The Relationship Between the In Vitro Activity of 3β-Hydroxysteroid Dehydrogenase Δ4–5-Isomerase in Human Sebaceous Glands and Their Secretory Activity In Vivo

3β-Hydroxysteroid dehydrogenase Δ4–5-isomerase (Δ5-3β-HSD) catalyzes an early step in the synthesis of testosterone from dehydroepiandrosterone (DHA). We compared enzyme activity in back skin biopsies with sebum excretion rate (SER) in 14 individuals. The rate of conversion of [7α-3H]DHA into [3H]-4-androstene-3,17- dione was measured in cryostat sections of skin and compared with the sebaceous gland content of the same biopsies. Reaction rate was proportional to the volume of sebaceous gland tissue in the sections. Enzyme activity was absent from sections without histologically identifiable sebaceous gland tissue. This suggests that the Δ5-3β-HSD is localized in sebaceous glands. SER, measured by a modified photometric technique at the biopsy site, correlated highly with sebaceous gland volume and with the rate of conversion of DHA into androstenedione in the biopsy. For each biopsy, specific activity of Δ5-3β-HSD in sebaceous glands was calculated by dividing the rate of formation of [3H]-4-androstene-3,17-dione by sebaceous gland volume. Specific activity of Δ5-3β-HSD did not correlate significantly with SER, suggesting that variations in concentration of Δ5-3β-HSD in sebaceous glands probably do not underlie variations in sebaceous gland activity