The effect of gonadectomy on the response of the pituitary I.C.S.H.-content to steroid sex hormones. I. The effect of steroid sex hormones on the pituitary I.C.S.H.-content of rats gonadectomized shortly before the beginning of treatment.

Abstract

ABSTRACT The effect of chronic administration of sex hormones on the pituitary I. C. S. H.-content was studied in intact and gonadectomized rats. If the treatment of gonadectomized animals was not started until a considerable time had elapsed after the operation, the resulting decrease in the pituitary I. C. S. H.-content was less than expected on the basis of dose and duration of treatment. The hypothesis was investigated whether this is due to gradually evolving changes in the hypothalamo-hypophyseal system, initiated and caused by gonadectomy. In accordance with this conception, treatment of spayed female rats with high doses of oestradiol benzoate and testosterone propionate from the day after the operation onwards caused a fall in the pituitary I. C. S. H.-content to the same final level as was reached in intact control animals after treatment with these doses. However, if lower doses of oestradiol benzoate and testosterone propionate were given, there still remained a difference between intact and gonadectomized rats: again, the decrease in the pituitary I. C. S. H.-content was less in gonadectomized than in intact animals. There are two possibilities: a) in rats, testosterone propionate and oestradiol benzoate are not the physiological hormones responsible for the pituitary inhibition; b) castration induces rapid changes (e. g. by way of a reflex) in the hypothalamo-hypophyseal system, which increases the resistance to the influence of steroid sex hormones. The latter hypothesis which, according to available evidence, seems the more probable, will be discussed in a following paper.