Hormonal effects of GnRH agonist in the human male: II. Testosterone enhances gonadotrophin suppression induced by GnRH agonist

Superactive analogues of gonadotrophin releasing hormone and testosterone, when administered together, synergistically inhibit gonadotrophin secretion and spermatogenesis in the rat. In order to determine whether testosterone also enhanced gonadotrophin suppression by GnRH agonist in the human male, two groups of four normal male volunteers first received either 10 or 100 micrograms of a GnRH agonist D(Nal2)6GnRH (GnRH-A) daily for 10 d. After at least a 50 d recovery period, the same subjects received a single injection of 200 mg of testosterone oenanthate (TE) on day 1 in addition to the same dose of GnRH-A daily for 10 d. Serum LH, FSH and testosterone (TS) concentrations were measured daily just prior to the next analogue dose, and on days 1 and 10 at 0, 1, 2, 4, 6, 8, 12, 16 and 24 h after the analogue injection. Daily administration of both 10 and 100 micrograms of GnRH-A alone resulted in an early phase of stimulation followed by progressive decline in LH, FSH and testosterone to levels below baseline by day 10 despite continued administration of GnRH-A. Addition of testosterone to 10 micrograms of GnRH-A resulted in hormonal responses identical to those seen with GnRH-A alone. Combined treatment of testosterone with 100 micrograms of GnRH-A did not blunt the peak LH and FSH responses on day 2, but resulted in significantly lower LH (mean integrated responses: 187 +/- 30 vs. 234 +/- 42 mIU-d/ml) and FSH (mean integrated responses: 20.6 +/- 3.3 vs. 32.8 +/- 4.2 mIU-d/ml) responses from days 3 to 11. By day 11, all subjects receiving combined treatment (GnRH-A 100 micrograms + testosterone oenanthate) had undetectable serum FSH levels. In contrast, serum FSH concentrations on day 11 after treatment with GnRH-A alone were 43.6 +/- 8.9% of control and none of the subjects had values below the limit of detection. Serum testosterone levels in the combined treatment group did not fall below baseline by day 10 in either the 10 (161.4 +/- 48%) or the 100 micrograms GnRH-A groups (104.6 +/- 11.2%), while in the group receiving GnRH-A alone, testosterone levels declined to 45.6 +/- 8.3% and 80 +/- 18.8% with the 10 and 100 micrograms dose respectively. We conclude that addition of a suppressive dose of testosterone to an appropriate dose of GnRN-A significantly enhances gonadotrophin suppression by GnRH-A in the human male.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of an LHRH agonist analog upon sexual function in male dogs. Suppression, reversibility, and effect of testosterone replacement

Male beagle dogs were injected once daily with 10 micrograms/kg of [6-D-(2-naphthyl)alanine]-LHRH (D-Nal(2)6-LHRH), a potent LHRH agonist, for periods up to 42 days, with recovery periods up to 172 days. Blood samples collected at regular intervals were assayed for LH, FSH, and testosterone; total ejaculates were collected and analyzed weekly, and animals were sacrificed at various intervals for sex organ weights and histology. The first injection of D-Nal(2)6-LHRH caused an acute elevation in plasma levels of LH, FSH, and testosterone, measured at 2 and 4 hours after the injection. This acute response to injection was attenuated with each successive injection and by two weeks no elevation was seen, suggesting a down-regulation of pituitary response. Basal levels of LH and testosterone were maximally depressed by four days of treatment. Testis volume, duration of erection, ejaculate volume, sperm count, sperm motility and testis volume all declined during treatment, with sperm count significantly lowered by two weeks and ejaculation volume becoming zero by five weeks of treatment. Spermatogenesis, assessed histologically, was partially suppressed at ten days and completely suppressed by 38 days of treatment. All parameters returned to normal following cessation of treatment. Recovery time was longer for the dogs treated for 42 days than for those treated for ten days. When testosterone was supplemented during 42 days of agonist treatment, basal plasma testosterone levels were maintained at the low end of the normal range. Testosterone supplementation did not prevent pituitary down-regulation, suppression of spermatogenesis, or the decrease in testis and epididymis weights, but prevented the decline in duration of erection. Ejaculate volume and sperm count declined more slowly with combination treatment than with agonist alone. During the decline in sperm count sperm motility was maintained with combination treatment. Injection of hCG into control and agonist treated dogs resulted in similar percentage increases in plasma levels of testosterone, although peak levels were greater in control than in treated animals. The data suggest a pituitary desensitization with this LHRH agonist in the dog but only a minor role for testicular desensitization.

