Administration Of LHRH Agonist Research Articles

Effects of Gonadotropin-Releasing Hormone and Its Agonists on Prolactin Secretion from Normal and Tumorous Pituitary Cells

Previous studies on the effect of gonadotropin-releasing hormone (LHRH) agonist on prolactin (PRL) secretion from normal and tumorous pituitary cells have not been conclusive as to the mechanism of action of these agonists. In this study the short-term administration of a LHRH agonist did not affect circulating PRL levels, but depleted the PRL content of the pituitary gland by 24, 49 and 73% after 2, 3 and 4 days, respectively, in normal female rats and by 75% after 4 days in normal male rats. This effect of the agonist could not be attributed to changes in the sex steroid environment: although plasma 17 beta-estradiol concentrations were significantly suppressed in female rats, circulating testosterone levels had not changed yet in the male rats. Interestingly, the pituitary luteinizing hormone (LH) content was depleted already from day 2 of LHRH agonist administration onwards, while the follicle-stimulating hormone (FSH) content of the pituitary glands had not changed even after 4 days. Culture studies with pituitary cells from normal adult male and female rats for 4-7 days did not reveal a direct effect of synthetic LHRH or an agonist on PRL release. Chronic systemic administration of a LHRH agonist greatly inhibited the growth of the transplantable PRL-secreting rat pituitary tumor 7315a in female rats, while circulating PRL levels were also suppressed. However, no direct effect of the LHRH agonist was observed on PRL release from a tumor cell clone, derived from the 7315a tumor, and no LHRH-binding sites were detectable on the tumor.(ABSTRACT TRUNCATED AT 250 WORDS)

前立腺癌患者に対するLH-RH作動薬長期投与の精巣内分泌機能に及ぼす影響について

Six patients with advanced prostatic cancer who had been treated by long-term administration of LH-RH agonistic preparations (Buserelin or Leupron) were tested for their pituitary-testicular endocrine functions. Serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), prolactin (PRL), estradiol (E2) and dihydrotestosterone (DHT) were measured consecutively. In all medically castrated patients, serum levels of LH, FSH, T, DHT and E2 were suppressed and particularly serum T levels were below the castration level of 1.0 ng/ml. On the other hand, serum PRL levels were unchanged after the long-term treatment with the agonists. Serum LH and FSH levels failed to respond to LH-RH stimulation after the treatment, whereas serum T responded to stimulation by human chorionic gonadotropin (hCG) to various degrees. It was remarkable that, in 4 out of 6 medically castrated patients treated up to more than 3 years, serum T response levels above 1.0 ng/ml were noted. It is suggested that testicular endocrine function to secrete T and DHT in patients under treatment with long-term LH-RH agonist administration are still preserved in response to hCG stimulation.

20 EFFECTS OF PUBERTAL MATURATION AND LONG TERM EXPOSURE TO TRIPTORELIN ON FREE TSH ALPHA-SUBUNIT RELEASE IN FEMALE SUBJECTS

The release of the free TSH α-subunit (F-TSH-A) during TRH stimulation (200 μg IV/m2) was investigated in 8 prepubertal girls (4-9 years of age, group I), 8 girls with precocious puberty (4-8 years of age, pubertal stages 2-3, group II) and 12 menstruating women (group III). F-TSH-A was measured by a polyclonal RIA. Results were expressed as mean ± SEM (ng 1°-IRP-hCGα/ml). Basal values in group I, II, III were respectively 0.14 ± 0.02, 0.33 ± 0.08 (p = 0.02) and 0.47 ± 0.05 (not different from II). TRH peak values were respectively 0.59 ± 0.12, 0.75 ± 0.08, and 0.71 ± 0.06 (differences not significant). The increment between basal and peak values was significantly higher (p < 0.02) in group I (0.45 ± 0.07) than in group III (0.24 ± 0.03). Girls from group II were treated by IM injections every 4 weeks of the LH-RH agonist triptorelin (Decapeptyl microcapsules, 60 μg/kg body weight). After 6 months basal and peak levels increased respectively to 1.1 ± 0.12 and 2.0 ± 0.20 (p < 0.001 relative to pretreatment values). The increment (0.84 ± 0.11) was significantly higher than in groups I, untreated II and III. These data suggest that : 1-ovarian secretion might exert a suppressive effect on the release of F-TSH-A; 2-long term LH-RH agonist administration might increase α-subunit secretion not only by the gonadotroph cells, but also by the thyreotroph cells, provided a direct effect of TRH on the gonadotrophs can be precluded.

