Release of immunoreactive oxytocin and neurophysin I by cultured luteinizing bovine granulosa cells

We investigated the production of oxytocin (OT) and oxytocin-neurophysin (bNpI) by bovine granulosa cells cultured in presence of 10% foetal calf serum, a condition known to induce spontaneous luteinization of these cells. The production of immunoreactive (ir) OT was significantly higher in the cultures harvested from large follicles than in those derived from small follicles. Chromatography on Sephadex G-25 showed similar elution sites of ovarian and synthetic OT, while HPLC revealed two peaks of irOT, one of which (±65%) coincided with synthetic OT. In another experiment, we could observe a gradual increase of OT, bNpI, and progesterone production by granulosa cells derived from large follicles, in relation with the incubation time. These data show that bovine granulosa cells are able to produce OT and bNpI, probably by an active biosynthesis as observed in the hypothalamo-neurohypophysial system and that the granulosa productions of OT, bNpI and progesterone are closely related.