Abstract
Since estrogen and androgen receptors are found in osteoblastic cells, a direct effect of sex steroids on cell growth and proliferation in osteoblasts is suggested. Although the existence of sex steroid converting enzymes in osteoblastic cells have been reported, estrogen and androgen function on osteoblasts is not clear yet. To determine androgen metabolism in osteoblastic cells, the following in vitro incubation study was carried out. Cell free homogenate of a rat osteoblast cell line, UMR106-01 and C26, were incubated with [4-14C] -Testosterone (T), [4-14C] -Androstenedione (A) . In UMR106-01, formation of dihydrotestosrerone (DHT), 5α -and rostanedione (5α-A) from the corresponding substrate was identified by crystallization to constant specific activity. Michaelis constant (Km) for T was estimated as 42μM. In C26, T was identified from A, and Km was estimated as 41μM. The expressions of 5α -reductase type I messenger ribonucleic acid (mRNA) in UMR106-01 and 17 β-Hydroxysteroid dehydrogenase (17 β-HSD) type I in C26 were demonstrated by a reverse transcription-polymerase chain reaction. Formation of DHT from T and 5α -androstanedione from A and were found in UMR106-01, and T formation from A was found in C26. These results demonstrating the enzyme activity of 5α -reductase and 17 β -HSD suggested the capacity of osteoblasts to convert androgen to active forms. In addition, these results indicate that local metabolism of androgens in osteoblastic cells may play an important role on bone metabolism.
