Chronic toxicity and reversibility of antifertility effect of immunization against gonadotropin-releasing hormone in male rats and rabbits.

The chronic systemic toxicity of immunization with gonadotropin-releasing hormone, conjugated to tetanus toxoid (GnRH-TT), was investigated in male rats and rabbits in order to start Phase I clinical trials. Groups of rats and rabbits were immunized with GnRH-TT dissolved in aqueous adjuvant. The antigen was administered at weeks 0, 4, and 8, followed by boosters to maintain high antibody titers. At termination (8-9 months after first immunization), twenty rats and ten rabbits exhibiting the highest mean anti-GnRH titers and all the controls were selected for complete toxicological evaluation. In the rat study, a castrated control group was included for comparison with the immunized group. The hematological and serum chemistry parameters of immunized rats and rabbits were not affected in a significant manner. Most of the changes in serum chemistry of immunized rats were also found in castrated rats, indicating that the changes are most likely due to the withdrawal of androgenic support. The weights of the testes, epididymides, and sex accessory glands were lower in all immunized animals. There was significant atrophy of the germinal epithelium, which, however, sustained a population of Sertoli cells, spermatogonia, and pachytene spermatocytes. Other morphological changes in the prostate, seminal vesicles, pituitary, and mammary gland reflected the effect of androgen withdrawal. The decrease in the weight of liver, kidney, and heart seen in the immunized rats was also present in castrated rats and was not associated with any histopathological changes. The reversibility of immunization-induced infertility was investigated by mating the rats with normal females. Four months after the start of immunization, 9 out of 10 immunized rats were infertile whereas by nine months, all rats had regained fertility. Thus, it is concluded that immunization with GnRH-TT had no systemic toxicological effects in the adult male rats and rabbits for the period studied. The results also indicated that the GnRH-TT immunization had an antifertility effect in male rats. Fertility was restored following cessation of immunization and decline in anti-GnRH antibody titers.

A 90-day subcutaneous toxicity and fertility study of a LHRH antagonist in rats.

[Ac-D2Nal1,4Cl-DPhe2,D3Pal3,Arg5,DGlu6+ ++ (anisole adduct),DAla10]-GnRH (Nal-Glu) is an antagonist of LHRH and has the potential to be utilized as an antigonadal agent. A study was undertaken to evaluate the toxicological effects of Nal-Glu in rats. Nal-Glu, dissolved in 5% mannitol in water containing 9 ml/liter benzyl alcohol, was administered subcutaneously. In subchronic studies, groups of 12 male and 12 female rats received 0, 50, 250, or 1250 micrograms/kg body weight (BW) Nal-Glu for 90 days and were killed on Day 91. Additional groups of male and female rats were given the high dose of Nal-Glu (1250 micrograms/kg BW) or vehicle for either 30 or 90 days. Their fertility was assessed by mating them with normal animals. Unlike some other LHRH antagonists, Nal-Glu exhibited a low potency for causing in vitro histamine release from rat peritoneal mast cells. Furthermore, in acute in vivo studies, Nal-Glu was less active in the induction of peripheral edema. In the subchronic study, all doses of Nal-Glu were well tolerated and there were no apparent systemic toxic effects. The pharmacological effects of Nal-Glu were quite evident, however. Nal-Glu treatment led to a significantly decreased body weight gain in the males and a significantly increased body weight gain in the females. There was a dose-dependent decrease in weights of gonads and reproductive organs in both the sexes. Some of the hematological and serological parameters were significantly different in Nal-Glu-treated animals. However, most of the values were within the normal range and are considered to be of no toxicological significance. Histopathological evaluations were made in the control and high-dose groups only. In the male, a seminiferous tubular degeneration and atrophy of the interstitial cells was seen. The prostate and seminal vesicles were also atrophied and the epididymides were devoid of spermatozoa. In the females, the ovaries and uteri were atrophic. The injection site of Nal-Glu-treated rats had inflammatory changes indicative of a local irritating action of the drug. All other tissues had normal histomorphology. Both male and female rats became infertile when 1250 micrograms/kg Nal-Glu was administered for 30 days. Normal fertility was restored 8 weeks after cessation of 90-day treatment. It is concluded that repeated administration of Nal-Glu leads to reversible infertility in both male and female rats. Although it was irritating at the site of injection. Nal-Glu had no systemic toxicological effects.