Serum inhibin levels in polycystic ovary syndrome: basal levels and response to luteinizing hormone-releasing hormone agonist and exogenous gonadotropin administration.

Serum inhibin levels were measured by RIA twice weekly for 4 weeks in 5 women with the polycystic ovary syndrome (PCOS). These were compared to those in 10 women with normal menstrual cycles. Serum inhibin levels were similar in the 5 PCOS women (mean, 199; range, 126-266 U/L) and were not significantly different from those in the normal women during the early follicular phase (227; 100-485 U/L) or midfollicular phase (243; 143-412 U/L) of their cycles. Inhibin levels were higher (P less than 0.001) in the late follicular phase (408; 227-732 U/L), at midcycle (623; 367-1058 U/L), and during the midluteal phase (1245; 898-1727 U/L) in the normal women compared to those in the PCOS group. Serum inhibin levels were also measured in PCOS (n = 8) and infertile (n = 14) women after the rise and subsequent diminished gonadotropin secretion that occurred during LHRH agonist administration. In both groups, serum LH and FSH increased after initiation of LHRH agonist administration; this increase was accompanied by parallel rises in serum estradiol and inhibin before suppression (PCOS women: r = 0.71; P less than 0.001; n = 108; infertile women: r = 0.42; P less than 0.05; n = 163). All hormone levels, including inhibin, decreased during continued LHRH administration. Five PCOS women underwent ovulation induction using combined LHRH agonist and human menopausal gonadotropin administration. Serum estradiol and inhibin rose in parallel in response to exogenous gonadotropins (r = 0.92; P less than 0.001; n = 77). In conclusion, we found no evidence of a primary defect in ovarian inhibin physiology in women with PCOS in terms of either basal or gonadotropin-stimulated (exogenous or endogenous) secretion.

Effect of gonadotropin secretion rate on the radiosensitivity of the rat luteinizing hormone-releasing hormone neuron and gonadotroph.

To test the hypothesis that the functional state of hypothalamic LHRH neurons and pituitary gonadotrophs might alter their radiosensitivity, we determined the experimental conditions under which the gonadotropin response to castration could be impaired by a single dose of cranial irradiation. Single doses of cranial irradiation greater than 2000 rads were lethal to unshielded rats. Shielding of the oropharynx and esophagus allowed the animals to survive doses up to 5000 rads. Doses between 2000 and 5000 rads had no effect on basal gonadotropin levels for as long as 3 months after irradiation. Irradiation caused a dose- and time-dependent impairment, however, in the gonadotropin response to castration. Impairment of the gonadotropin levels of castrate animals occurred in animals that were irradiated either before or after castration. However, rats irradiated in the castrate state showed a decreased susceptibility to irradiation damage. Additionally, stimulation of the pituitary by LHRH agonist (LHRHa) 3 h before irradiation significantly reduced the impairment of gonadotropin secretion 12-20 weeks after irradiation (P less than 0.05). Thus, increased functional activity of the rat hypothalamus or pituitary at the time of irradiation, induced by either castration or acute LHRHa administration, was associated with some protection against the gonadotropin-lowering effect of irradiation. Based upon these data, we hypothesize that stimulation of gonadotropin secretion at the time of therapeutic cranial irradiation in humans might protect against subsequent impairment of gonadotropin secretion.

