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PubMed1987

Superovulation in the cow using estradiol 17beta or GnRH in conjunction with FSH-P.

A study was designed to evaluate the superovulatory response in the cow when either estradiol 17beta or gonadotrophin releasing hormone (GnRH) was used in a superovulatory regimen with follicle stimulating hormone (FSH-P). Fifty-four cyclic crossbred females were superovulated in replicates between Days 8 and 12 of their cycle. All animals were treated with 28 mg of FSH-P in twice-daily decreasing doses, each receiving 500 mug cloprostenol (PGF) 48 h after initiation of treatment. Group 1 served as FSH-P controls, Group 2 received FSH-P and 400 mug of estradiol 17beta 36 h after PGF, and Group 3 received FSH-P and 250 mug GnRH 48 h after PGF. Inseminations with one vial of frozen semen were done at 12, 24 and 36 h after the onset of estrus. Ova/embryos were collected nonsurgically at Day 7 postestrus. Numbers of corpora lutea (CL) were recorded after palpation per rectum and the recovered ova and embryos were evaluated. All females were bled for endocrine examination. There were no differences in ovarian response among these treatments. Mean total ova/embryos collected in Group 3 was significantly higher than in Groups 1 or 2 (P < 0.05); however, no significant difference existed between groups in the mean numbers of fertilized or transferable embryos. Similarly, no significant differences existed between groups for recovery rate, fertilization rate, or percentage of transferable embryos. Serum estradiol levels were significantly higher at the expected end of ovulation in Group 2, and this tended to be associated with higher fertilization and transferable embryo rates. Furthermore, a significant positive correlation was found to exist between CL numbers and each of the ova/embryo parameters and the estradiol levels at estrus.

Journal Article↗
PubMed1990

Superovulation in heifers given FSH initiated either at day 2 or day 10 of the estrous cycle.

The aim of this study was to determine if initiation of superovulation in heifers during the time of development of the first dominant follicle (Days 2 to 6) would give equivalent ovulation and embryo production rates as treatment initiated at mid-cycle. Estrus was synchronized in 60 beef heifers using luprostiol (PG) and they were randomly allocated to treatment with 4.5, 3.5, 2.5 and 1.5 mg of porcine follicle stimulating hormone (FSH) administered twice daily, either on Days 2, 4, 5 and 6 (Day-2 group), respectively, or with similar doses at four consecutive days during mid-cycle (Day-10 group, initiation on Day 9 to 11). All heifers received 500 mug cloprostenol at the fifth FSH injection and 250 mug at the sixth injection. Blood samples for progesterone determination were collected at the time of FSH injections. Heifers were slaughtered 7 d post estrus, and the number of ovulations and large follicles (>/=10mm) were determined on visual inspection of the ovary. Following flushing of the uterine horns the quality of embryos and the fertilization rate were determined. Significant differences between treatments were determined using a two-sided t-test, and frequency distributions were compared using Chi-square tests. The mean number (+/-SEM) of ovulations for heifers in the Day-10 group was 12.9+/-1.0, and 8.5+/-0.9 embryos were recovered. Both the number of ovulations (6.7+/-0.8) and embryos recovered (4.1+/-0.6) were lower (P=0.0001) in heifers in the Day-2 group. Following grading based on a morphological basis, a higher number (P=0.002) of embryos was categorized as Grades 1 and 2 (4.1+/-0.6) and Grade 3 (2.1+/-0.4) in Day-10 heifers than in the Day-2 group (Grade 1 and 2, 1.9+/-0.3; Grade 3, 0.7+/-0.2). The number of Grade 4 and 5 embryos (Day 10, 1.6+/-0.2; Day 2, 1.4+/-0.2) and the number of unfertilized ova (Day 10, 0.7+/-0.4; Day 2, 0.2+/-0.1) did not differ between treatments. Progesterone concentrations were lower (P=0.0001) in Day-2 heifers at FSH treatment prior to prostaglandin, and the decline was more rapid following prostaglandin injection at Day 5 (P=0.02). Results of this study indicate that the number of ovulations and embryos recovered was lower in heifers when FSH treatment was initiated on Day 2 compared with Day 10 of the estrous cycle.

