THE EFFECT OF OXYTOCIN ON PROGESTERONE SECRETION, PHOSPHOINOSITIDE HYDROLYSIS AND INTRACELLULAR MOBILISATION OF CA2+ IN PORCINE LUTEAL CELLS

Oxytocin (OT) is involved in the regulation of steroid secretion by the corpus luteum (CL) in pigs, but OT signal transduction in the porcine CL has not been identified. In this study, the effects of OT on in vitro progesterone (P-4) secretion, phosphoinositide (PI) hydrolysis and intracellular mobilisation of Ca2+ ([Ca2+](i)) were investigated in porcine luteal cells during the early (days 3-5), mid( days 8-10) and late luteal phases (days 12-14) of the oestrous cycle. Basal concentrations of P-4 and accumulation of inositol phosphates (IPs) were higher (P < 0.05) on days 3-5 and 8-10 of the oestrous cycle than on days 12-14. Basal [Ca2+](i) mobilisation did not differ among studied periods of the oestrous cycle. Oxytocin (10(-7) M) enhanced P-4 secretion and PI hydrolysis (P < 0.05) by luteal cells harvested on days 8-10 of the oestrous cycle. Moreover, OT started to increase mobilisation of [Ca2+](i) at the 15th (days 3-5 and 8-10) or 30th second (days 12-14) in porcine luteal cells. It was concluded that in pigs OT acts as a regulator of steroidogenesis, stimulating P-4 secretion in mature CL. This OT action may be mediated by changes in PI hydrolysis and [Ca2+](i) mobilisation.