D-Trp6-luteinizing hormone-releasing hormone inhibits sulpiride-induced hyperprolactinemia in normal men.

The effect of a potent agonistic analog of LHRH, D-Trp6-LHRH, on hyperprolactinemia induced by sulpiride was studied in normal men. Six men received sulpiride (100 mg, twice daily, orally) for 44 days. D-Trp6-LHRH was given sc during the last 2 weeks of sulpiride administration; the dose was 500 micrograms on the first day and 100 micrograms daily for the subsequent 14 days. All men had high serum PRL levels before D-Trp6-LHRH administration (mean +/- SEM, 56 +/- 9 ng/mL), which decreased significantly after the first dose of the analog (45 +/- 5 ng/mL; P = 0.031) and also after 15 days of analog administration (41 +/- 6 ng/mL; P = 0.016). These data demonstrate that administration of LHRH agonist can inhibit the hyperprolactinemic effect of sulpiride, suggesting a direct action of the analog on the pituitary gland to modulate PRL secretion.

Reversible inhibition of gonadal functions by a potent gonadotropin-releasing hormone agonist in adult dog

This study examines the recovery of spermatogenesis, testicular and plasma steroidogenesis and prostatic steroid content 26 weeks following cessation of daily treatment for 16 weeks with [D-Tryp 6]LHRH ethylamide (LHRH-A) in the adult dog. While administration of LHRH agonist resulted in testicular and prostatic weight reductions of 40–60%, a complete recovery is observed 26 weeks after cessation of treatment. The number of sperm in LHRH-A-treated dogs declined rapidly in the first 4 weeks, after which no ejaculation or erection is observed In these animals. Spermatogenesis completely recovered four months following cessation of treatment. While testicular steroidogenesis is completely inhibited during the treatment with the agonist peptide, normal levels of testicular steroids are observed with the exception of 17-hydroxypregnenolone, dehydroepiandrosterone and androst-5-ene-3β,17β-diol which are elevated above control levels and, furthermore, an accumulation of these Δ 5-steroids is also observed in the prostate after the end of treatment. Our data strongly suggest that chronic administration of an LHRH agonist may induce, after cessation of treatment, an overproduction of testicular steroids.

Adrenakche and growth during lhrh agonist (LHRH a) administration

Adrenakche and growth during lhrh agonist (LHRH a) administration

Interference in follicular maturation following acute intranasal lhrh agonist administration during the second week of the menstrual cycle

Interference in follicular maturation following acute intranasal lhrh agonist administration during the second week of the menstrual cycle

The effects of chronic administration of LH-RH agonists and antagonists on the menstrual cycle and endometrium of the rhesus monkey

Regularly cycling rhesus monkeys ( Macaca mulatta) were used to study the effects of prolonged administration of LH-RH analogs on the menstrual cycle and the endometrium. According to the treatment, animals were divided into: Group 1, vehicle; Group 2, LH-RH agonist (D-Trp 6 LH-RH, 20μg/ day); and Group 3, LH-RH antagonist ([N-Ac-D-Trp 1,3, D-p-Cl-Phe 2, D-Arg 6, D-Ala 10]-LH-RH, 200μg/day) for 90 days. Follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E 2) and progesterone (P) were measured every second day until thirty days past the discontinuation of drug administration. Endometrial biopsies were obtained on days 10, 40, 90 and 120 and processed for histologic exam and determination of estrogen (E) and progesterone receptors. Animals of Group 1 presented regular cycles, while those in Groups 2 and 3 remained anovulatory throughout the treatment. Animals of Group 2 presented different degrees of endometrial hyperplasia during treatment and animals of Group 3 showed either resting or atrophic endometrium. Administration of LH-RH agonist produced a marked increase in E and P endometrial receptors and the antagonist produced a decrease in P receptors. In both instances, reversal of the effects on the menstrual cycle and in the endometrium was observed 30 days after discontinuation of drug administration.

Testosterone supplementation attenuates the antifertility effects of an LHRH agonist in male rhesus monkeys.

