Multihormonal Control of Microsomal 5α-Reductase Activity in Cultured Adult Female Rat Hepatocytes*

The activity of microsomal 5α-reductase, active on 3-oxo-4-ene-steroids, is much higher in adult female than in adult male rat liver. To examine the hormonal control of this enzyme under defined in vitro conditions, adult female rat hepatocytes were isolated by collagenase perfusion and cultured onto collagen membranes. The isolated hepatocytes form a nonreplicating monolayer after 24 h when cultured with or without serum, although the addition of fetal calf serum (FCS) or charcoal-extracted FCS improves hepatocyte plating efficiency. The charcoal-extracted FCS also significantly increases the 5α-reductase activity in cells cultured for 48 h. Time-course studies on 5α-reductase activity in isolated cells show that the activity in isolated cells is significantly lower than that in the intact animal. The activity is stable for 48 h in culture and then decreases. In cells cultured for 48 h, insulin significantly increases 5α-reductase activity at all doses tested (0.005–50 μg/ml), whereas estradiol induces hepatic 5α-reductase activity only at the highest dose (10-5M). The direct effect of pituitary hormones on microsomal 5α-reductase activity was evaluated by culturing adult female rat hepatocytes with rat PRL (rPRL-NIAMDD B-2), rat GH (rGH-NIAMDD B-6), PRL plus GH, or a crude adult female rat pituitary extract. The pituitary extract had a biphasic effect on reductase activity, i.e. activity was increased at the 0.1 mg/ml dose and decreased at higher doses (1 and 5 mg/ml). 5α-Reductase activity was not increased by either PRL (0.02–20 μg/ml) or PRL plus GH (0.02–2 μg/ml of each), but GH (0.02–20 μg/ml) caused a dose-dependent increase in 5α-reductase activity. The activity was not significantly changed at the lowest dose of GH, but at the highest dose the increase was significantly greater than at all other doses. Neither dexamethasone nor T3 in combination with GH modified the activity of 5α-reductase observed with GH alone, but an increase was observed with the combination of GH and estradiol. These results support the concept of GH as the most prominent pituitary hormone involved in regulating 5α-reductase activity.