Journal Article↗
PubMed1990

LH and FSH response of Holstein heifers to fertirelin acetate, gonadorelin and buserelin.

This study was conducted to describe the changes in serum LH and FSH concentrations in Holstein heifers following intramuscular (i.m.) injection of various dosages of fertirelin acetate and other commercially available GnRH products at their labeled dosages. The design was an incomplete Latin-square which gave nine replicates of each treatment. Treatments administered on Days 8 to 16 of the estrous cycle consisted of saline; 25, 50, 100 or 200 microg fertirelin acetate; 100, 250 or 500 microg gonadorelin; and 10 or 20 microg buserelin. Blood samples were collected via jugular catheters from 1 h before to 8 h after each injection. Log (Base 2) area under the LH and FSH curves (log AUC) were used to evaluate response to fertirelin acetate dosages and to determine difference (LSD: 0.05) and bioequivalence (alpha = 0.05) between the various dosages of GnRH products tested. Significant quadratic dose response relationships were detected for the LH and FSH log AUC data. Plots of the LH log AUC but not the FSH log AUC data suggested that a response plateau was being approached at the higher dosages of fertirelin acetate. Bioequivalence (alpha = 0.05) was based on the assumption that two means are equivalent if they differ by no more than 20% of the reference log AUC mean. Using these criteria fertirelin acetate is 2.5 to 10 times more potent than gonadorelin, whereas buserelin is approximately 10 to 20 times more potent than fertirelin acetate in the bovine for LH and FSH release.

Journal Article↗
PubMed1992

Follicular growth, ovulation and embryo recovery in dairy cows given FSH at the beginning or middle of the estrous cycle.

Variability in the superovulation response is an important problem for the embryo transfer industry. The objective of this study was to determine whether FSH treatment at the beginning of the cycle would improve the ovulation rate and embryo yield in dairy cows. Twenty-eight postpartum cyclic dairy cows were allocated at random to 4 treatment groups (A, B, C and D). Group A cows (n=10) received FSH (35 mg) at a decreasing dose, starting on Day 9 (Day 0=day of estrus) for 5 days followed by PGF2alpha (35 mg) on Day 12. Cows assigned to Groups B, C and D (n=6 cows each, respectively) were given 35 mg FSH at a decreasing dose from Days 2 to 6 followed by PGF2alpha on Day 7. Group C and D cows received PRID inserts from Day 3 to Day 7. Cows in Group D additionally received 1000 IU hCG 60 hours after PGF2alpha treatment. Ovaries were scanned daily using a real time ultrasound scanner from the beginning of FSH treatment until embryo recovery, to monitor follicular development, ovulation and the number of unovulated follicles. Embryos were recovered from the uterus by a nonsurgical flushing technique 7 days after breeding. There were no differences (P>0.01) in the number of follicles>10 mm at 48 hours after PGF2alpha treatment among the 4 groups. The mean numbers of follicles were 10.6+/-1.2, 9.3+/-1.3, 12.2+/-1.3 and 15.0+/-2.9 for Groups A, B, C and D, respectively. A significantly (P<0.001) higher number of ovulations was observed and a larger number of embryos was recovered in Group A than in the other groups. The results of this study indicate that superovulation with FSH at the beginning of the cycle causes sufficient follicular development but results in very low ovulation and embryo recovery rates.

Journal Article↗
PubMed1992

The effects of FSH-priming and dominant follicular regression on the superovulatory response of cattle.

Thirty superovulatory treatments were administered to 19 mixed-breed, nonlactating cows. In 10 superovulatory treatments, the cows were primed with follicle stimulating hormone (FSH) on the second and third day of the estrous cycle, and in another 10 superovulatory treatments, the cows received no priming dosage of FSH. Initiation of the superovulatory treatments in both groups was determined by ultrasonically monitoring for regression of the dominant anovulatory follicle. Still another 10 superovulatory treatments were begun on Day 10 without regard for regression of the dominant anovulatory follicle and without a priming dosage of FSH. The mean days for starting the superovulatory treatment in the FSH-primed cows, in the nonprimed cows and in the controls were 10.5, 11.9 and 10 days, respectively. All cows were treated with eight injections of FSH at 12-hour intervals in a declining dosage (36 mg total). Cows were bred naturally and embryos collected nonsurgically seven days later. There was no significant difference (P>0.05) between the total number of embryos or transferable embryos in the three treatment groups. In this study neither priming on Days 2 or 3 nor initiating the superovulatory treatment, based on the morphologic regression of the dominant anovulatory follicle, was an effective means for improving the superovulatory response in cattle.

