Testosterone 5 alpha-reductase activity of skin fibroblasts. Increase with serial subcultures

Cultures of skin fibroblasts from different anatomical sites have been established and testosterone 5 alpha-reductase assayed after the 2nd, 6th and 12th subcultures. After the 2nd passage, 5 alpha-reduction of testosterone to both dihydrotestosterone and androstanediols correlated well with that measured in direct assays performed in total skin homogenates; this is an additional evidence that different types of skin have specific levels of testosterone 5 alpha-reductase activity. However, there was a marked increase in 5 alpha-reductase activity with successive subcultures (X4--5 between 2nd and 12th subcultures) in all the cell strains studied. This finding could explain why data concerning 5 alpha-reductase in cultured skin fibroblasts are often conflicting with those in skin homogenates. It emphasizes the necessity of performing enzyme assays after the same number of passages to allow comparison from strain to strain. Different hypotheses are discussed in order to explain such variations of 5 alpha-reductase in cultured human skin fibroblasts.