Expression of inhibin/activin alpha, beta A and beta B subunits in the ovary of the bitch

Inhibins and activins are glycopeptides mainly produced by gonads. The present investigation is aimed at immunolocalizing inhibin/activin alpha, betaA and betaB subunits in normal ovaries of cyclic bitches. The granulosa cells of growing follicles and luteal cells are the main sites of ovarian inhibin/activin production in the bitch. The expression of the inhibin/activin alpha, betaA and betaB subunits in preantral follicles suggests an important role of these peptides as local gonadotrophin independent growth factors. The negative immunostaining for the inhibin alpha subunit in preovulatory follicles and its subsequent variability in the dioestrous corpus luteum, seem to be related to the circulating levels of inhibin, FSH, 17beta-oestradiol and progesterone, in the bitch. The expression of beta subunits in the granulosa cells and oocytes of preovulatory follicles may indicate a local role in the maturation of the oocyte. In conclusion, it can be stated that inhibins and activins are very important peptides involved in the regulation of the oestrous cycle of the bitch.