Androstenedione metabolizing enzymes present in guinea-pig peritoneal macrophages were investigated using tritium-labeled androstenedionc as the substrate. We found that the metabolites of [3H]-androstenedione produced by these macrophages were testosterone. 5α-androstane-3,17-dione, isoandrosterone, androsterone, 5α-dihydrotestosterone, 5α-androstane-3α,17β-diol and 5α-androstane-3β,17β-diol. The rates of metabolite formation remained linear as a function of time of incubation for approximately 30 min and with macrophage number up to 2 × 107 cells per ml. The formation of these metabolites is indicative that the following androstcnedione metabolizing enzymes are present in guinea-pig peritoneal macrophages: 5α-reductase, 3α-hydroxystcroid oxidoreductasc, 3β-hydroxysteroid oxidoreductase and 17β-hydroxystcroid oxidoreductasc. It is possible, therefore, that the macrophage, in vivo. may play a role in the metabolism of blood-borne androstcnedione to potent androgens. These hormones are important in the regulation of many biological processes, possibly including the activity of the macrophage itself.
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