Effect of long-term infusion of an LH-releasing hormone agonist on testicular function in bulls.

Continuous administration of LH-releasing hormone (LHRH) agonists is an effective method of suppressing testosterone secretion in the male. The effect of the LH-releasing hormone (LHRH) agonist, buserelin, administered to bulls by constant infusion from osmotic minipumps was studied. In one experiment with four treated and one control bull, 109 micrograms buserelin/day were administered for 22 days. Immediately after implantation, serum testosterone concentrations rose from below 35 nmol/l to 35-105 nmol/l, and all four buserelin-infused bulls showed increased testosterone secretion during the treatment period. After removal of the minipumps, testosterone concentrations decreased to pretreatment levels. In a second experiment bulls were infused for 42 days (four treated and one control), and identical results were obtained. Testosterone secretion was stimulated (52-87 nmol/l serum) during the entire treatment period. These results demonstrate that conditions for stimulation of the pituitary-testicular axis may vary between species. Infusion of low doses of LHRH-agonists in bulls has an extended stimulatory effect without immediate desensitization of gonadotrophin release.

Neurochemical effects of the synthetic ACTH4-9-analog Hoe 427 (Ebiratide) in rat brain.

The ACTH4-9-analog Hoe 427 systemically injected in a dose range from 0.01-10 micrograms/kg caused a fall in acetylcholine (ACh) content in different brain areas of the rat. This effect occurred 0.5 hour after a single administration and lasted up to 24 hours. The decrease in ACh content induced by Hoe 427 was more pronounced when the animals were pretreated with dexamethasone (over 7 days 1 mg/kg SC, daily). Coadministration of the choline uptake inhibitor hemicholinium-3 (HC-3) and Hoe 427 potentiated the decrease in ACh content induced by HC-3. In the same dose range Hoe 427 acutely evoked an increase of the activity of the enzyme choline acetyltransferase as well as an elevation of brain cyclic GMP content. These data indicate that Hoe 427 enhances ACh metabolism in rat brain after systemic administration.

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.

Treatment of cryptorchidism with pernasal gonadotropin-releasing hormone therapy.

Twenty-five boys between 1 and 10 years of age with unilateral or bilateral cryptorchidism were treated with 200 microgram of gonadotropin-releasing hormone (GnRH) pernasally six times daily until descensus was completed, or for 10 weeks at most. Complete descent of the tests occurred in 16 patients, usually after 2 to 5 weeks of treatment. No adverse side effects have been observed. Radioimmunologic measurements of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, and prolactin, carried out before treatment, at the end of treatment, and 6 months after treatment, showed a transitory increase of the LH responsiveness to GnRH in only four of the patients and in the group as a whole a slight but significant decrease of FSH responsiveness. There were no signs of precocious puberty. GnRH antibodies were not found.

Pharmacological studies on androgen suppression in therapy of prostate carcinoma.

In hormone-dependent prostate carcinoma, androgens can be suppressed into the castrate range by LHRH agonists. Testosterone secretion is blocked at two levels: testicular androgens and adrenal androgens. In humans, the contribution of testicular androgens is about 95%, whereas in the rat, the adrenal androgen secretion is negligible. Pharmacological studies were performed on the suppressive effect of the LHRH agonist, buserelin on androgen-dependent organs in adult rats. The reduction in pituitary and testicular binding capacity was monitored during treatment by injection, or by long-term infusion. Marked differences in suppressive mechanisms activated by the different regimens were observed. Changes in testicular steroid biosynthesis were analysed by incubation of testes after treatment with HCG, measuring the spectrum of C21/C19-steroids in incubation media. In particular, the levels of intraprostatic androgens were determined during treatment with daily buserelin injections, or with sustained release formulations of buserelin. The tissue content of testosterone and 5-alpha-dihydrotestosterone (DHT) were both markedly lowered. In castrate rats, stimulation of adrenal function by ACTH infusion had no effect on the prostate weight or intratesticular T/DHT content. Combination therapy during the initial phase of treatment by an androgen receptor blocker (cyproterone acetate) and buserelin (infusion or implants) was more effective to suppress prostate weight and intra-prostatic T/DHT content than therapy with the single compounds alone. Spermatogenesis and fertility were suppressed after prolonged treatment periods of 6-12 months; the testicular atrophy was not reversible in these long-term injection studies. Similar studies in dogs and monkeys have shown a different result: inhibition of spermatogenesis was fully reversible. It is concluded that studies on the mechanism of androgen suppression by LHRH agonists and the effects on androgen dependent organs provide useful information for the improvement in therapy of hormone-dependent prostate carcinoma.

