Effects of pregnancy and systemic or intrauterine oxytocin infusion on the distribution of endometrial oxytocin receptors in the ewe: an autoradiographic study.

Previous autoradiographic studies have suggested that the regulation of oxytocin receptors differs between endometrial cell types during the ovine oestrous cycle, and that those present on luminal epithelial cells are of particular importance to the regulation of prostaglandin F2 alpha release during luteal regression. The present autoradiographic study compares the distribution of the endometrial oxytocin receptor in day-15 non-pregnant and pregnant ewes. The distribution of the endometrial oxytocin receptor in day-15 non-pregnant ewes infused with systemic or intrauterine oxytocin has also been investigated. Continuous, s.c. infusion of oxytocin (150 mmol/24 h) into ewes (n = 6) between days 10 and 15 of the oestrous cycle significantly increased plasma oxytocin concentrations (to approximately 100 pmol/l). There was no similar increase in systemic oxytocin concentrations in ewes receiving intrauterine (i.u.) oxytocin infusions (10 nmol/24 h) between days 10 and 15 of the oestrous cycle (n = 6). Luteolysis was inhibited in all six animals infused with oxytocin (s.c.) and endometrial oxytocin receptor concentrations were significantly lower on day 15 in these animals (12.8 +/- 6.5 (S.E.M.) fmol/mg protein; P < 0.001) and in pregnant ewes (18.4 +/- 15.4 fmol/mg protein; P < 0.001; n = 8) than in ewes infused with saline (248.6 +/- 67.1 fmol/mg protein; n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)