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 antral 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 generate has yet to be elucidated. Inhibin/activin subunit mRNAs may have a role in both the paracrine regulation of follicular and luteal function and modulation of FSH secretion. The aim of this study was to investigate the expression of inhibin/activin subunit mRNAs following luteal regression induced by either withdrawal of LH support (GnRH antagonist treatment), or by a direct inhibitory action (prostaglandin administration). Marmoset monkeys with regular ovulatory cycles were treated on day 8 and 9 of the luteal phase with either GnRH antagonist, prostaglandin or vehicle (n=3 per group). Ovaries were studied 48 h after onset 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 autoradiographic 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 lutea in animals treated with GnRH antagonist or prostaglandin had markedly reduced expression of alpha-mRNA while beta(B)-mRNA was unchanged. In controls, all healthy antral follicles exhibited a high level of expression of beta(B)-mRNA in the granulosa cells and low expression of alpha-mRNA in theca cells. This was unaffected by either treatment. beta(A)-mRNA was found at a low level in granulosa cells but was not evident at a significant level in the corpora lutea of any of the groups. These results demonstrate (1) the marmoset corpus luteum is a source of high expression of alpha-subunit mRNA, (2) this alpha-mRNA is dependent 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 gonadotrophic withdrawal during the period of the luteal-follicular phase transition.