Continuous administration of LHRH agonists in high doses disrupts pituitary and testicular function, thus providing an approach to male fertility control. However, testosterone supplementation is required to prevent the side effects associated with low androgen concentrations resulting from chronic LHRH agonist treatment. Three adult male rhesus monkeys were treated with the LHRH agonist, Buserelin, using osmotic minipumps implanted subcutaneously. Testosterone was administered simultaneously via Silastic capsules. This combined treatment led to a marked decrease in testicular volume, and all animals were oligospermic within 8-15 weeks of treatment. Azoospermia was, however, not achieved even after 22 weeks of treatment although in a previous study in which the LHRH agonist had been administered alone, azoospermia had been achieved after 8-10 weeks. It is concluded that in this primate species testosterone supplementation attenuates the suppressive effects of LHRH agonist infusion on spermatogenesis.

Changes in insulin binding in rat testis following testosterone and gonadotrophins administration.

Rat testis membranes possess insulin receptor whose autoregulation is different from conventional insulin target organs. In order to verify the importance of the functional activity of the Leydig cells, different approaches were selected to provoke a resting state of the cells and to measure insulin binding. Testosterone cypionate and LH-RH agonist administration, as well as hypophysectomy, led to a 50% decrease of insulin binding in testis while no effect or a slight increase was observed in hepatic membranes following hypophysectomy. HCG treatments restored insulin binding to its control levels in hypophysectomized animals. These modifications occurred without significant changes in insulin and glucose concentrations. It is concluded that pituitary LH is a key factor in controlling Leydig cell activity as well as its insulin receptor content.

Comparative effects of LHRH agonist and ovine LH administration on testicular steroidogenesis in intact adult rat

In order to better understand the effects of LHRH administration on testicular function in adult rat, we compared the inhibitory effects of LH and the LHRH analogue [D-Ser-(TBU) 6, des-Gly-NH 2 10]LHRH ethylamide upon testicular steroidogenesis and LH, FSH and prolactin receptor contents. Administration of LH as well as LHRH analogue resulted in a marked decrease of LH receptor levels, accompanied by a blockage at the level of 17-hydroxylase activity. We have been able to demonstrate that multiple LH administration can achieve a testicular desensitization comparable to that observed after LHRH agonist treatment.

Effects of chronic LHRH agonist treatment on the endometrium and ovaries of the stumptailed macaque

Eight stumptailed macaques were injected daily with 5 or 20 μg D-Ser(Bu t) 6des Gly luteinizing hormone releasing hormone ethylamide (LHRH agonist) for approximately one year in order to prevent ovulation. On the last day of treatment (7 monkeys) or during the mid-luteal phase of the first cycle after treatment (1 monkey), a laparotomy was performed. Uterine size was slightly smaller (P < 0.01) than in controls with normal cycles (n = 6). A full thickness wedge of anterior uterine wall was excised and examined histologically. Five of the agonist-treated monkeys had endometrium consistent with an atrophic or resting proliferative pattern, but in 2 the appearance varied from early prollferative to marked secretory. All appeared entirely benign. The remaining animal studied in the luteal phase after stopping treatment exhibited a normal secretory endometrium. Ovaries from 2 of the LHRH agonist-treated animals were also studied histologically and found to consist of follicles at various stages of maturation. The occurrence of endometrial activity in 2 of the 8 LHRH agonist-treated monkeys stresses the need for careful endometrial assessment during clinical trials involving repeated administration of LHRH agonists in women.

Stimulation of pituitary and testicular functions with LH-RH agonist or pulsatile LH-RH treatment in the rhesus monkey during the non-breeding season.

