In fibroblasts derived from human adipose tissue, aromatase induction is observed after exposure to 1 microM cortisol in the presence of serum or platelet-derived growth factor (PDGF). Progesterone suppresses this induction in a dose-dependent manner, 10 microM resulting in complete inhibition. A reduced cortisol concentration (0.1 microM) concomitantly reduces the progesterone concentration required for effective inhibition (10-100 nM). This effect of progesterone is specific, as neither the release of cellular enzymes nor aromatase induction by dibutyryl-cAMP, which acts independently from cortisol, are affected. However, the inhibitory effect of progesterone requires its presence throughout the induction period. Kinetic studies in intact cells reveal a reduced number of aromatase active sites upon progesterone treatment, whereas progesterone at near-physiological concentration (100 nM) does not inhibit aromatase activity in isolated microsomes. Semi-quantitative reverse transcriptase PCR analysis shows reduced amounts of aromatase mRNA in progesterone-treated cells, indicating specific inhibition of the glucocorticoid-dependent pathway of aromatase induction. The inhibitory effect of progesterone is not blocked by the anti-progestin ZK114043, excluding action via progesterone receptors and indicating competition for the glucocorticoid receptor. Progesterone must be considered a potential physiological inhibitor of glucocorticoid-dependent aromatase induction in adipose tissue. It is proposed that it is a suppressor of aromatase induction in adipose tissue in premenopausal women.

Dehydroepiandrosterone (DHEA) is a ubiquitous adrenal hormone with immunomodulatory effects such as inhibition of the production of monokines. Whether DHEA itself or the downstream steroids are the immunomodulatory effector hormones in target cells is not known. In this study, we investigated the conversion of DHEA to downstream steroid hormones in target macrophages. Within 1 day of culture with radiolabeled DHEA, monocyte-derived macrophages converted DHEA to significant amounts of Delta5-derivatives such as 16OH-DHEA, 3beta, 17beta-androstenediol (A'diol), and 3beta,16alpha, 17beta-androstenetriol (A'triol). However, the production of Delta4-steroids (androstenedione (A'dione), testosterone (T), and 16OH-T) and estrogens (estrone, estradiol, and estriol) was relatively low. Further cultivation of macrophages for 5 days with radiolabeled DHEA resulted in a significant (P<0.05) increase of the molar amounts of A'triol (P=0.012), 16OH-T (P=0.008), and estriol (P=0.003). In contrast to monocyte-derived macrophages, monocytes did not express aromatase mRNA, which was demonstrated by RT-PCR (P<0.01). Furthermore, DHEA in macrophages significantly inhibited one of the downstream converting enzymes, the aromatase, which was not demonstrated in the presence of the typical macrophage activator, lipopolysaccharide (LPS) (P<0.01). In conclusion, conversion of DHEA to physiologically relevant amounts of Delta5- and Delta4-steroids and estrogens was demonstrated in monocyte-derived macrophages. The conversion depends on maturation of monocytes and local factors such as the presence of LPS. The conversion of DHEA leads to an increase of downstream effector hormones in target macrophages which may be an important factor for local immunomodulation.