Regulatory role of inhibin in follicle-stimulating hormone secretion and folliculogenesis in the guinea pig

The effects of unilateral and bilateral ovariectomy and passive immunizatio n against inhibin on follicle-stimulating hormone (FSH) secretions and foll icular development in the guinea pig were investigated. Bilateral ovariecto my decreased plasma immunoreactive (ir-) inhibin rapidly and increased plas ma FSH significantly. Unilateral ovariectomy decreased plasma ir-inhibin an d increased plasma FSH temporarily, and doubled the number of ova released from the remaining ovary at the subsequent ovulation in guinea pigs. Inject ion of 1.0 ml inhibin antiserum significantly increased concentrations of p lasma FSH at 6 hr onwards and the number of small follicles (100-200 mum in diameter) at 48 hr after the injection in guinea pigs bearing progesterone -containing implants. In vitro bioassay showed that inhibin antiserum could neutralize the suppression of ovarian homogenate on FSH secretion from cul tured rat anterior pituitary cells. These results confirm the evidence that the ovary is the main source of inhibin secretion and both in vitro bioass ay and passive immunization against inhibin show that the inhibin is a majo r regulator in the follicular development through FSH secretion in guinea p igs.