Evidence that Pituitary 5α-Dihydrotestosterone Formation is Regulated through Changes in the Proportional Number and Size of the Gonadotrophic Cells

Abstract

³H-testosterone was incubated and its conversion to 5α-reduced metabolites measured in dispersed anterior pituitary cells before and after separation into fractions with different cell-type distribution by gradient sedimentation at unit gravity. In pituitary cells from 14-day-old female rats, 5α-dihydrotestosterone (DHT) formation (expressed per 10⁵ cells) was several times higher than in those from 14-day-old male and adult male rats. After unit gravity sedimentation the formation of DHT rose with the proportional number and size of gonadotrophs in the fractions of all animal groups studied. In a highly purified population of large gonadotrophs, prepared from 14-day-old females, DHT formation was 23 times higher than in a highly purified population of large somatotrophs, obtained from adult males. Isopicnic sedimentation in a metrizamide gradient partially separated the highly purified preparation of gonadotrophs from contaminating thyrotrophs. In the latter gradient DHT formation was low in the fraction enriched in thyrotrophs. When homologous gradient fractions from the three animal groups studied were compared, differences in DHT formation were of similar rank order of magnitude as differences in the proportional number of gonadotrophs in these fractions. The fractional distribution pattern was highly characteristic for each animal group. It is concluded that pituitary DHT formation occurs primarily in the gonadotrophs and that changes in overall 5α-reductase activity of the pituitary is based, at least in part, on changes in the distribution profile of number and size of the gonadotrophs.