Abstract
Oxytocin and vasopressin are related peptides that have receptors in the uterus. Species from families other than Suidae produce only arginine-vasopressin; in contrast, pigs apparently express both arginine- and lysine-vasopressin. The aim of this study was to determine whether arginine- or lysine-vasopressin would activate phospholipase C, increase intracellular calcium concentration [Ca2+](i) and stimulate PGF(2 alpha) production in enriched cultures of stromal, glandular epithelial and luminal epithelial cells from pig endometrium. Cells were obtained from gilts on day 16 after oestrus by differential enzymatic digestion and sieve separation. After 96 h in culture, the cells were treated with 0 or 100 nmol arginine- or lysine-vasopressin I-1. The responses to 100 nmol oxytocin I-1 and 100 nmol GnRH I-1 were used as positive and negative controls, respectively. Consistent with previous results, oxytocin stimulated phospholipase C activity (P < 0.05), increased [Ca2+](i) (P < 0.05) and promoted PGF(2 alpha) secretion (P < 0.05) from stromal and glandular epithelial cells. Activity of phospholipase C, [Ca2+](i) and PGF(2 alpha) release were also increased (P < 0.05) by arginine-vasopressin in stromal cells, but the responses were less (P < 0.01) than those induced by oxytocin. An oxytocin antagonist attenuated the [Ca2+](i) response of stromal cells to both oxytocin and arginine-vasopressin. Sequential treatment of cells with oxytocin and arginine-vasopressin indicated that oxytocin desensitized the response to oxytocin, but arginine-vasopressin did not similarly desensitize the response to oxytocin. In glandular and luminal epithelial cells, arginine-vasopressin did not stimulate phospholipase C activity, [Ca2+](i) or PGF(2 alpha) secretion. Neither GnRH nor lysine-vasopressin induced phospholipase C activity, increased [Ca2+](i) or stimulated PGF(2 alpha) production in any endometrial cell type. These results indicate that oxytocin receptors can bind arginine-vasopressin more readily than they bind lysine-vasopressin. Type 1 vasopressin receptors may also exist in endometrium predominantly on cells other than stromal, glandular epithelial and luminal epithelial cells, as in previous studies both arginine-vasopressin and lysine-vasopressin stimulated phospholipase C activity in endometrial explants to a similar extent as oxytocin.