Journal Article↗
PubMed1994

Follicular development and superovulation response in cows administered multiple FSH injections early in the estrous cycle.

To determine whether follicular development, superovulation and embryo production were affected by the absence or presence of a dominant follicle, cows were administered injections of FSH twice daily in the early (Days 2 to 6, estrus=Day 0) or middle stage (beginning on Day 10 or 11) of the estrous cycle. Treatment with FSH early in the cycle stimulated follicular development in 83 to 100% of all cows from 4 groups evaluated at different times after PGF2alpha treatment on Days 6 and 7. However, the proportion of cows with >2 ovulations varied from 31 to 62.5%, indicating that induction of follicular development may occur in the absence of superovulation. When compared with cows treated in the middle of the cycle, no differences were observed in the proportion of cows with >2 ovulations (31 vs 20%), ovulation rate. (26.0+/-6.3 vs 49.6+/-25.8), production of ova/embryos (13.3+/-3.2 vs 14.4+/-3.4), or the number of transferable embryos (8.0+/-3.6 vs 5.4+/-1.5; early vs middle, respectively). The proportion of the total number of embryos collected that were suitable for transfer was greater (P<0.01) in cows treated early in the cycle (60%) than at midcycle (37.5%). The diameter of the largest follicle observed by ultra-sound prior to initiation of FSH treatment in the early stage of the cycle (10.0+/-2.0 mm) was smaller (P<0.05) than at midcycle (16.8+/-1.3 mm). These results demonstrate that superinduction of follicular development is highly consistent after FSH treatment at Days 2 to 6 of the cycle and that superovulation and embryo production are not less variable than when FSH is administered during the middle of the cycle. However, superovulation in the early stage of the cycle may increase the proportion of embryos suitable for transfer.

Journal Article↗
PubMed1994

Follicular and FSH responses to parturition during the anovulatory season in mares.

The ovaries of periparturient pony mares (n=9 to 16 parturitions per month for January to April) were scanned ultrasonically on the day of parturition, while those of postpartum and control mares (n=12) were examined at least twice weekly. Four mares had apparent lactational anovulation (incidence, 7%) that corrected spontaneously (1 mare) or within 14 d after the weaning of foals on August 10 (3 mares). All but 2 of the postpartum ovulations occurred after April 29; that is, parturition did not effectively stimulate ovulation in ponies foaling during the anovulatory season. Mean diameter of the largest follicle per month increased (P<0.001) progressively in the controls (means: 11.4, 14.4, 19.0 and 24.5 mm for January to April, respectively). In the parturient mares, the diameter of the largest follicle on day of parturition did not increase over months (range of means: 13.6 to 16.9 mm), indicating that a suppressive effect of pregnancy counteracted the stimulatory effect of season. Within each month of parturition, diameter of the largest follicle increased (P<0.05) between Day 0 (day of parturition) and Day 3 or 7. Blood samples for FSH assay were taken daily for 14 d from 6 mares with parturition in the middle of each month and from 6 controls on the corresponding calendar days. In periparturient mares, a significant increase in mean FSH concentrations occurred for all months of parturition between Day-2 and Day 0, followed by a significant decrease between Day 3 and Day 7. Maximum means for the periparturient FSH profile were temporally related to the beginning of follicular growth. In the controls, FSH concentrations were not affected by month or day, or by their interaction. Within each month, mean FSH concentrations were lower (P<0.05) in the periparturient mares than in the controls (averaged over all months: 3.9+/-0.1 versus 7.9+/-0.3 ng/ml) even though follicular growth was greater following parturition than during the corresponding calendar days in controls.

Journal Article↗
PubMed1994

Decreased pulsatile LH secretion in heifers superovulated with eCG or FSH.

