Pituitary Luteinizing Hormone Content Research Articles

The influence of nutrition on reproduction in the ewe 1. Effects on ovulation rate, follicle development and luteinizing hormone release

ABSTRACTTwo groups of 15 ewes in store body condition were either given a maintenance level of feeding or a twice-maintenance level (flushed) during the course of one oestrous cycle. Five ewes from each feeding level were slaughtered at 0, 18 or 48 h after the onset of the oestrus at the end of the treatment period and measurements were made of the luteinizing hormone content of their pituitary, the luteinizing hormone concentration in their blood plasma, their ovulation rates, and ovarian follicle numbers and sizes.‘Flushed’ ewes had a significantly higher ovulation rate (260, s.e. 0·24 v. 1·80, s.e. 0·20; P <0·05), although there was no significant difference in either pituitary luteinizing hormone content or plasma luteinizing hormone concentrations at oestrus.Analysis of the patterns of ovarian follicle distribution suggest that flushing ewes for one oestrous cycle might increase ovulation rate by preventing the late atresia of large follicles in the last 30 h before ovulation.

Regarding the validity of the endpoint response of the mouse (McKenzie) bioassay for thyrotrophin (TSH).

Abstract. The release of radiolabelled thyroid hormone into the circulation in low iodine fed mice has been used extensively as a bioassay for thyroid stimulating hormone (TSH). However, the specificity of several bioassays of pituitary hormones have been subject to question. Consequently, the validity of the assay endpoint for TSH in the mouse was re-evaluated with respect to the effect of luteinizing hormone (LH) whose chemical composition closely resembles that of TSH. Mice, prepared for bioassay of TSH received injections of purified LH or α or β subunits of LH. Identical doses of LH and LH subunits were quantified by LH and TSH radioimmunoassays and the results compared with those obtained by the bioassay. Microgram quantities of LH and subunits of LH elicited appreciable responses in the TSH bioassay but produced only negligible effects in the TSH radioimmunoassay. The response of the TSH bioassay of LH and α or β subunits of LH was 40–56% that obtained with LH radioimmunoassay. However, the pituitary concentrations obtained by TSH bioassay when compared with those obtained by radioimmunoassays for TSH, LH, or growth hormone (GH) paralleled closely the TSH radioimmunoassay data, although in terms of quantitative estimates, there was a 15-fold discrepancy between the TSH assays. Estimations of pituitary concentrations of LH lead to the conclusion that, at the doses normally employed, most crude rat pituitary extracts do not contain sufficient quantities of LH to alter significantly bioassayable (McKenzie) estimates of TSH.

A change in basal FSH release accompanies the onset of the second or selective phase of increased serum FSH in the cyclic rat

Experiments were undertaken to investigate if changes occur at the level of the anterior pituitary gland to result in selective follicle-stimulating hormone (FSH) release during late proestrus in the cyclic rat. At 1200 h proestrus, prior to the preovulatory luteinizing hormone (LH) surge in serum and the accompanying first phase of FSH release, serum LH and FSH concentrations were low. At 2400 h proestrus, after the LH surge and shortly after the onset of the second or selective phase of FSH release, serum LH was low, serum FSH was elevated about 4-fold, pituitary LH concentration was decreased about one-half and pituitary FSH concentration was not significantly decreased. During a two hour in vitro incubation, pituitaries collected at 2400 h released nearly two-thirds less LH and 2.5 times more FSH than did pituitaries collected at 1200 h. Addition of luteinizing hormone releasing hormone (LHRH) to the incubations caused increased pituitary LH and FSH release. However, the LH and FSH increments due to LHRH in the 2400 h pituitaries were not different from those in the 1200 h pituitaries. The results indicate that a change occurs in the rat anterior pituitary gland during the period of the LH surge and first phase of FSH release which results in a selective increase in the basal FSH secretory rate. It is suggested that this change is primarily responsible for the selective increase in serum FSH which occurs during the second phase of FSH release.

Influence of subcutaneous deposits of melatonin on the antigonadotrophic effects of blinding and anosmia in male rats. A dose-response study.

