Independent actions of gonadotropin releasing hormone upon cyclic GMP production and luteinizing hormone release

Gonadotropin releasing hormone (GnRH) and its potent analog [D-Ser(tBu)6]des-Gly10-GnRH N-ethylamide elevate pituitary cyclic GMP levels while stimulating gonadotropin release in cultured pituitary cells. Addition of mycophenolic acid to pituitary cell cultures decreased basal and GnRH-induced cGMP production to undetectable levels, but did not reduce basal or GnRH-stimulated luteinizing hormone (LH) release. Elevation of endogenous cGMP levels by sodium nitroprusside, or addition of cGMP or its potent derivatives, was also without effect on basal or GnRH-stimulated LH release. These findings demonstrate that the elevation of intracellular cGMP during GnRH action does not mediate the release of LH by pituitary cells.     

The effect of luteinizing hormone, human chorionic gonadotropin and adrenocorticotropic hormone on puberty in gilts reared in confinement

Three trials were conducted to determine the effect of human chorionic gonadotropin (HCG), luteinizing hormone (LH) and adrenocorticotrophic hormone (ACTH) on the incidence of estrus in gilts which were reared in confinement, relocated and exposed to a boar. In trial 1, 33 gilts were given saline or 250 IU HCG at an average age of 191 days and then relocated and observed for estrus twice daily for 10 days. Treatment with HCG did not increase the proportion of gilts that exhibited estrus. In trial 2, 42 gilts were relocated at an average age of 200 days. The gilts were assigned to three treatment groups and injected with saline, 68 mug LH or 1 mg LH. After 10 days of estrous detection, a laparoscopic examination of the ovaries was conducted on all gilts failing to exhibit estrus. In groups 1 to 3, the proportions of gilts exhibiting estrus or ovulating during the 10 days after treatment were 13 of 21, 6 of 10, and 5 of 11, respectively. In trial 3, 12 gilts were relocated to pasture lots, given saline or 80 IU ACTH twice daily for 2 days and checked for estrus for 14 days. The proportions of gilts that exhibited estrus after the administration of saline or ACTH were 4 of 6 and 6 of 6, respectively. The results indicate that the incidence of estrus in gilts reared in confinement, relocated and exposed to a boar was not affected by pre-treatment with exogenous HCG, LH or ACTH.     

The effect of luteinizing hormone releasing hormone and anti-luteinizing hormone releasing hormone antibodies on chorionic gonadotropin and progesterone secretion by human placental villiin vitro

Gonadotropin releasing hormone has been located and found to be secreted by the human placenta in culture. Addition of the releasing hormone upto 1μg concentration in the placental cultures brings about stimulation of chorionic gonadotropin and progesterone secretion. Higher amounts of the decapeptide has an inhibitory influence on both the gonadotropin and the steroid production. The action of the releasing hormone on the placenta could be blocked by the anti-luteinizing hormone releasing hormone monoclonal antibodies indicating a possible site of action of the antibodies for control of fertility     

Ovarian response to human chorionic gonadotropin or gonadotropin releasing hormone in cats in natural or induced estrus

Human chorionic gonadotropin (hOG) or gonadotropin releasing hormone (GnRH) was given alone or with repeated coital stimuli to study ovarian activity and ovulation in the domestic cat. Adult cats in natural estrus (NE) or treated with follicle stimulating hormone (FSH-P) to induce estrus (2.0 mg/d for 5 d; IE) were assigned to one of five treatments: I, mating (M) only (three times daily for the first 3 d of estrus); II, M + hOG (250 IU, i.m. on Days 2 and 3 of estrus); III M + GnRH (25 mug, i.m. on Days 2 and 3 of estrus); IV, hOG only (250 IU, i.m. on Days 2 and 3 of estrus); or V, GnRH only (25 mug on Day 2 and 3 of estrus). Overall, IE females produced a greater (P < 0.05) number of corpora lutea (7.6 +/- 0.9) and unovulated follicles (18.9 +/- 2.1) than NE cats (4.9 +/- 0.6 and 3.6 +/- 0.9, respectively). For both NE and IE females, the M + hOG treatment (II) produced a greater number (P < 0.05) of ovulations (9.1 and 13.9, respectively) than any other ovulatory regimen (I, 4.1, 6.6; III, 4.1, 7.8; IV, 4.0, 6.2; V, 4.1, 5.6, respectively). These results indicate that 1) the excessive follicle number resulting from FSH-P treatment cannot be reduced with any of the hOG or GnRH treatments tested and 2) the use of hOG with copulatory stimuli synergistically enhances the ovulatory response of cats experiencing a natural estrus or those treated with FSH-P.     