This study was designed to test the hypothesis that treatment with super-ovulatory drugs suppresses endogenous pulsatile LH secretion. Heifers (n=5/group) were superovulated with eCG (2500 IU) or FSH (equivalent to 400 mg NIH-FSH-P1), starting on Day 10 of the estrous cycle, and were injected with prostaglandin F(2alpha) on Day 12 to induce luteolysis. Control cows were injected only with prostaglandin. Frequent blood samples were taken during luteolysis (6 to 14 h after PG administration) for assay of plasma LH, estradiol, progesterone, testosterone and androstenedione. The LH pulse frequency in eCG-treated cows was significantly lower than that in control cows (2.4 +/- 0.4 & 6.4 +/- 0.4 pulses/8 h, respectively; P<0.05), and plasma progesterone (3.4 +/- 0.4 vs 1.8 +/- 0.1 ng/ml, for treated and control heifers, respectively; P<0.05) and estradiol concentrations (25.9 +/- 4.3 & 4.3 +/- 0.4 pg/ml, for treated and control heifers, respectively; P<0.05) were higher compared with those of the controls. No LH pulses were detected in FSH-treated cows, and mean LH concentrations were significantly lower than those in the controls (0.3 +/- 0.1 & 0.8 +/- 0.1, respectively; P<0.05). This suppression of LH was associated with an increase in estradiol (9.5 +/- 1.4 pg/ml; P<0.05 compared with controls) but not in progesterone concentrations (2.1 +/- 0.2 ng/ml; P>0.05 compared to controls). Both superovulatory protocols increased the ovulation rate (21.6 +/- 3.9 and 23.0 +/- 4.2, for eCG and FSH groups, respectively; P>0.05). These data demonstrate that super-ovulatory treatments decrease LH pulse frequency during the follicular phase of the treatment cycle. This could be explained by increased steroid secretion in the eCG-treated heifers but not in FSH-treated animals.

Journal Article↗
PubMed1995

Effects of fetal bovine serum, FSH and 17beta-estradiol on the culture of bovine preantral follicles.

We describe a 7-d culture in droplets of collagen gel of isolated small bovine preantral follicles in medium with or without 10% fetal bovine serum (FBS). In addition, the effect of human recombinant FSH and 17beta-estradiol on the morphology and growth of the preantral follicles was investigated in medium without FBS. After culture in medium with 10% FBS, the increase in follicle diameter was 13.1 +/- 8.4 microm, the percentage of BrdU-labeled cells was 49.9 +/- 11.3 and the number of cells per area granulosa was 11.1 +/- 1.8. Omission of serum from the culture medium had no effect on the percentage of labeled cells, but the diameter increase was lower and the cells were smaller. Apparently, serum affects the size of the granulosa cells from small preantral follicles rather than the stimulation of cell proliferation. Addition of human recombinant FSH and/or 17beta-estradiol to serum-free medium resulted in a larger diameter increase during culture compared with that of the control. With FSH, this was due to an increase in cell proliferation, while with estradiol this was caused by an increase in granulosa cell size. The effects of simultaneous treatment with FSH and estradiol was simply the combination of their individual effects. In conclusion, small bovine preantral follicles can be cultured for 7 d in the absence of serum and hormones. The follicles increase in diameter and react to FSH with enhanced cell proliferation and to estradiol with an increase in cell size.

Journal Article↗
PubMed1996

Effects of LH administration at the end of an FSH superovulatory regimen on ovulation rate and embryo production in three breeds of sheep.