23-day-old male rats were left intact, rendered blind and anosmic, pinealectomized together with blinding and anosmia, or subcutaneously implanted with graded doses of melatonin in beeswax immediately following surgical blinding and anosmia. 5 weeks later, blind, anosmic animals were found to have significantly depressed anterior pituitary, testicular, and accessory sex organ weights. Both pituitary and plasma prolactin and luteinizing hormone (LH) concentrations were also significantly suppressed. Pinealectomy of blind, anosmic animals completely restored testicular and accessory organ weights. Likewise, pituitary LH and prolactin and plasma LH levels were also restored to intact control levels by pineal removal. Only the highest dose of melatonin (1 mg) restored the testicular and accessory sex organ weights to those of the intact controls. As little as 1 microgram melatonin restored plasma and pituitary LH concentrations to the levels of the intact controls. However, none of the dosages of melatonin reversed plasma prolactin concentrations to those of the untreated animals. The decrease in pituitary prolactin induced by blinding and anosmia was reversed by pinealectomy or by the lower doses (1, 50 or 100 micrograms) of melatonin. These results indicate that melatonin can reverse the antigonadotrophic effects of blinding and anosmia in male rats. The minimal dose of melatonin required to restore testicular and accessory sex organ weights in blind, anosmic rats is 1 mg implanted subcutaneously in beeswax.

Interactions of gonadal steroids, gonadotropins and gonadotropin-releasing hormones in sexual maturation

Plasma and pituitary concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in individual male rats pretreated with testosterone and its 5α-reduced metabolites for various lengths of time at various stages of sexual maturation. The degree of androgen induced inhibition of the gonadotropins depended on the maturation of the animals and the administration of synthetic LH-RH could not restore the levels to the pre-androgenblocked periods. The stimulation of LH and FSH due to LH-RH was also dependent on age and time-interval between the treatment with androgen and the collection of samples. The chronic treatment of dihydrotestosterone (DHT) and 3α, 5α-androstanediol (ADIOL) daily from day 1 after birth to day 90 demonstrated extremely variable results. Although release and synthesis of LH was inhibited due to LH, FSH was inhibited only between ages 25 and 40 days. From day 50 onwards FSH in the DHT-treated animals registered higher values. With ADIOL, although LH showed mild inhibitory effects at certain age points, FSH demonstrated stimulating values. Pituitary contents of both LH and FSH were markedly higher in the ADIOL-treated animals than the levels seen in the control group. This significant augmentation of serum and pituitary FSH as well as pituitary LH contents in the pubertal and adult animals with chronic treatment of ADIOL suggests that this metabolite may have an action not shared by the parent compound.

Pituitary Gonadotropin Inhibition by a Highly Active Analog of Luteinizing Hormone-Releasing Hormone

Chronic treatment with highly active analogs of luteinizing hormone (LH)-releasing hormone (LH-RH) induces "paradoxical" antifertility effects. Intact male rats, a reduction in testosterone production is observed after the administration of [D-Ser(But)6]-LH-RH(1-9)ethylamide (burserelin, Hoe 766), 50 ng/day subcutaneously for 4 weeks. In castrated male rats treated with the same dose of analog, plasma LH levels were reduced from days 14 to 28 and plasma follicle-stimulating hormone (FSH) levels were reduced from days 21 to 28 of treatment. Pituitary LH and FSH concentrations were also decreased. The plasma prolactin level was reduced at 14 days of treatment. The hypothalamic LH-RH content remained unchanged and the adrenal corticosterone content was lowered. These findings indicate a direct inhibitory effect of the analog on gonadotropin secretion in the absence of the gonads, and may explain some paradoxical antifertility effects observed with high doses of LH-RH analogs which exceed the physiologic dose range.

Effect of oral contraceptive on the pituitary and plasma L.H. levels and on the hypothalamic LH-RH level (author's transl)