Inability of continuous long-term administration of D-Nal(2)6-LHRH to abolish fertility in male rats

A highly potent agonist of LHRH, [6-D-(2-naphthyl)-alanine]-LHRH, was administered chronically for 12 weeks to adult male rats by repetitive implantation of pellets, and its effects upon mating, fertility, and reproductive organ weights have been evaluated. Although significant declines in testicular (P less than 0.001) and epididymidal (P less than 0.001) weights were achieved, no effects on seminal vesicles, prostate, or pituitary weights were observed. After 12 weeks of continuous treatment, three of six agonist-treated rats were still successfully impregnating females. The decline in successful impregnation appeared to be related to the observed reduction in testicular spermatogenesis and in numbers of epididymal spermatozoa. The drug effects appeared reversible, as all six of the agonist-treated rats were fertile by the fifth week after cessation of treatment. Plasma levels of testosterone were markedly elevated immediately after implantation of each pellet and consistently, but not significantly, lowered during the inter-implantation periods. These observations, and the lack of effect on accessory organ weights, are consistent with the maintenance of libido in these treated rats. This is the second demonstration of a selective inhibition of spermatogenesis in the absence of a marked decline in gonadal steroidogenesis with this agent. As in the first demonstration using twice weekly injections, the degree of inhibition of spermatogenesis was insufficient to abolish fertility in the treated male rats.

Suppression of luteal and placental function in pregnant baboons with agonist analogs of luteinizing hormone-releasing hormones

Implantation of pelleted agonistic analogs of luteinizing hormone-releasing hormone (LH-RH) into six pregnant baboons, ranging between 14 and 21 days after mating in individual animals, resulted in two abortions: one at 39 and the other at 67 days after mating. Plasma progesterone levels were low in treated animals through the 23rd day after mating, in spite of rising levels of plasma chorionic gonadotropin. Plasma levels of progesterone then rose rapidly to normal in five of six animals. Plasma estradiol levels were low from treatment on in the late-aborting animal but were normal until 5 days before delivery in the early abortant. The profile of circulating chorionic gonadotropin was truncated in treated animals, which may be the first indication of a paradoxical effect of LH-RH agonist on the trophoblast.

Endocrine and behavioral effects of continuous exposure of male rats to a potent luteinizing hormone-releasing hormone (LHRH) agonist: evidence for central nervous system actions of LHRH

Continuous exposure of intact male rats to [6-D-(2-naphthyl)-alanine]LHRH, a highly potent LHRH agonist, diminished testis and pituitary weights and decreased basal plasma levels of testosterone and LH. In addition, treatment with this analog abolished the pituitary hypertrophy and LH hypersecretion normally associated with castration. Alterations of male sex behavior were also noted in these animals. Analog-treated intact rats showed longer intromission latencies and mount latencies in early tests and ceased to show sexual behavior 6-8 weeks after initiation of treatment. In addition, the gradual decline in behavior normally observed after castration was markedly accelerated by analog administration. Castrates bearing 5-mm Silastic testosterone-containing capsules which maintained copulatory performance displayed behavioral deficiencies when given the peptide. No significant effect of analog was noted in rats with 30-mm Silastic implants, which provide a higher level of testosterone replacement. Continuous analog treatment promotes endocrine effects consistent with complete antagonism of the effects of endogenous LHRH. The behavioral disruption associated with this manipulation suggests a role for endogenous LHRH in maintaining sex behavior in a low testosterone environment.