Effects of treatment of neonatal rats with highly purified FSH alone and in combination with LH on testicular function and endogenous hormone levels at various ages

Abstract

ABSTRACT Factors which play a role in the regulation of testicular size in rats were investigated using neonatal animals treated with exogenous gonadotrophins for 2 or 3 weeks, starting on the day after birth. Effects on testis weight and various aspects of the pituitary-testicular axis were evaluated up to the age of 9 weeks. Daily treatment with human FSH (Metrodin; 0·15 U/g body wt) for 2 or 3 weeks, starting on the first day or 1 week after birth, resulted in enlargement of the testes, increased testicular content of inhibin and a suppression of pituitary and plasma FSH. The relative increase of testis weight decreased after cessation of treatment. Injections of human FSH combined with administration of human LH (Pergonal) for 3 weeks, starting on the first day after birth, resulted in larger testes immediately after treatment. In addition, an increased amount of interstitial tissue was observed in these animals. Pituitary and plasma FSH and LH were suppressed after this treatment, while the growth of the accessory sex organs was significantly stimulated. In animals treated with human FSH during the first 2 or 3 weeks of life, levels of rat FSH in blood samples collected at weekly intervals were significantly suppressed until the animals were killed at the age of 9 weeks. In the animals treated with human FSH and human LH, both FSH and testosterone concentrations were significantly lower than those in control animals between the ages of 4 and 9 weeks. At the age of 9 weeks testicular weights were still higher than those in control animals after these treatments. In the treated animals, no histological abnormalities of spermatogenesis were observed. We conclude that the first 3 weeks after birth are important for the establishment of testis size in the rat because during this period it is possible to stimulate mitoses of Sertoli cells with FSH. To obtain a permanent increase in testis size a longer period of treatment with exogenous gonadotrophins is needed. A possible feedback suppression of endogenous gonadotrophins by inhibin in FSH-treated rats and by inhibin and testosterone in the FSH- and LH-treated 3-week-old animals could be the reason for the relative delay of testicular development after the end of the treatments. The low endogenous level of LH which was observed caused impaired Leydig cell function in animals which were treated with FSH and LH. J. Endocr. (1988) 116, 413–420