The effects of the oral contraceptive on the pituitary content and plasma level of LH and the hypothalamic LH-RH level were investigated in 16 adult female rabbits. The oral contraceptive preparation, Sophia-C (Norethindrone 2mg + Mestranol 0.1 mg), as administered orally by a stomach tube each day for 7 days in 8 adult female rabbits. At the end of the treatment, the rabbits were bled from the abdominal aorta into heparinized syringes and the plasma was separated. The stalk median eminences were excised. All the materials were stored in -80 degrees C until assayed. Plasma level and the pituitary content of LH and the hypothalamic LH-RH were measured by radioimmunoassay. All the dose response curved were drawn using logitlog transformation. Radioimmunoassay procedures for LH was described in detail elsewhere. Purified rabbit LH for iodination (125-I) and strandard were prepared by T. Makino and R.O. Greep, at Research Laboratories for Human Reproduction, Harvard Medical School, Boston, U.S.A. The starting B/T was 25% at the final dilution of the antibody of 1/20,000. Minimal detectable quantity was about 40 pg/tube. The 50% intercepts were approximately 460 pg/tube. Radioimmunoassay procedures for LH-RH were performed according to the method described by Arimura et al. Antiserum against synthetic LH-RH was kindly supplied to us by Drs. A. Arimura and A.V. Schally, New Orleans, U'S.A. The synthetic LH-RH was kindly supplied to us by Dr. N. Yanaihara. The starting B/T ratio was 29% at the final dilution of the antibody of I/17,500. Minimal detectable quantity was about 40pg/tube and the 50% intercepts were 150pg/tube. It has been assumed that oral contraceptive drugs exert their action by blocking the hypothalamic LH-RH, resulting in a depression of the plasma level of LH, because plasma level of LH returned to the normal level when LH-RH was administered intravenously even while oral contraceptive steroids were given continuously. However, these findings concerning the site of action of the drugs furnished only indirect evidences. The possibility of a direct inhibitary effect of these steroids on the anterior pituitary cannot be ruled out. Administration of 2mg of Norethindrone and 0.1mg of Mestranol significantly depressed both the pituitary content and the plasma level of LH. On the other hand, they significantly increased the hypothalamic LH-RH level. Those findings strongly suggested the direct action of this drug on the anterior pituitary in the female adult rabbits. Detailed mechanisms on how the hypothalamic LH-RH was increased were not known in this experiment, further investigations are now in progress.

Endocrine effects of chronic administration of psychoactive drugs to prepubertal male rats. II. LSD.

The endocrine effects of chronic D-lysergic acid diethylamide (LSD) administration to prepubertal animals were studied by injecting intraperitoneally three times a week for a month either 100 mug or 500 mug of the psychoactive drug per kilogram or the vehicle to groups of Sprague-Dawley male rats starting at 21 days of age. Animals injected with either dosage of LSD had smaller body weights than controls and tail length was significantly reduced in the high dosage group, plasma levels of growth hormone (GH) were decreased in the high dosage group, and pituitary levels in the low dosage group. Plasma levels and pituitary concentrations of luteinizing hormone and follicle stimulating hormone were not significantly modified by the drug. The low dosage of LSD decreased the brain levels of noradrenaline and increased those of dopamine, while the high dosage decreased those of 5-hydroxyindoleacetic acid. These data suggest that LSD, when administered chronically to developing animals, can inhibit body growth probably by altering the secretion of GH through modifications of its neuroendocrine control.

The interaction of castration and photoperiod in the regulation of hypophyseal and serum gonadotropin levels in male golden hamsters.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in intact and castrate adult male hamsters maintained on photostimulatory (LD 14:10) and non-photostimulatory (LD 6:18) light:dark cycles to assess the interaction of photic stimuli and gonadal hormones on pituitary gonadotropin release. Immunoreactive serum LH and FSH levels increased 1.6- and 8-fold respectively, within 3 days after photostimulated hamsters were castrated. In contrast, castration failed to alter serum LH concentration and had only a slight, if any, effect on FSH concentration in hamsters exposed to nonstimulatory photoperiods that induced testicular atrophy. In a second experiment, male hamsters previously maintained on LD 14:10 were castrated, transferred with intact animals to LD 6:18, and killed periodically over 60 days. In intact animals, pituitary content and serum levels of LH and FSH declined substantially during exposure to the non-stimulatory LD 6:18 cycle. In castrated animals, serum LH and FSH levels which had increased 2- and 8-fold in response to the castration eventually declined to about the levels found in the intact initial control animals. In contrast to serum gonadotropins, the increased hypophyseal content of LH and FSH following castration was not reduced during exposure to LD 6:18. Exposure to nonstimulatory photoperiods does not alter the increased hypophyseal LH and FSH content observed after castration. However, our results indicate that exposure to short days renders the hypothalamic-hypophyseal neuroendocrine system governing gonadotropin release relatively insensitive to gonadal steroid hormone feedback.

Effects of x-ray irradiation on the subsequent gonadotropin secretion in normal and neonatally estrogenized female rats.

