Adrenocortical function of the domestic fowl: effects of orchiectomy and androgen replacement.

The effect of orchiectomy and androgen replacement on cockerel adrenocortical function was investigated. Orchiectomized cockerels (2 weeks old) were implanted with Silastic tubing containing various amounts of one of the following steroids: cholesterol, testosterone (T), androstenedione (A4), and 5 alpha-dihydrotestosterone (DHT). Birds were administered additional implants, containing doses of steroids equivalent to those of the initial implants, at 4 and 8 weeks of treatment (i.e., 6 and 10 weeks of age). Sham-operated cockerels administered empty implants served as intact controls for comparison of data. Animals were killed after 10 weeks of treatment (12 weeks old). Trunk plasma corticosterone (B) and plasma T, and B production by collagenase-isolated adrenocortical cells incubated briefly (2 hr) with or without steroidogenic agents were measured by radioimmunoassay. Orchiectomy with implantation of the inert sterol, cholesterol (hereafter referred to as orchiectomy), did not alter plasma B concentrations and did not affect basal cellular B production or cellular B production induced by a maximal steroidogenic concentration of ACTH or that maximally supported by 25-hydroxycholesterol. However, orchiectomy did lower maximal 8-bromo-cyclic AMP-induced B production by 30%. Low-implant doses of A4 (1-cm implant) and T (0.3-cm implant), that maintained comb growth, lowered plasma B concentrations by 24-42%, whereas a high-implant dose of T (3-cm implant) and all implant doses of DHT had no effect on plasma B concentrations. Thus, androgen replacement had different effects on plasma B depending on the type of androgen and the implant dose. In contrast, androgen replacement consistently suppressed basal and maximal ACTH-induced cellular B production regardless of the type of androgen. Furthermore, the degree of suppression was dose-dependent. These results suggest that the differential effect of androgen replacement on plasma B concentrations was due to differences in the clearance of circulating B and/or differences in blood volume. In addition, the present study suggests that in the absence of the testes, androgens are suppressants of adrenocortical cell function in the domestic fowl.