Out-of-season male rhesus monkeys were used to compare the effectiveness of pulsatile treatment with LH-RH and administration of LH-RH agonist on testicular function. Treatment with LH-RH agonist (1.0 microgram Hoe 766/day) for 11 weeks resulted in partial stimulation of pituitary and testicular functions. The pituitary LH response to the agonist increased during treatment. Testosterone levels were stimulated to within the normal range and 2 of the 4 treated monkeys produced ejaculates, but sperm counts were below normal. Pulsatile treatment with LH-RH (100 ng every 96 min for 7 days alternating with LH-RH agonist treatment for 7 days) in 2 monkeys induced full testicular activity after 7 weeks. Ejaculations were induced at a time when the rhesus monkey is normally sexually inactive. Seminal characteristics at the end of treatment were similar to values in the normal breeding season. In samples collected from one monkey over a 24-h period before treatment there were no LH spikes and very low testosterone levels. During pulsatile LH-RH treatment distinct LH and testosterone spikes occurred, comparable to those in the breeding season.

Similar luteinizing hormone-releasing hormone binding sites in rat anterior pituitary and ovary.

To study the luteinizing hormone-releasing hormone (LH-RH; luliberin) receptors in the rat anterior pituitary gland and ovary, 125I-labeled [D-Ser(TBU)6des-Gly-NH2(10)]LH-RH ethylamide was used as a labeled ligand. The binding characteristics were assessed by Scatchard analysis of labeled ligand binding and by potency displacement with unlabeled peptides. Similar Kd values, ranging from 0.1 to 0.3 nM, were found for the labeled and unlabeled peptides in both tissues. A similar order of potency was observed between the finding affinity of 15 peptides in anterior pituitary and ovarian homogenates and their biological activity on luteinizing hormone release in rat anterior pituitary cells in culture. These data demonstrate that the LH-RH receptors present in the rat ovary have a specificity similar to that of the anterior pituitary LH-RH receptor controlling secretion of luteinizing hormone and follicle-stimulating hormone. Moreover, the binding affinities of the LH-RH agonists and antagonists can account, at least up to a large extent, for their relative biological potencies. Although there definitely are specific LH-RH receptors in the ovary which may play a role in the antifertility effects observed after administration of LH-RH agonists, the possible physiological significance of these ovarian receptors is still unknown and of great biological interest.

Further Studies on the Inhibitory Effect of [D‐A1a6, des‐Gly‐NH210]LHRH Ethylamide on Spermatogenesis and Steroidogenesis in the Rat: Reversibility and Effect of Androgen Administration

Following the recent observation that chronic treatment with [D‐Ala6, des‐Gly‐NH210]LHRH ethylamide, a potent LHRH agonist, leads to an almost complete degeneration of seminiferous tubules in the rat, the time‐course of recovery of spermatogenesis after cessation of treatment was investigated. Adult rats injected with the LHRH agonist (100 ng, every second day) for four weeks were studied four, eight, and 16 weeks later. Although progressive improvement was noted from four to 16 weeks after cessation of treatment, about 25% of tubules still appeared completely degenerated at the end of the recuperation period. One month following cessation of treatment, testicular LH and prolactin receptor concentrations, testicular testosterone (T) and dihydrotestosterone (DHT) levels, and ventral prostate and seminal vesicle weights had returned to normal values. Testis weight, however, which was decreased by 40% one month after treatment with the LHRH analog, increased more slowly toward normal and was still at 85% of control value four months after treatment. Plasma LH and FSH levels, which were increased approximately 100% after treatment with the LHRH analogue, returned to within normal values between one and two months following cessation of treatment, respectively. Administration of androgens (T or DHT) concomitantly with the LHRH agonist only partially prevented the deleterious effects of the peptide on spermatogenesis. On the other hand, administration of the LHRH agonist had no effect on testicular morphology in hypophysectomized rats. These data show a rapid return to normal of the hypophyseal testicular elements responsible for androgen formation after desensitization by LHRH agonist treatment in adult rats. These results suggest that the inhibitory effect of chronic LHRH agonist administration on spermatogenesis is at least partially reversible, and that a decrease in androgen production is probably not the only factor involved in the inhibition of spermatogenesis by LHRH agonist treatment.