Female rats were irradiated with 190R of X-rays at 10 days of age and sacrificed 4, 7 or 12 months later. Their ovaries were histologically examined and serum levels and pituitary contents of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay. Both serum levels and pituitary contents of LH and FSH rose significantly 4 and 7 months after irradiation, although the ovaries were markedly reduced in weight. On the contrary, 12 months after irradiation, the ovaries increased in weight and consisted mostly of polyhedral, hyperplastic interstitial cell masses, and both LH and FSH in the serum and pituitary were reduced to normal levels. These characteristic changes in the ovarian weight and histological appearance could not be observed in the similarly irradiated animals which were received daily injections of estrone for the first 30 days of postnatal life, i.e., daily injections of 50 mug for the first 10 days, 100 mug for the middle 10 days and 200 mug for the last 10 days. Serum LH levels of the estrogenized irradiated rats at 7 or 12 months of age did not elevate although those of FSH were significantly higher than the non-irradiated intact levels. From these results, a rise in the blood levels of LH and the FSH may be attributed to the increase in weight and the histological changes in the ovaries of the irradiated female rats, and the elevation of only FSh level may not result in the abnormal growth of the irradiated ovaries.

The effect of ovarian steroid feedback upon radioimmunoreactive luteinizing hormone releasing hormone in the hypothalamus.

A radioimmunoassay (RIA) method for luteinizing hormone (LH) releasing hormone (RH) utilizing rabbit antiserum against synthetic (Glu1)-LH-RH coupled with human serum albumin at the N-terminus, is described. This assay system for LH-RH also cross-reacted with several LH-RH analogues or fragments, but not with pituitary trophic hormones. The assay was performed on the hypothalamic extracts of adult ovariectomized rats and female immature rats which had been treated with estradiol. The FSH and LH levels in the pituitary gland and serum of the same animals were determined by RIA. The radioimmunoreactive LH-RH content of the stalk median eminence markedly increased seven days after ovariectomy. The serum levels and the pituitary contents of FSH and LH of the same rats were also significantly augmented. In immature rats, the hypothalamic content of LH-RH, as measured by RIA, was significantly increased one hour after the injection of estradiol. The FSH and LH levels in the pituitary showed a significant rise after 7 hours.

Factors Influencing Pituitary Glycogen Metabolism and Gonadotropic Hormone Release. I. Luteinizing Hormone-Releasing Hormone

The way in which luteinizing hormone (LH) and follicle stimulating h ormone (FSH) are related to pituitary glycogen metabolism is investigated by measuring pituitary glycogen content and the activity of glycogen synthetase and glycogen phosphorylase in LH-releasing hormone (LH-RH) treated rat pituitaries. The presence of LH-RH (15 ng/flask) resulted in a significant (p less than .05) release of LH and FSH after 4 hours of incubation. Pituitary LH content was also raised (p less than .05). 3 ng of LH-RH increased pituitary cyclic adenosine monophosphate (AMP) content by 475% in 10 minutes of incubation. Glycogen phosphorylase was converted to its active form with 1-10 ng LH-RH per flask; this glycogenolytic activity occurred within 5 minutes (p less than .01) and was also induced by cyclic AMP in the presence of theophylline. The forms of glycogen synthetase did not appear to be affected by LH-RH or cyclic AMP. It is concluded that pituitary glycogen may be an energy source for release of gonadotropins via LH-RH.

Pituitary responsiveness to luteinizing hormone-releasing factor in normal and androgenized female rats.

In order to compare directly the functional responsiveness of the pituitary gland in the androgenized rat with that of the normal female, luteinizing hormone-releasing factor (LRF) was administered intravenously and plasma and pituitary luteinizing hormone (LH) was measured utilizing a radioimmunoassay. Just prior to the critical period proestrous normal adult females received an ovulation blocking dose of pentobarbital; androgenized rats were similarly treated. Blood was collected by jugular puncture and then 0.1, 1.0, 10, 100 or 500 ng LRF/100 g body wt was administered. The rats were bled 15 minutes later and decapitated after 45 minutes at which time trunk blood and anterior pituitary glands were collected. Pituitary response to LRF as measured by plasma LH was identical in both groups of rats except at the 500 ng dose. Pituitary LH concentration was significantly reduced only in the androgenized rats given the 500 ng dose of LRF. Ovarian sensitivity to LH was also measured by studying the ovulatory r...