The different mechanisms for suppression of pituitary and testicular function.

The differential mechanisms reducing androgen secretion by LHRH agonists are discussed with relevance to clinical therapy. LH secretion can be desensitised by exposure to agonists using high doses, frequent injections or sustained release/constant infusion. The desensitized pituitary is refractory to hypothalamic stimulation. Pituitary receptor suppression is associated with depletion of pituitary gonadotrophin content, and a decline of LH and FSH secretion to a basal rate. Recovery of LH responsiveness to endogenous LHRH stimulation requires restitution of gonadotrophin content (about 7 days in rats). After long-term infusions in normal men, testosterone secretion recovers within 7-10 days. The binding capacity of testicular LH/hCG receptors is reduced in rats after supraphysiological gonadotrophin stimulation, by agonists or directly by hCG, concomitantly the steroidogenic capacity of the testis in vitro is impaired. Qualitative changes in androgen biosynthesis are a marked fall in testosterone production and dose-dependent enhancement of progesterone production. After 12 months of buserelin injections, the changes in hCG-stimulated rat testes are an increased ratio of progesterone/17-OH-progesterone (inhibition of 17-hydroxylase), a reduced capacity for secretion of androstenedione and testosterone (block of 17,20-desmolase), and increased 5 alpha-pregnane-3,20-dione (this steroid inhibits the 17,20-desmolase, similarly to progesterone). After treatment, Leydig cell function recovers completely. Leydig cell hyperplasia is observed as a result of the steroidogenic changes. These findings in rats have not been observed in dogs, monkeys or in humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Antifertility effects of an LH-RH analogue in male rats and dogs.

The antifertility effects of a highly active LH-RH analogue, D-Ser(Bu)6-LH-RH(1-9)nonapeptide-ethylamide (buserelin) were studied in male rats and dogs. Pituitary-testicular function was not impaired by a "physiological" dose of 5 ng/rat; this dose gave reproducible LH release during chronic administration. At higher dose testicular LH receptors and responsiveness to HCG were diminished in intact prepubertal and adult rats. Pituitary inhibition was independent of gonadal or adrenal steroid feedback, and hypothalamic LH-RH as well as pituitary LH and FSH were reduced by 4 weeks treatment of castrate/adrenalectomized rats with 50 ng buserelin. In male dogs, a dose of 2.5 micrograms/kg sc reduced serum testosterone to 6% of controls within 8 weeks of treatment. Treatment was continued for 6 months and testicular involution was found to be reversible within 8 weeks of stopping treatment. LH-RH analogues at "supraphysiological" doses can be used as antifertility agents, but suppression of sexual activity in male dogs under treatment indicates that loss of libido will be a problem.

An implant of a gonadotropin releasing hormone agonist (buserelin) which suppresses ovarian function in the macaque for 3-5 months.

Four adult female stumptailed macaque monkeys with regular menstrual cycles and one with irregular cycles and dysfunctional uterine bleeding were treated with a single implant containing 2.6 mg of the GnRH agonist buserelin in a matrix of polylactide/glycolide copolymer (75:25). The implant was used as a cylindrical rod of 0.8 X 0.12 cm and implanted sc in the abdominal wall. The insertion of the implant was followed by a modest rise in serum concentrations of LH and FSH lasting 3-4 days before falling to basal values. The release profile of buserelin from the implant was measured in urine by a radioimmunoassay detecting the intact molecule and its major metabolites. Immunoreactive buserelin in urine was high between days 1-3 after implant after which there was a rapid decline to form a plateau between days 15-70 followed by a further gradual decline. This prolonged release of buserelin suppressed ovulation for a mean of 148 days (range 105-182 days) as indicated by absence of serum progesterone rises. Serum FSH concentrations were low for at least 75 days and during this time serum oestradiol concentrations were uniformly suppressed in all monkeys. Once the buserelin release from the implant declined serum FSH concentrations began to rise. There was a variable delay of 7-60 days before this rise in FSH was associated with stimulation of ovarian oestradiol secretion followed by rises in serum progesterone concentrations indicative of ovulation. Apart from the first menses after insertion of implant, 4 of the monkeys became amenorrhoeic for the period of anovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary and ovarian responses of post-partum acyclic beef cows to continuous long-term GnRH and GnRH agonist treatment.

