11-Ketotestosterone suppresses interrenal activity in rainbow trout (Oncorhynchus mykiss).

Interrenal activity in relation to sexual maturity in male rainbow trout, and the effects of in vivo treatment with 11-ketotestosterone (11-KT) were investigated. Silastic pellets containing either 11-KT or no steroid were implanted in maturing male and immature male and female rainbow trout for a total of 11 weeks. Two weeks before termination of the experiment, animals were subjected to crowding, and blood samples were taken 15-90 min after initial disturbance. At the termination of the experiment, head kidneys containing interrenal cells were removed and incubated in vitro with either human adrenocorticotropin 1-24 (ACTH) or with pregnenolone. 11-KT reduced the elevation of cortisol in response to confinement stress. Head kidney tissue of control and 11-KT-treated maturing males was significantly less responsive to ACTH and pregnenolone than tissue from immature males. Treatment of immature females with 11-KT similarly led to reductions in interrenal responsiveness. No difference in response was seen between tissue from control immature males and females. These data suggest that the attenuated stress response in maturing males is due, in part, to elevated 11-KT levels acting at one or more levels of the hypothalamus-pituitary-interrenal axis.