Aromatase activity in cultured human genital skin fibroblasts.

Aromatase activity of human genital skin fibroblasts grown in cell culture was studied using both [1,2,6,7-3H] androstenedione (A) and [1-3H]A as substrates. With the former substrate the generation of [3H]estrogens was determined, whereas with the latter substrate, the formation of [3H]H2O was measured. Our results showed that the release of [3H]H2O from [1-3H]A provides an accurate and sensitive method for determining aromatase activity in cultured human skin fibroblasts. Because genital skin fibroblasts also possess marked 5 alpha-reductase activity, we found that addition of an alternate substrate for 5 alpha-reductase was necessary to prevent shunting of A from the aromatase pathway. Hence, all aromatase assays were carried out in the presence of 5 microM progesterone. Under these experimental conditions, no correlation was found between levels of 5 alpha-reductase and aromatase activities. The Michaelis-Menten constant (Km) of the aromatase in cultured genital skin fibroblasts measured in the presence of A and added progesterone ranged between 10 and 39 nM, and the maximum velocity (Vmax) ranged between 0.14 and 1.46 pmol product/mg protein/h. These values are in good agreement with those previously described for adipose tissue stromal-vascular cells, suggesting that the aromatase complexes are similar in skin and adipose tissue. We conclude that skin may be an important site for aromatization of androgens to estrogens in men.