The concentrations of LH and FSH were measured in the blood and adenohypophyses of castrated male rats exposed to high levels of testosterone propionate for 1 to 18 weeks. In intact male and female rats, similarly treated for 1 to 5 weeks, blood levels could not be measured but pituitary hormone levels were. Histological study of the pituitary gonadotrophic cells of all groups revealed a striking correlation between their regression, in response to androgen treatment, and the decline in pituitary LH stores. No light-microscopic correlate of the marked, progressive increase in pituitary FSH concentration was detected. Thus, when the pituitary FSH:LH ratio had increased 90 fold, all gonadotrophs appeared inactive.

Although these studies failed to reveal the specific cellular source(s) of FSH and LH, they did clarify several aspects of the dynamics of the pituitary secretory responses to orchidectomy and androgen treatment. In the light of this information, the suggestion is made that the greatest dichotomy between pituitary FSH and LH stores is not coincident with — and probably occurs later than — that between LH and FSH secretion. Such asynchrony between the various phases of the FSH and LH secretory responses to these treatments (castration and/or androgen administration), may explain several seeming discrepancies among earlier reports on this subject.