovarian levels of either prostaglandin-E or -F (0.10 greater than P greater than 0.05). The results suggest that products of the 15-lipoxygenase pathway of arachidonic acid metabolism may be important in the biochemical events of mammalian ovulation.     

Effect of hysterectomy on serum luteinizing hormone concentrations and on corpus luteum function in the rat.

Serum progesterone, follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were estimated in intact and hysterectomized pseudopregnant rats. Progesterone concentrations increased significantly from day 2 of pseudopregnancy (PSP) onwards, and a plateau was reached on days 4 and 5. No significant differences in progesterone concentrations between intact and long-term hysterectomized animals were observed until day 10 of PSP. In the intact rats, progesterone concentrations decreased after day 8, but in the hysterectomized rats they remained elevated until days 18-20 of PSP. No differences between FSH concentrations in intact and hysterectomized rats were found. In hysterectomized rats, however, LH concentrations were significantly lower than those in the intact rats on days 2-7 of PSP. When hysterectomy was performed on day 2 of PSP (acute hysterectomy) lower LH concentrations were also found in the hysterectomized animals compared with sham-operated animals. No differences in progesterone concentrations were found between sham-operated controls and acutely hysterectomized animals on days 3-8 of PSP. It was found that LH concentrations in ovariectomized long-term hysterectomized rats were lower than those in ovariectomized, but otherwise intact, animals. In contrast to its effect on tonic LH secretion, long-term hysterectomy had no influence on the surge of LH during the afternoon of proestrus. In both intact and long-term hysterectomized rats the duration of PSP was not significantly altered after transplantation of an ovary under the kidney capsule and the removal of the ovaries in situ. It is concluded that hysterectomy leads to a decreased LH secretion by the pituitary gland, but has no influence on the maximal progesterone concentrations during PSP. The significance of these findings, particularly with regard to the prolongation of PSP after hysterectomy, is discussed.     

Effects of the uterus and the ovaries on growth, somatotropin and somatomedin A in developing rats

The effects of hysterectomy and ovariectomy on plasma concentrations of GH, somatomedin A, TSH and thyroxine (T4) were studied in developing rats. Four groups of 24-day-old rats were ovariectomized, ovohysterectomized, hysterectomized or sham-operated. Their weights, lengths and plasma hormone concentrations were measured at 26, 43, 64, 78 and 92 days of age to investigate pre- and postpubertal differences caused by the uterus or ovaries. Plasma concentrations of the hormones examined showed a successive rise with time, but GH and somatomedin A concentrations rose mainly after the opening of the vagina (days 50-55). Higher GH and somatomedin A concentrations were found in the plasma of ovariectomized animals than in ovohysterectomized controls before puberty (GH: 260-300%, P less than 0.01; somatomedin A: 25-30%, P less than 0.05). Ovariectomized animals weighed more than ovohysterectomized females after puberty (4.5-6%, P less than 0.01). This indicated that the uterus exerted a stimulatory effect on GH-somatomedin A regulation and body weight gain in the absence of the ovaries. Significantly lower plasma somatomedin A (but not GH) concentrations were found in hysterectomized and sham-operated animals than in their respective controls after puberty (30-39%, P less than 0.01) and their final body weight was lower (22-26%, P less than 0.001). There were no consecutive uterus- or ovary-related changes in plasma TSH and T4 levels. It was concluded that both the uterus and ovaries had significant as well as opposite effects on somatomedin A and body weight with the effects of the ovaries being greater than those of the uterus.     

The pattern of ovarian inhibin, estradiol, and androstenedione secretion during the estrous cycle of the ewe

An experiment was conducted in order to determine the pattern of, and the relationships between, the secretion of inhibin, estradiol, and androstenedione by the ovary and the concentration of LH, FSH, and PRL during the estrous cycle of sheep. The estrous cycles of 6 Finn-Merino ewes in which the left ovary had been autotransplanted to the neck were synchronized by two injections of cloprostenol (100 micrograms im) a potent analog of prostaglandin F2 alpha (PG) given 14 days apart. The ewes had ovarian and jugular venous blood samples taken at four hourly intervals from 42 h before the second PG injection until day 6 of the following cycle. All animals responded to PG with the preovulatory LH surge occurring within 58 +/- 2 h (mean +/- SEM). The concentration of FSH in jugular venous plasma fell (P less than 0.001) after the induction of luteolysis and then exhibited 3 peaks, the first coincident with the LH surge, the second on day 1, and the third on day 6. After injection of PG the secretion rates of inhibin, estradiol, and androstenedione increased (P less than 0.05) within 4-8 h. After this increase in the early follicular phase the secretion rate of estradiol continued to rise until the time of the LH surge (P less than 0.001). Although the secretion of androstenedione and inhibin increased in the 36 h before the LH surge the magnitude of this rise was less marked than for estradiol and was not statistically significant. Within 4-8 h of the start of the LH surge the secretion of estradiol and androstenedione declined rapidly reaching barely detectable levels within 16 h (P less than 0.001). In contrast the secretion of inhibin increased after the LH surge reaching a broad peak (P less than 0.05) of approximately 16-h duration, coincident with the second peak of FSH. From days 2-6 mean secretion of inhibin remained relatively stable at 2-6 ng/min although considerable variation was observed in individual profiles. The rate of estradiol secretion increased steadily from its nadir on day 1 to a broad peak centered around day 3 (3-6 ng/min, P less than 0.001) followed by a decline until by day 6 the estradiol secretion rate was less than 1 ng/min (P less than 0.01). The secretory profile for PRL showed a close relationship with estradiol secretion.(ABSTRACT TRUNCATED AT 400 WORDS)