INDUCED LUTEAL REGRESSION - DIFFERENTIAL-EFFECTS ON FOLLICULAR AND LUTEAL INHIBIN ACTIVIN SUBUNIT MESSENGER-RNAS IN THE MARMOSET MONKEY

During the luteal phase of the primate ovulatory cycle the predominant inhibin/activin subunit mRNAs produced by the corpus luteum and antra l follicles are those for the alpha- and beta(B)-subunits respectively . The control of expression of these mRNAs and the resultant nature of the endocrine and paracrine signals which they may potentially genera te has yet to be elucidated. Inhibin/activin subunit mRNAs may have a role in both the paracrine regulation of follicular and luteal functio n and modulation of FSH secretion. The aim of this study was to invest igate the expression of inhibin/activin subunit mRNAs following luteal regression induced by either withdrawal of LH support (GnRH antagonis t treatment), or by a direct inhibitory action (prostaglandin administ ration). Marmoset monkeys with regular ovulatory cycles were treated o n day 8 and 9 of the luteal phase with either GnRH antagonist, prostag landin or vehicle (n=3 per group). Ovaries were studied 48 h after ons et of treatment (on day 10 of the luteal phase) by hybridizing frozen tissue sections with radiolabelled riboprobes specific to the inhibin/ activin alpha-, beta(A)- and beta(B)-subunit mRNAs. After autoradiogra phic exposure, grain concentrations were quantified by image analysis. In corpora lutea h-om control marmosets there was high expression of alpha-mRNA with only marginal expression of beta(B)-mRNA. Corpora lute a in animals treated with GnRH antagonist or prostaglandin had markedl y reduced expression of alpha-mRNA while beta(B)-mRNA was unchanged. I n controls, all healthy antral follicles exhibited a high level of exp ression of beta(B)-mRNA in the granulosa cells and low expression of a lpha-mRNA in theca cells. This was unaffected by either treatment. bet a(A)-mRNA was found at a low level in granulosa cells but was not evid ent at a significant level in the corpora lutea of any of the groups. These results demonstrate (1) the marmoset corpus luteum is a source o f high expression of alpha-subunit mRNA, (2) this alpha-mRNA is depend ent upon LH support, (3) the process of luteal regression takes place without alteration of beta(B)-mRNA. Antral follicle alpha- and beta(B) -mRNAs are independent of the process of luteal regression or gonadotr ophic withdrawal during the period of the luteal-follicular phase tran sition.