ACTIVITIES OF AROMATASE AND 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA(4)-DELTA(5) ISOMERASE IN WHOLE-ORGAN CULTURES OF TISSUES FROM DEVELOPING ZEBRA FINCHES

The hormonal basis for masculine song development in the zebra finch r emains unidentified. To understand how steroids are differentially sup plied to the brains of males and females to cause sexually dimorphic d evelopment of this behavior, we have studied the steroidogenic capabil ity of zebra finch tissues during early development (1 to 8 days posth atching). Here, we report on the use of cultures of whole gonads, adre nals, and telencephalons to measure the activities of two steroidogeni c enzymes: aromatase, the enzyme that catalyzes the conversion of andr ogen to estrogen, and 3 beta-hydroxysteroid dehydrogenase/ Delta(4)-De lta(5) isomerase (3 beta-HSD), the enzyme that converts pregnenolone i nto progesterone. We also examined the effect of cAMP on aromatase act ivity in these tissues as this intracellular second messenger has been shown previously to regulate aromatase in both central and peripheral tissues of other species. In untreated cultures, aromatase was detect ed at the highest levels in male and female telencephalon and in ovary . Dibutyryl (dB)-cAMP had no significant effect on aromatase activity in any tissue. However, after dB-cAMP treatment, estrogens were regula rly detected in cultures of whole testes. Although this activity was r elatively low when compared to total activity found in other tissues, due to the small size of the testes at this age of development,,the sp ecific activity (per milligram of protein) might be high enough to pro duce some estrogen. Adrenal aromatase was unconfirmed in the presence or absence of cAMP. 3 beta-HSD activity was undetected in brain but wa s detected in gonads and adrenals from all birds. There were no signif icant differences in gonadal or adrenal 3 beta-HSD activity between ma les and females. Although these data present the first evidence for te sticular aromatase in the zebra finch, they provide no evidence to sup port a mechanism to generate a greater estrogenic signal in male zebra finches after hatching. (C) 1998 Academic Press.