Effects of testosterone, dihydrotestosterone and estradiol on gonadotropin release after gonadotropin releasing hormone administration in cyclic mares

Sixteen intact cyclic mares were treated on the fourth day of estrus and then every other day for a total of six injections with 1) testosterone propionate, 2) dihydrotestosterone (DHT) benzoate, 3) estradiol (E2) benzoate or 4) safflower oil. Mares were given gonadotropin releasing hormone (GnRH) on Day 3 of estrus (pretreatment) and again 24 h after the last steroid or oil injection. Treatment with testosterone propionate resulted in a greater (P less than 0.05) follicle-stimulating hormone (FSH) response to the second injection of GnRH compared with all other treatments. Treatment with DHT benzoate also resulted in greater (P less than 0.05) FSH response to GnRH compared with control and E2 benzoate-treated mares. Testosterone propionate and E2 benzoate administration suppressed (P less than 0.05) the normal diestrous rise in FSH concentrations exhibited by the control and DHT benzoate-treated mares. Steroid treatment did not affect the luteinizing hormone (LH) response to GnRH, although testosterone propionate treatment did suppress concentrations of LH in daily blood samples during Days 3 to 6 of treatment. It is concluded that testosterone's effect on FSH after GnRH treatment observed in this and previous experiments can be attributed to two different properties of the hormone or its metabolites acting simultaneously. That is, testosterone increased the secretion of FSH in response to GnRH as did DHT (an androgenic effect). At the same time, testosterone suppressed FSH concentrations in daily blood samples in a manner identical to that of E2 benzoate (an estrogenic effect).     

Plasma luteinizing hormone concentrations in cows given repeated treatments or three different doses of gonadotropin releasing hormone

We hypothesized that: (i) repeated GnRH treatments would increase the magnitude and duration of the LH surge and would increase progesterone (P4) concentrations after ovulation; and (ii) the release of pituitary LH would be greater in response to larger doses of GnRH. In Experiment 1, ovary-intact cows were given an intravaginal P4 (1.9 g) insert (CIDR) for 10 d and 500 μg cloprostenol (PGF) at CIDR removal to synchronize estrus. On Days 7 or 8 after estrus, cows received two PGF treatments (12 h apart) and 100 μg GnRH at 36 (Control), 36 and 38 (GnRH38), or 36 and 40 h (GnRH40) after the first PGF. Mean plasma LH concentration (ng/mL) was greater (P < 0.05) in GnRH38 (8.8 ± 1.1) than in Control (5.1 ± 1.3), with that in GnRH40 (5.8 ± 1.3) being intermediate. Although the duration (h) of the LH surge was longer in GnRH40 (8.0 ± 0.4) than in either GnRH38 (P < 0.05; 7.0 ± 0.3) or Control (P < 0.09; 7.1 ± 0.4), mean postovulatory P4 (ng/mL) was greater (P < 0.01) in Control (4.2 ± 0.7) than in GnRH38 (2.9 ± 0.6) or GnRH40 (3.0 ± 0.7) cows. In Experiment 2, ovariectomized cows were given a CIDR for 10 d and 2 mg of estradiol cypionate im at CIDR insertion. Thirty-six hours after CIDR removal, cows received, 50, 100, or 250 μg of GnRH. Cows given 250 μg GnRH released more LH (9.4 ± 1.4 ng/mL) than those given 50 or 100 μg (6.1 ± 1.3 and 5.4 ± 1.4 ng/mL, respectively), and had an LH surge of longer duration than those given 50 μg (6.8 ± 0.4 vs. 5.1 ± 0.3 h). In summary, ovary-intact cows in the GnRH38 group had greater mean and peak LH concentrations, but subsequent plasma P4 concentrations were lower than in Control cows. Ovariectomized cows given 250 μg GnRH had a greater pituitary release of LH.     

