Relaxin and prostaglandin on oxytocin secretion from bovine luteal cells during different stages of gestation

Abstract

The objective of this study was to determine whether bovine luteal cells from different stages of gestation secrete oxytocin and whether relaxin, cloprostenol (a potent analogue of prostaglandin F2 alpha), estradiol-17 beta, and LH can acutely alter oxytocin secretion. Bovine luteal cells (10(5)) were cultured for 24 h without treatment and with medium-hormone replacement every 24 h. Oxytocin was quantified by radioimmunoassay of the culture media. Basal oxytocin secretion was similar (22-31 pmol/l, p less than 0.05) for all stages of gestation (days 100, 145, 160, 185, 200, 210, and 240). Relaxin induced a dose-dependent suppression of oxytocin release. After 24 h of incubation, addition of 0, 16.7, 83.5, and 167 nmol/l porcine relaxin (3000 U/mg) induced 54 +/- 4, 105 +/- 16, 47 +/- 4, and 38 +/- 4 pmol/l of oxytocin in cells from 160-day-old corpora lutea and 138 +/- 12, 21 +/- 2, 19 +/- 3, and 15 +/- 2 pmol/l oxytocin in cells from 240-day-old corpora lutea. From luteal cells of 160- and 240-day-old corpora lutea, 2 micromol/l cloprostenol induced a marked increase (p less than 0.01) of 208 +/- 39 and 371 +/- 34 pmol/l oxytocin, respectively. Addition of 167 nmol/l relaxin did not prevent cloprostenol-induced oxytocin secretion during the first 48 h, but a decrease (p less than 0.05) in oxytocin occurred in day 3 cell cultures. These results indicate that cultured luteal cells obtained from different stages of gestation in cattle can secrete oxytocin and suggest a role for relaxin in the regulation of oxytocin release.