Enhancement of Follicle-Stimulating Hormone-Induced Aromatase Activity by Androgens in Cultured Rat Granulosa Cells*

Abstract

Experiments were performed to determine whether androgens, in enhancing estrogen secretion in rat granulosacells, act solely as substrates for FSH-induced aromataseactivity or whether they also participate in the mechanism bywhich FSH increases the activity of the enzyme. Granulosa cellswere isolated from 27-day-old rats and cultured during a 24- or36-h induction period in the presence of FSH (0.5 μg/ml MRSFSHor 1.0 μg/ml NIH-FSH-Sll) with or without testosterone(0.5 μM) or other steroids. The cells were then cultured for afurther 6- to 12-h test period in medium containing no addedhormones or testosterone, an aromatizable androgen. The production of 17β-estradiol during the test period was measured as an index of aromatase activity stimulated by treatments during the induction period. In the absence of FSH during the induction period, estrogen biosynthesis was very low during both induction and test periods. The addition of FSH alone during the induction period resulted in significantly increased estrogen synthesis during the test period in the presence of testosterone. Without the availability of aromatizable substrate during the test period, estrogen synthesis was undetectable. The addition of aromatizable substrate and FSH during the induction period brought about a significant increase in the rate of estrogen accumulation during the test period in which testosterone was present. The presence of dihydrotestosterone (0.5 μM) or androsterone (0.5 μM), both nonaromatizable androgens, during the induction period also significantlyenhanced the FSH effect during the test period when testosterone was present, although this was only 50–60% as effective as treatment during the induction period with testosterone. The presence of progesterone (0.5 μM) with FSH duringthe induction period failed to increase aromatase activity above that induced by FSH alone.It is concluded that androgens are able to specifically regulate estrogen biosynthesis by granulosa cells collected from imm turerats both by acting as substrates for the FSH-induced aromatase enzyme activity and by participating in the mechanism by which FSH increases the activity of the enzyme.