Effect of a potent gonadotropin releasing hormone antagonist on pulsatile testosterone and gonadotropin secretion in the male nonhuman primate

A potent gonadotropin releasing hormone (GnRH) antagonist [Ac-delta 3Pro1, pFDPhe2, DTrp3,6]-GnRH was given to adult male monkeys to determine the acute effect on pulsatile testosterone and gonadotropin secretion. Blood was drawn at 30 min intervals over 54 h without anesthesia using a mobile vest and tether assembly to support an indwelling catheter. After a 6 h control period, 0.1, 1.0, 2.0, 4.0 mg GnRH antagonist/kg bw in 1 ml corn oil sc, was given to intact adult male monkeys. The highest dose of GnRH antagonist decreased circulating testosterone within 6 h and for approximately 24-36 h duration. These data demonstrate that this GnRH antagonist can reduce serum testosterone both acutely and for intervals greater than 24 h and that the effective dose in intact animals is several-fold (up to 20 times) greater than in castrate animals.     

Differential response of testis and serum gonadotropins to testosterone in rats treated with a gonadotropin releasing hormone antagonist or estradiol 17 beta.

Adult rats treated with a GnRH antagonist (Ac D2Nal1, D4Cl Phe2, DTrp3, DArg6, DAla10 GnRH; code: 103-289-10, National Institutes of Health, USA) for 5 weeks (250 micrograms/kg b.w) showed multiple degrees of impairment and atrophy of the genital organs concomitant with decreased serum levels of testosterone, LH and FSH. Inhibition of spermatogenesis was characterized by germ cell degeneration and overall decline in different cell numbers and in particular, spermatids of any kind were completely absent. Testosterone supplementation (60 micrograms/rat/day, sc) to GnRH antagonist treated rats, for the same period, significantly elevated the weights of the sex organs, and the serum levels of hormones. Spermatogenesis was improved both qualitatively and quantitatively; albeit failed to be restored back to control levels. Treatment with estradiol 17 beta (1 microgram/rat/day) for 5 weeks had insignificant effect on spermatogenesis but the weights of the genital organs (seminal vesicles by 19% and ventral prostate by 40%) and the levels of serum hormones (LH by 24%, FSH 22% and testosterone by 25%) were otherwise reduced. Administration of testosterone either alone or in combination with estradiol 17 beta had only a marginal effect on spermatogenesis or on other reproductive parameters. The results indicate a positive shift in the response of the testis and serum levels of gonadotropins to testosterone supplementation in rats treated with either GnRH antagonist or estradiol 17 beta.     

Dissociation of cyclic AMP accumulation from that of luteinizing hormone (LH) release in response to gonadotropin releasing hormone (GnRH) and cholera enterotoxin.

Anterior hemipituitaries from female rats were incubated $\text{in}\text{vitro}$ in Krebs Ringer bicarbonate buffer, pH 7.2 containing 2 mg/ml of glucose in the absence and in the presence of GnRH or cholera enterotoxin. Following this incubation, the pituitaries were separated from the medium and cAMP and LH were assayed in the tissue and the medium, respectively. Incubations with GnRH in the range of 25 ng/ml to 400 ng/ml resulted in increase in LH release into the medium. Cholera enterotoxin at a concentration of 1 μg/ml, by contrast, caused no release of LH into the medium, but caused a 5-fold increase in cAMP level and this effect was concentration dependent. Cholera enterotoxin did not interfere with the GnRH-mediated LH release. It is concluded from these experiments that the ability of GnRH to increase cAMP level may be independent of its ability to release LH.     

Effects of hyper- and hypoprolactinemia on gonadotropin secretion, rat testicular luteinizing hormone/human chorionic gonadotropin receptors and testosterone production by isolated Leydig cells