Plasma and pituitary luteinizing hormone in intact and castrated tree sparrows ( Spizella arborea) during a photoinduced gonadal cycle

Plasma and pituitary levels of immunoreactive luteinizing hormone (LH) were measured in female, male, and castrated male tree sparrows during a photoinduced gonadal cycle. Our aims were to compare patterns of LH secretion, particularly during spontaneous gonadal regression, and to determine the testes' influence on the secretory pattern of males. Seven days after females were transferred from 8- to 20-hr daily photoperiods, the concentration of plasma LH had increased 11-fold. Two weeks later, it had declined to a level only 3-fold greater than that in short-day controls, where it remained until day 56, when ovarian growth culminated. The onset of ovarian regression between days 56 and 77 was accompanied by a reduction in plasma LH to the prestimulation level (ca. 0.5 ng/ml) and by a similar reduction in pituitary LH content, which, by contrast, had increased steadily through day 28. The plasma cycle of males was quantitatively similar, but it reflected the transition from photosensitivity to photorefractoriness less incisively. Pituitary cycles of males and females were qualitatively similar. The concentration of plasma LH in castrates, compared with that in intact males, was elevated through day 56. A 4-fold increase in pituitary LH preceded a reduction in the circulating level that paralleled the onset of testicular and ovarian regression. Qualitative similarity among plasma cycles plus the eventual reduction of plasma LH in castrates to the low level characteristic of chronically photostimulated birds of both sexes argues that the LH-release mechanism becomes refractory in castrates as in males and females. We, therefore, conclude that testicular steroids are not obligatory determinants of the temporal pattern of circulating LH in photostimulated males, yet they apparently inhibit the photoresponsive hypothalamohypophysial axis. An elevated plasma level in short-day castrates suggests that a functional relationship between the hypothalamohypophysial axis and the testes exists also in nonphotostimulated males.

Prolactin and luteinizing hormone cells of pregnant and lactating rats as studied by immunohistochemistry and radioimmunoassay.

AbstractThe objective was to describe the cytological changes that occur in prolactin and luteinizing hormone (LH) cells of the rat hypophysis during pregnancy and lactation and to correlate these changes with secretory activity of the two cell types. The cells were demonstrated with immunohistochemistry and secretory activity was indicated by pituitary and serum hormone concentrations as measured by radioimmunoassay.During pregnancy, two forms of prolactin cells were observed in the pars distalis. One form (prolactin cell I) was small, polyhedral, and constituted most of the prolactin cell population. A second form (prolactin cell II) was found occasionally in pituitary glands of nonpregnant rats and became prominent during pregnancy. It was polyhedral, many times larger than prolactin cell I, and had a restricted distribution in the pars distalis. During gestation prolactin cells I exhibited little change in size, number and staining capacity. Similarly, pituitary and serum prolactin concentrations indicated that the hypophysis releases little prolactin during pregnancy, except for the first few days after conception and before parturition. During lactation, the staining intensity of prolactin cells I and the pituitary prolactin concentration varied little. Prolactin cells II were lightly stained and rare throughout lactation.The staining capacity of luteinizing hormone (LH‐) cells increased as pregnancy progressed in parallel with a rising pituitary concentration of LH during the first half of pregnancy. However, the immunohistochemical procedure appeared to be too insensitive to reflect the gradual fall in pituitary LH concentration during late pregnancy. During early lactation, the reduced staining capacity of LH‐cells was correlated with a low pituitary concentration.

Serum and pituitary luteinizing hormone, follicle-stimulating hormone and prolactin levels in gonadectomized male, female and androgenized female rats treated with oestradiol benzoate.

SUMMARY Changes in serum concentrations and pituitary content of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin, determined by radioimmunoassay, were studied after oestradiol benzoate (OEB) administration to gonadectomized male and female rats and to gonadectomized females androgenized with 50 μg testosterone propionate on the 5th day post-partum. Oestradiol benzoate (0·05–50 μg) was given once a day for 7 days beginning 3 weeks after removal of the gonads. A rise in serum LH concentration was produced by 0·05 μg OEB in all animals, but a reduction was found with the larger doses. Serum FSH increased in females injected with 0·05 μg OEB, but males and androgenized females had decreased FSH levels with all doses. The prolactin concentrations increased in the sera of all animals treated with 0·05 μg or 0·5 μg oestrogen. Males showed no further increases with larger doses. A very large increase was found in females given 5 μg but 50 μg did not have this stimulatory effect. Dose-dependent increases in serum prolactin were noted in androgenized females. Pituitary prolactin content increased in females and androgenized females treated with oestrogen; a slight, but significant, increase was found only in the males given 50 μg. Pituitary LH was increased only in the animals receiving a large amount of oestrogen (5 or 50 μg). Glandular FSH increased in the males and androgenized females given 0·5 μg OEB, but in all animals a reduction in this gonadotrophin was found after giving 50 μg of the oestrogen. The results indicate that androgenization alters the normal female hypothalamo-hypophysial response to oestrogen but it does not induce the response pattern of the male.