Post-partum acyclic beef cows received continuous long-term treatment with GnRH (200 or 400 ng/kg body wt/h) or the GnRH agonist buserelin (5.5 or 11 ng/kg body wt/h) using s.c. osmotic minipumps which were designed to remain active for 28 days. All treatments increased circulating LH concentrations whereas FSH remained unchanged. Ovulation and corpus luteum (CL) formation as judged by progesterone concentrations greater than or equal to 1 ng/ml occurred in 0/5 control, 4/5 200 ng GnRH, 4/4 400 ng GnRH, 4/5 5.5 ng buserelin and 3/5 11 ng buserelin cows. The outstanding features of the progesterone profiles were the synchrony, both within and across groups, in values greater than or equal to 1 ng/ml around Day 6, and the fact that most CL were short-lived (4-6 days). Only 3 cows, one each from the 400 ng GnRH, 5.5 ng buserelin and 11 ng buserelin groups, showed evidence of extended CL function. Cows failed to show a second ovulation which was anticipated around Day 10 and this could have been due to insufficient FSH to stimulate early follicular development, or the absence of an endogenously driven LH surge. The highest LH concentrations for the respective groups were observed on Days 2 and 6 and by Day 10 LH was declining, although concentrations did remain higher than in controls up to Day 20.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory control of the pituitary LH secretion by LH-RH in male rats.

Luteinizing hormone-releasing hormone (LH-RH) was administered to prepubertal male rats (intact, castrate or castrate-adrenalectomized, 60 g body weight) for 28 days (1 microgram LH-RH/day, s.c.), at a 10-fold physiological dose, as compared to the minimal FSH-releasing dose of 100 ng/rat s.c. In intact rats, serum LH and weight of androgen-dependent organs (vented prostate, seminal vesicles) were reduced after 14 days of treatment. In castrate rats, the postcastration rise in serum LH was abolished by treatment. Pituitary LH content, FSH secretion and prolactin secretion were not suppressed. Hypothalamic LH-RH was increased at 14 and 21 days. In castrate adrenalectomized male rats, LH secretion was also suppressed by 1 microgram LH-RH s.c. x 28 days. The hypothalamic LH-RH content did not increase. The pituitary LH-RH receptor level was not down-regulated after 14 days treatment either in intact or castrate male rats. Pituitary inhibition (LH release) in rats by a supraphysiological dose of LH-RH given for 28 days indicates that the optimal regime for chronic treatment has to be determined by monitoring LH release at regular intervals. Direct pituitary inhibition by LH-RH may explain some of the unexpected antifertility effects observed with high doses of LH-RH.

Investigations of the carcinogenicity of the LH-RH analog buserelin (HOE 766) in rats using the subcutaneous route of administration.

A carcinogenicity study with the LH-RH analog buserelin (HOE 766) was conducted in male and female Wistar rats. The compound was administered subcutaneously daily for a period of 24 months to groups of 50 male and 50 female animals in doses of 0.0002, 0.0006, or 0.0018 mg/kg body wt, followed by a 6-month recovery period without any treatment. Male and female rats (100 each) received physiological saline and served as controls. The body weight development of all male rats was regular, but in females at all three dose levels significantly increased body weight gain in comparison to the control animals occurred. Food consumption was not affected in any group. No treatment-related changes in clinical signs and hematological parameters were noted. The chronic administration of HOE 766 did not influence the survival of the male rats while in females it was dose-dependently increased. Endocrinological examinations revealed decreased serum testosterone levels in males and reduced serum progesterone levels in females during the treatment period; the changes reverted to normal during the recovery period. Reduced weights of the testes and uteri as well as increased weights of the pituitaries and ovaries in females are compound-related. Histological examination of the animals which died intercurrently or were killed in extremis or at the end of the recovery period revealed irreversible and partly dose-dependent changes in testes and uterus, due to the pharmacodynamic properties of HOE 766, but gave no indication of any carcinogenic effect of the compound.