The effect of prolactin (Prl) on gonadotropin secretion, testicular luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors, and testosterone (T) production by isolated Leydig cells has been studied in 60-day-old rats treated for 4 days, 4 and 8 weeks with sulpiride (SLP), a dopaminergic antagonist, or for 4 days and 4 weeks with bromocriptine (CB), a dopaminergic agonist. Plasma Prl concentrations were significantly greater in the SLP groups (204 +/- 6 ng/ml) and lower in the CB groups (3.0 +/- 0.2 ng/ml) than those measured in the control groups (54 +/- 6 ng/ml). The plasma concentrations of gonadotropin were not affected by a 4-day treatment with SLP or CB, nor were they after a 4-week treatment with CB. However, the hyperprolactinemia induced by an 8-week treatment with SLP was associated with a reduced secretion of gonadotropin (LH, 16 +/- 4 vs. 35 +/- 6 ng/ml; FSH, 166 +/- 12 vs. 307 +/- 14 ng/ml). In SLP-induced hyperprolactinemia, a 30% increase in the density of the LH/hCG testicular binding sites was observed (178 +/- 12 fmol/mg protein), whereas a 60% decrease was measured in hypoprolactinemia (55 +/- 5 vs. control 133 +/- 5 fmol/mg protein). Plasma T levels were increased in 4-day and 4-week hyperprolactinemic animals (4.3 +/- 0.4 and 3.9 +/- 0.4 ng/ml, respectively), but returned to normal levels in the 8-week group (3.0 +/- 0.5 vs. C: 2.3 +/- 0.2 ng/ml). No T modifications were observed in hypoprolactinemic animals. Two distinct populations of Leydig cells (I and II) were obtained by centrifugation of dispersed testicular cells on a 0-45% continuous Metrizamide gradient. Both possess LH/hCG binding sites. However, the T production from Leydig cells of population II increased in the presence of hCG, whereas that of cell population I which also contain immature germinal cells did not respond. The basal and stimulated T secretions from cell populations I and II obtained from CB-treated animals were similar to controls, whereas from 4 days to 8 weeks of hyperprolactinemia, basal and hCG induced T productions from cell population II decreased progressively. These data show that hyperprolactinemia causes, in a time-dependent manner, a trophic effect on the density of LH/hCG testicular receptors; reduces basal and hCG-stimulated T production from isolated Leydig cells type II; and results in an elevated plasma T concentration which decreases with time. The latter suggests a slower T catabolism and/or an impaired peripheral conversion of T into 5 alpha-dihydrotestosterone (DHT). Although hypoprolactinemia is associated with a marked reduction in testicular LH receptors, it does not affect T production.     

Relationship between serum luteinizing hormone and estradiol in prepubertal boars

Effects of estradiol on serum luteinizing hormone (LH) were studied in prepubertal boars. In Exp. 1, 15-wk-old boars were given (iv) 50 mug estradiol, 1 mg testosterone or 1.5 ml ethanol. Estradiol (P<0.05) decreased LH over a 2.5-hr period, but testosterone did not. In Exp. 2, an estradiol implant reduced LH sample variance (P<0.01) while LH (547 +/- 96 vs 655 +/- 43 pg/ml) and estradiol (14.2 +/- 3.3 vs 18.4 +/- 1.0 pg/ml; control vs implant) were unchanged in 12-wk-old boars. Pulsatile LH releases (4.3 +/- 1.1 vs 3.0 +/- 0.4 pulses/pig/8 hr; control vs treated) and pulse amplitude (272 +/- 34 vs 305 +/- 40 pg/ml) were not affected. The implant tended to decrease serum testosterone (4.86 +/- 0.75 vs 7.66 +/- 1.51 ng/ml; P<0.10). In Exp. 3, LH was higher after zero implants than after four implants (279 +/- 7 vs 227 +/- 9 pg/ml; P<0.01), and LH after two implants was also higher than after four implants (263 +/- 7 pg/ml; P<0.01) in 14-wk-old boars in a Latin square design. Peak LH after 40 mug gonadotropin releasing hormone (GnRH) was less after two and four implants (1,100 +/- 126 and 960 +/- 167 pg/ml, respectively; P<0.01) than after zero implants (1,742 +/- 126 pg/ml). Slope of the first 20 min of LH response to GnRH was greater after zero implants (45.3 pg/min; P<0.05) than after either two or four implants (20.6 and 16.9 pg/min, respectively). Implant treatment decreased serum testosterone (P<0.025) but increased estradiol (P<0.10). Small changes in serum estradiol resulted in changes in LH. These changes in sample variance and mean LH were recognized by boars as different from normal because serum testosterone decreased. Changes in LH may result from estradiol's negative effect on pituitary responsiveness to endogenous GnRH because response to exogenous GnRH was depressed by estradiol.     

