ALTERED BRAIN METABOLISM OF TESTOSTERONE IS CORRELATED WITH REPRODUCTIVE DECLINE IN AGING QUAIL

An increasing proportion of aging quail males shows no sexual behavior. A decrease in the mean size of the testes, cloacal gland and sternotracheal muscles is observed. In both sexually active and inactive males plasma testosterone decreases with age but more so in inactive birds. The behavioral and morphological changes observed during aging are correlated with shifts in the intracellular testosterone metabolism resulting in a change in the ratio of active vs. inactive metabolites. In the hypothalamus there is a steady decrease with age of 5.beta.-reductase activity in all birds and an increase in 5.alpha.-reductase activity only in the birds which remain sexually active. In the cloacal gland the 5.beta.-reductase activity markedly increases with age but more so in the birds which become sexually inactive. The effects of testosterone may be controlled by enzymatic shifts which could modulate the sensitivity to the hormone at the cellular level.