Estrogen 16 alpha-hydroxylase activity in human fetal tissues.

Estrogen 16 alpha-hydroxylase activity was measured in microsomes prepared from fetal tissues of first and second trimester human abortuses using [16 alpha-3H]estrone sulfate as substrate and NADPH as cofactor. Estrogen 16 alpha-hydroxylase activity was demonstrable in 13 of 14 fetal tissues examined in this study, viz. liver, adrenal fetal zone, adrenal neocortex, lung, kidney, intestine, heart, brain, skin, testis, spleen, pancreas, and stomach, and was either negligible or absent in placental tissue. The highest specific activity of the microsomal enzyme [pico-moles of product(s) formed per mg protein/h] was found in liver (mean +/- SEM, 338 +/- 62), and the next highest was found in the fetal zone of the adrenal cortex (70 +/- 20). The specific activities of estrogen 16 alpha-hydroxylase in adrenal neocortex, brain, skin, and testis were similar (25-53 pmol/mg protein X h) as were those in lung, kidney, intestine, heart, spleen and stomach (23-36 pmol/mg protein X h). The specific activity of the enzyme in the pancreas was 12 pmol/mg protein X h; the lowest specific activity, however, was in placental microsomes (0.2 +/- 0.1 pmol/mg protein X h).