Epididymal phenotype in luteinizing hormone receptor knockout animals and its response to testosterone replacement therapy

Previous studies reported that epididymis contains functional LH receptors. The LH receptor knockout mice, which have epididymal phenotypes, gave us an opportunity to test the hypothesis that testosterone replacement alone may not be sufficient to reverse phenotypes to wild-type epididymis. The morphological phenotype in knockout animals includes a decrease in luminal diameter of the proximal and distal caput and cauda epididymis, the absence of clear and halo cells in the epithelial lining, a decrease in the height of principal cells and the number of cells containing cilia, a decrease in cilia length, and a change from basal to central location of nuclei in the principal cells. The biochemical phenotype includes a decrease in periodic acid-Schiff reaction product, reflecting the glycogen and glycoprotein synthesis and secretion, a decrease in androgen receptor (AR) and estrogen receptor (ER)beta, and an increase in ERalpha levels. Twenty-one-day testosterone replacement therapy in 30-day-old knockout animals reversed some, but not all, morphological and biochemical phenotypes. Those that did not reverse include luminal diameters of proximal and distal caput and cauda epididymis, the percentage of ciliated principal cells in caput epididymis, and nuclear AR localization. In summary, while our results reaffirm that androgens are important for normal epididymal morphology and function, they indicate that LH could be required for certain facets of epididymal morphology and/or function.     

Effect of elevating serum lipids on luteinizing hormone response to gonadotrophin releasing hormone challenge in energy-deficient anestrous heifers

A study was conducted to evaluate the effect of feeding a bypass fat on luteinizing hormone (LH) response to gonadotrophin releasing hormone (GnRH) in noncyclic Holstein heifers. Twelve cyclic Holstein heifers were fed a complete diet at 40% net energy for maintenance (NE(m)) until cessation of ovarian activity. Based on weights and condition scores, heifers were assigned to either a control or treatment diet containing 0.45 kg bypass fat and fed at an energy level of 85% NE(m). Diet adjustments were made following weekly weighings. GnRH challenges were conducted at four periods: prior to initial energy deprivation, at termination of 40% NE(m) feeding, and twice more at 21-d intervals after 85% NE(m) feeding began. Blood was sampled via a jugular catheter every 15 min for 5 h, and GnRH was injected after the fourth sample. None of the heifers exhibited estrous activity after the initial energy deprivation. Heifers on the bypass fat diet continued to lose weight during the treatment period, while the control heifers gained a slight amount of weight. Baseline and peak concentrations of LH were not significantly affected by time or diet. Time to GnRH-induced LH peak was longer (53 vs 130 min, P < 0.01) after 40% NE(m) and remained greater at all times thereafter. Serum lipid levels increased 82.5% among heifers being fed the bypass fat. Energy restriction had no effect on the magnitude of LH response to GnRH but did delay response time.     

A change from gonadotropin releasing hormone antagonist to gonadotropin releasing hormone agonist therapy does not affect the oncological outcomes in hormone sensitive prostate cancer

Background

The aim of our retrospective study was to evaluate the 5-year survival and time to castration resistant prostate cancer in patients with hormone sensitive prostate cancer treated with the gonadotropin releasing hormone antagonist, degarelix. Another aim was to evaluate the effects of changing the treatment from degarelix to a gonadotropin releasing hormone agonist after achieving stable disease control, on the clinical and oncological outcomes.

Results

Our analysis was based on the data of 108 patients with prostate cancer who were treated with degarelix. Of these, the treatment was changed from degarelix to a gonadotropin releasing hormone agonist in 57 patients (changed group), and the treatment with degarelix was continued in the other 51 (continued group). The overall 5-year survival was statistically superior in the changed (96.6%) group than that in the continued (74.1%) group (p?=?0.006). The 5-year cancer-specific survival was also superior in the changed (100%) group than that in the continued (84.6%) group (p?=?0.027). The average time to castration resistant prostate cancer was comparable in both the changed (43.3 months) and continued (35.2 months) groups (p?=?0.117). Lower serum levels of prostate specific antigen and alkaline phosphatase were maintained after changing the therapy from degarelix to a gonadotropin releasing hormone agonist.

Conclusions

Degarelix is effective in the treatment of prostate cancer. Degarelix therapy can also be safely changed to a gonadotropin releasing hormone agonist without any adverse clinical or oncological effects.