In 3 experiments, 168 ewes of Manchega (n = 72), Churra (n = 62), and Merina (n = 34) breeds were used to test the hypothesis that administration of pure LH, coincident with progestogen removal during superovulation with FSH, causes an increase in the ovulation rate and number of embryos. This administration of LH can further interact with genotype, resulting in breed differential response. In each experiment, the animals were randomly assigned to 1 of 3 treatments. Estrus in all sheep was synchronized with intravaginal sponges of 30 mg of FGA for 12 d, then 270 microg of FSH were administered in 6 injections at 12-h intervals in decreasing doses, starting 48 h before sponge removal. The FSH/LH ratio of the original preparation was 3, and remained constant throughout the treatment in the control group (C). In Treatment 1, (T1) and Treatment 2, (T2), pure LH was administered coincident with progestogen removal-5th FSH injection, and with the 6th FSH injection, at 2 dose levels: 60 and 120 microg, (T1), and 120 and 240 microg (T2). Mating occurred 36 and 48 h after the progestogen removal, and the embryos were surgically collected and morphologically evaluated on Days 7 and 8 after sponge withdrawal. Overall, the results showed that LH administration at the end of the FSH treatment did not increase the ovulation rate and number of embryos in Merino (5.9 +/- 1.4 and 5.6 +/- 1.4, respectively, T1; 7.0 +/- 1.0 and 5.7 +/- 1.2, T 2; 4.9 +/- 1.1 and 2.6 +/- 0.7, C), Churra (6.8 +/-1.4 and 5.2 +/- 1.4, T1; 8.1 +/- 1.5 and 6.3 +/- 1.4, T2; 6.1 +/- 1.5 and 5.4 +/- 1.3, C) and Manchega (6.0 +/- 1.0 and 4.4 +/- 1.0, T1; 5.0 +/- 0.8 and 4.2 +/- 0.8, T2; 4.8 +/- 1.5 and 3.8 +/- 1.0, C). Administration of LH induced a significant (P < 0.05) increase in the frequency of multiple ovulations (72.3 +/- 4.3 %, T1; 74.1 +/- 11.5 %, T2; 55.6 +/- 5.9 %, C) paralleled to a decrease in the occurrence of ewes with no ovulations (8.7 +/- 2.6 %, T1; 7.6 +/- 4.6 % T2; 17.3 +/- 3.2 %, C) or 1 to 2 ovulations (18.7 +/- 4.6 %, T1; 18.1 +/- 7.5 %, T2; 26.8 +/- 5.8 % C), regardless of breed or dose of LH. No increase in the mean number of viable embryos was observed, probably due to both the high individual variability and the lower fertilization rates observed in sheep showing multiple ovulations.

Journal Article↗
PubMed1981

Plasma and pituitary concentrations of LH, FSH and prolactin after injection of GnRH in aged female C57BL/6 mice.

Plasma and pituitary concentrations of LH, FSH and prolactin (Prl) were compared by radioimmunoassay (RIA) in young mature (2-4 month-old) and aged (16-22 month-old) female C57BL/6 mice, following various experiments with IP injections of GnRH. Unanesthetized mice were bled by cardiac puncture either (1) at various time intervals following a single injection of 25 ng GnRH, (2) after several injections of 25 ng GnRH, or (3) after receiving excessively large doses of GnRH. From the RIA of plasma and pituitary concentrations of LH, it appeared that the pituitaries of aged mice were, in general, capable of responding to GnRH treatment, only to a lesser degree than that of the younger females. The exception was that the pituitaries of aged mice that were subjected to unusually high doses of GnRH continued to secrete higher levels of LH, whereas the response of the pituitaries in younger mice plateaued after receiving 25 ng GnRH. Plasma and pituitary concentrations of FSH and Prl remained fairly constant when aged GnRH-treated females were compared with aged controls. This was also true when FSH and Prl concentrations in the younger mice were compared with their controls, except for significantly higher plasma FSH and significantly lower pituitary FSH following several injections of GnRH. When the hormonal concentrations of the young and aged groups were compared in the various experiments, the older mice consistently exhibited higher levels of gonadotropin and lower levels of prolactin than those of the younger mice. In a separate experiment, in which a radioreceptor assay (RRA) was used to quantitate plasma LH in GnRH-treated mice, both age groups were found to have lower concentrations of LH (p less than 0.05) than those obtained by RIA from the same animals. The RRA to RIA ratio, however, was 0.84 for 2-4 month-old and 0.57 for 16-22 month-old mice. These studies suggest that the anterior pituitary of the aged mouse is less sensitive to GnRH stimulation.

Aging↗
PubMed1976

Site at which FSH regulates estradiol-17beta biosynthesis in Sertoli cell preparations in culture.

