IN VITRO PROGESTERONE METABOLISM BY RAT TESTICULAR TISSUE AT DIFFERENT STAGES OF DEVELOPMENT

Abstract

ABSTRACT A systematic study of progesterone metabolism in incubates of testicular tissue from rats 1 to 120 days of age was conducted. Progesterone was avidly metabolized, regardless of the age of the animal. While striking age-dependent changes in the pattern of conversion of progesterone to androgens were observed, small amounts of 17α-hydroxyprogesterone and 17β-oestradiol were formed in all incubates, regardless of age of the animal. In newborn rats the major metabolites of progesterone were testosterone (44% conversion) and androstenedione (5% conversion). Formation of these two compounds gradually diminished with age until only small amounts were formed in tissue from 20-day old rats. From this nadir, conversion to testosterone started to increase at the age of 40 days, and reached constant adult fevels by 90 days; androstenedione started to increase at 30 days. Conversely, 5α-reduced androgens, androsterone, 5α-androstanediol and isoandrosterone, were barely detectable in testicular tissue of newborn rats, gradually increased to a peak by age 20–30 days, and then declined to barely detectable levels by age 90 days and older. These findings demonstrate that testicular tissue of postnatal rats of all ages contain enzymes involved in the biosynthetic pathways from progesterone to androgens, as well as aromatizing enzymes. The physiologic significance of 5α-reductase activity during differentiation of the androgen biosynthetic pathways remains to be determined.