The effect of progesterone on oxytocin-stimulated intracellular Ca2plus mobilisation and prostaglandin secretion in porcine endometrium

We have studied in the porcine endometrium the expression of oxytocin receptor (OTR) mRNA and the effect of progesterone (P₄) on oxytocin/oxytocin receptor (OT/OTR) function concerning intracellular Ca²⁺mobilisation ([Ca²⁺]i), prostaglandin F2α (PGF2α) and E2 (PGE2; PG) secretion. Tissue was taken from cyclic and early pregnant pigs (days 14-16). A higher expression of OTR mRNA (P<0.05) was observed in the endometrium of cyclic than pregnant pigs. The stimulatory (P<0.05) effect of OT (10⁻⁷ M) on [Ca²⁺]i mobilisation was noticed within 15-60 s and 30-60 s in endometrial stromal cells of cyclic and pregnant pigs, respectively. In the presence of P₄ (10⁻⁵ M) basal and OT-stimulated [Ca²⁺]i concentrations decreased in stromal cells during luteolysis and pregnancy. In stromal cells P₄ delayed mobilisation of [Ca²⁺]i in response to OT by 15 s during luteolysis and had no effect during pregnancy. In cyclic and pregnant epithelial cells OT stimulated mobilisation of [Ca²⁺]i in 45 s and 60 s, respectively. Oxytocin increased (P<0.05) PGF2α secretion during luteolysis and pregnancy and PGE2 during luteolysis from endometrial slices. Progesterone did not inhibit this stimulatory effect. During luteolysis OT increased (P<0.05) PGF2α in epithelial and stromal cells and PGE2 secretion in epithelial cells. In the presence of P₄ this effect of OT was reduced only in stromal cyclic cells (6 h culture). The presence of P₄ decreased the effect of OT on [Ca²⁺]i mobilisation only in stromal cells. We found that, in most conditions, P₄ did not inhibit the OT-stimulated secretion of PG in the porcine endometrium.