Sertoli cells were isolated from testes of 20-day-old rats and were maintained in primary culture. The ability of these cells to synthesise estradiol-17beta from a variety of exogenous substrates, progesterone, testosterone,androstenedione, 19-hydroxyandrostenedione and 19-hydroxytestosterone in the presence and absence of follicle-stimulating hormone (FSH) was examined. In the presence of each of the substrates alone for 24 h the rate of estradiol-17beta synthesis was very low. FSH (NIH-FSH-S11, 5 mug/ml) stimulated estradiol-17beta synthesis 75-fold when added to medium containing testosterone (5 X 10(-7)M) but caused only marginal stimulation when added to medium containing progesterone (5 X 10(-7) M). Both FSH and dibutyryl cyclic AMP (bu2cAMP) stimulated the conversion of each of the substrates, androstenedione, 19-hydroxyandrostenedione and 19-hydroxytestosterone to estradiol-17beta, and the effects were similar to those observed in the presence of testosterone. These data indicate that, under the culture conditions employed, progesterone is not an effective substrate for conversion to estradiol-17beta by Sertoli cells. Estradiol-17beta synthesis was stimulated by FSH in the presence of the C19 steluences the conversion of androgens to estrogens, either directly or indirectly, at the aromatisation step (i.e. the conversion of 19-hydroxylated androgens to estrogens).

Androstenedione↗
PubMed1977

Studies on the synergistic effect of androgen on the stimulation of progestin secretion by FSH in cultured rat granulosa cells: progesterone metabolism and the effect of androgens.

Metabolic transformations of progesterone in cultures of granulosa cells from immature hypophysectomized rats treated with diethylstilbestrol were studied in relation to the synergistic action of exogenous androgen and FSH on progestin (progesterone and 20alpha-dihydroprogesterone) accumulation. Androstenedione (Ad; 10 ng/ml) enhanced the sensitivity of rat granulosa cells to this steroidogenic action of FSH, lowering the threshold of the response from greater than 4 ng/ml (FSH alone) to 0.8 ng/ml in the presence of Ad. A synergistic effect with FSH was also shown by various 5alpha-androstane derivatives. They were, however, less effective than the parent delta4-3 keto androstenes. Progesterone underwent extensive 5alpha-reduction during culture, leading to accumulation of endogenous 5alpha-pregnane compounds, and to transformation of labelled progesterone into 5 alpha-reduced radiometabolites. These compounds corresponded in gas-liquid and thin-layer chromatographic behaviour to 3alpha-hydroxy-5alpha-pregnan-20-one, 20alpha-hydroxy-5alpha-pregnan-3-one and 5alpha-pregnane-3alpha,20alpha-diol. The rate of 5alpha-reduction of progestins was not affected by the presence of exogenous Ad (1 microgram/ml), ruling out the possibility that the effect of androgen on progestin accumulation depends on competitive inhibition of 5alpha-reductase. An involvement of androgen of thecal origin in the enhancement of the sensitivity of the FSH-responsive mechanism in granulosa cells is suggested.

20-alpha-Dihydroprogesterone↗
PubMed1978

Reduction in FSH receptors in the rat testis by injection of homologous hormone.

Intratesticular injection of 25 microgram rat FSH into rats under continuous urethane anaesthesia resulted 24 h later in a 50% reduction in binding sites for FSH in testicular homogenates. By 48 h after injection, receptor number usually returned to control values. Intratesticular injection of 125I-labelled rat RSH showed less than 1% remaining in the testis 24 h later, suggesting that the reduction in receptor numbers at 24 h is not due to occupancy by the FSH. Experiments did not suggest that the injection of FSH induced FSH-degrading enzymes or inhibitors of binding.

Animals↗
PubMed1981

Control of estrogen synthesis in the testis of the infant rat by FSH and androgen.

