Serum gonadotrophins in rats after catration or heat treatment of the testes.

In rats spermatogenesis was disturbed by heat treatment of the testes. This resulted in increases of both LH and FSH. The increased gonadotrophin levels could be suppressed with testosterone. For suppression of FSH to levels of control animals more testosterone was needed than for LH. The increase of gonadotrophins after castration could be suppressed with testosterone released evenly from silastic capsules. For this suppression low serum levels of testosterone relative to testosterone levels in intact control animals were sufficient. This may indicate that testosterone episodically secreted has a lesser suppressive action on gonadotrophin secretion than a constant presence of this hormone. The suppressive action of testosterone on serum gonadotrophin levels after castration was potentiated by 1,4,6-androstatriene-3,17-dione, a steroid which inhibits strongly the enzymatic transformation of testosterone into oestradiol.