5-BETA-REDUCTASE AND OTHER ANDROGEN-METABOLIZING ENZYMES IN PRIMARY CULTURES OF DEVELOPING ZEBRA FINCH TELENCEPHALON

Enzymes in the avian brain irreversibly catalyze the conversion of and rogens into either active metabolites (aromatase and 5 alpha-reductase ) or inactive metabolites (5 beta-reductase). 5 beta-reductase is thou ght to influence the formation of active metabolites by reducing the c oncentration of androgenic substrate available for these reactions. Ho wever, because these enzymes have different regional, cellular and sub cellular distributions in brain, the traditional method to measure enz yme activity in brain homogenates may be inaccurate because of artific ial mixing of enzymes. Recently, we have prepared primary cell culture s from the telencephalons of developing zebra finches. Cell cultures o ffer the advantage that enzyme activity can be measured in live cells in which the relative distribution of enzymes may more closely reflect that found in vivo. We have previously reported that aromatase is exp ressed at high levels in these cultures, and that it is active in both neurons and in glia, Here we report on the activities of 5 alpha- and 5 beta-reductase in these cell cultures, Along with aromatase, 5 beta -reductase was expressed at high levels in these mixed cell cultures, including cultures highly enriched in glia. This suggests that 5 beta- reductase is present in non-neuronal cells in brain, possibly cc-local ized with aromatase, However, despite the presence of 5 beta-reductase , aromatase was detected reliably in vitro even when the concentration of substrate was low. Thus, 5 beta-reductase does not prevent the syn thesis of estrogen in the telencephalon of developing zebra finches. B y contrast, 5 alpha-reductase activity was very low or absent in these cultures. Thus, cells expressing 5 alpha-reductase may be poorly repr esented in these cultures. Alternatively, 5 beta-reductase and aromata se together may interfere with the synthesis of 5 alpha-reduced androg ens in the zebra finch telencephalon.