The experiments studied the ability of androgens to stimulate in vivo the production of estradiol by the testes of the 12-day-old rat as well as interactions between FSH and androgens in this regard. The content of testosterone and estradiol in the testes was measured by RIA of methanolic extracts which were purified on columns of Sephadex LH-20. It was found that androstenedione, testosterone and 19-hydroxytestosterone were able to stimulate estradiol formation in the testes; the response was optimal 3 h after s.c. injection. The stimulatory effect was absent after injection of 5 alpha-reduced androgens. It was concluded that the ability of a single injection of androgen to increase the content of estradiol in the testes was due to provision of additional substrate for aromatization by the Sertoli and/or Leydig cells. Priming of rats for 2 days with testosterone (60 microgram/g bw daily) resulted in a reduction of concentration of LH and FSH in plasma and was associated with an inhibition of the estradiol response to a subsequent injection of testosterone. If priming with testosterone was followed by an injection of FSH, more estradiol was formed than when the FSH injection was preceded by an oil or dihydrotestosterone priming regimen. It was concluded that the inhibition of testosterone-induced aromatization noted after testosterone priming was due to low gonadotropin secretion rather than a direct effect on the testis and that priming of the infant rat with androgen enhanced the response to FSH because such treatment provided additional substrate for aromatization.

Androgens↗
PubMed1982

Modulation of prolactin receptors in cultured rat granulosa cells by FSH, LH and GnRH.

The hormonal modulation of prolactin (PRL)-binding capacity of rat granulosa cells was studied. Granulosa cells obtained from immature, hypophysectomized, estrogen-treated rats were cultured for 2 days in a serum-free medium in the presence of various hormones. FSH treatment in vitro stimulated granulosa cell PRL-binding capacity by approximately 4-6-fold in a dose-dependent manner. Concomitant treatment with 10-8 M GnRH inhibited the FSH-induced increase in PRL-binding capacity by 64%. In contrast, the inhibitory effect of GnRH was blocked by concomitant treatment with 10-6 M of a GNRH antagonists, [D-pGlu1, D-Phe2, D-Trp3,6]GnRH. PRL-binding capacity was also increased (approximately 2-fold) by in vitro treatment with cholera toxin (10 microgram/ml). In granulosa cells pre-treated with FSH in vitro for 2 days, hCG treatment for 2 additional days stimulated PRL-binding capacity in a dose-dependent manner (approximately 2-fold). Likewise, treatment with LH (100 ng/ml) also stimulated PRL-binding capacity by approximately 2-fold. These in vitro studies demonstrated that gonadotropins (FSH, LH and hCG) directly enhanced PRL binding by granulosa cells, whereas GnRH inhibited FSH action.

Animals↗
PubMed1986

Melatonin's differential inhibition of FSH and LH release from hamster pituitary glands.

Melatonin initially inhibited FSH secretion from superfused adult male hamster anterior pituitary glands obtained at 8:30 a.m. However, there was a gradual rebound during melatonin superfusion followed by an overshoot above baseline when melatonin was discontinued (morning response). Melatonin continuously inhibited FSH secretion during superfusion of hamster anterior pituitary glands obtained at 3:30 p.m., with a rebound evident only when melatonin was withdrawn (afternoon response). Melatonin continuously inhibited LH secretion from these superfused pituitaries, with a return to baseline levels only upon melatonin withdrawal. Prior pinealectomy or constant light could reverse the FSH morning response to an afternoon response, and late-morning melatonin injections could reverse the FSH afternoon response to a morning response. Neither prior pinealectomy, constant light nor melatonin injections affected melatonin inhibition of LH secretion from superfused pituitary glands. These results suggest that melatonin differentially inhibits FSH and LH secretion from isolated superfused hamster anterior pituitary glands.

Animals↗
PubMed1986

Effect of melatonin in vivo upon FSH and LH release from hamster pituitary glands.

The effect of chronic daily afternoon injections of melatonin upon basal and melatonin-modulated release of FSH and LH was investigated in superfused hamster anterior pituitary glands. The basal release rate of both FSH and LH began to decline following the beginning of melatonin injections, and reached a nadir after six weeks. Basal release rate of FSH and LH then began to spontaneously increase and reached a plateau at 13 weeks of injections. The inhibition by melatonin upon FSH and LH release in vitro gradually declined during the period of melatonin injections. After six weeks of melatonin injections the release rate of FSH was no longer suppressed by melatonin superfusion, while the release rate of LH became refractory to melatonin suppression in vitro after nine weeks of melatonin injections. These results demonstrate a change in the release rates of both basal and melatonin-inhibited gonadotropin release during melatonin-induced testicular regression and recrudescence in hamsters.

Animals↗