Effect of starvation on gonadotropin secretion in intact and castrated male rats.

The effect of starvation on serum and pituitary concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was studied in intact and in castrated 4-month-old male rats. In intact rats, starvation for 7 days resulted in lower serum FSH (P < 0.05) and LH (P < 0.01) levels than in fed controls. Body, pituitary, and ventral prostate weights were also lower (P < 0.01) in rats starved for 7 days than in controls. The starvation-induced reductions in the serum levels of FSH and LH occurred within 48 and 24 h, respectively, after food was withheld. Rats subjected to starvation for 7 days immediately following castration showed higher (P < 0.05) pituitary concentrations of both FSH and LH than fed castrates. The serum levels of FSH and LH were equally high in both groups of castrates.The results suggest that starvation results in a rapid inhibition of gonadotropin secretion and the inhibition is dependent on an intact negative-feedback system.

Changes in FSH, LH and prolactin secretion during estrous cycle in rats.

Serum and pituitary follicle-stimulating hormone (FSH) luteinizing hormone (LH) and prolactin contents during the normal rat estrous cycles were assayed every 2 hours in adult female rats of Holtzman strain (lights on 5 a.m. to 7 p.m.). NIAMD rat FSH LH and prolactin radioimmunoassay kits were used. Previously bioassay methods were used but they were not satisfactory in assaying the blood FSH and LH levels because of their low sensitivity. The serum LH surge was observed from 6 p.m. to 7 p.m. on the proestrus day. The serum FSH surge was observed from 7 p.m. on the proestrous day to 5 p.m. on the estrous day. The serum prolactin concentrations began to rise at 1 p.m. on the proestrous day and remained at high levels until 10 a.m. on the estrous day. The reduction in pituitary FSH LH and prolactin content was simultaneously observed from 7 p.m. to 11 p.m. on the proestrous day. These results confirm the data reported by Daane and Parlow (1971). They also demonstrate no diurnal rhythm on the first and second diestrous day as reported by Gay et al (1970).

The role of Pineal Principles in Ovulation

This chapter attempts to answer the questions, which seem to be fundamental in the consideration of the role of the pineal gland in the control of ovulation. An anovulatory syndrome with permanent vaginal cornification and polyfollicular ovaries was provoked by frontal deafferentation of the hypothalamus. Pinealectomy, as well as bilateral removal of the superior sympathetic cervical ganglia, elicited ovulation and formation of corpora lutea in these anovulatory rats. The effect of pinealectomy and of ganglionectomy was counteracted by chronic administration of serotonin. In 1968, Fraschini and Martini report that pinealectomy increases the synthesis and mobilization of luteinizing hormone (LH) in the adult male rat. In addition, implantation of a pineal gland or of purified melatonin into the median eminence of the hypothalamus, or into the reticular formation of the mesencephalon, caused a significant decrease in the elevated pituitary LH content of castrated male rats. These results furnished evidence supporting the hypothesis that the pineal body has an inhibitory effect on LH secretion by the anterior pituitary.

Luteinizing hormone, prolactin and ovarian 20 -hydroxysteroid dehydrogenase levels during pregnancy and pseudopregnancy in the rat.

Ovarian α—hydroxysteroid dehydrogenase (α—OH—SDH) activity and serum and pituitary concentrations of luteinizing hormone (LH) and prolactin were determined in individual rats at selected times during the estrous cycle, normal pseudopregnancy, prolonged pseudopregnancy due to hysterectomy or induced deciduomata, and pregnancy. During die 5-day cycle, α—OHSDH activity was lowest at diestrus II (38.8 ± 2.5 mU enzyme/mg protein), increased 2-fold at proestrus, then declined at estrus (52.8 ± 4.8). Except for sharp peaks at proestrus, serum LH and prolactin levels were consistently low at diestrus and estrus (mean ± SE over 3 days of diestrus = 15.5 ± 1.4 ng LH/ml serum and 48.1 ± 3.1 ng prolactin/ml serum). During normal pseudopregnancy, enzyme activity on Day 1 was comparable to that found at diestrus II of the cycle, then declined 3-fold at Day 6. After Day 6, α— OH—SDH increased steadily until Day 13 (60.9 ± 4.6 mU/mg protein). From Days 1-6, enzyme levels in pregnant rats were quite similar to those in no...