Prostaglandin secretion by endometrium of pregnant and cyclic cattle at Day 17 after oestrus in response to in-vitro heat stress

Abstract

Bilateral perifusion devices were utilized to measure prostaglandin F-2α (PGF) secretion by bovine endometrium in response to in-vitro heat stress. Tissues were collected at Day 17 after oestrus from cyclic (N = 4) and pregnant (N = 5) cows, placed into 3 perifusion devices, perifused (3 ml/10 min, Krebs-Ringer-bicarbonate [KRB]) for 5 h, and fractions were collected every 10 min. Endometrial tissues within each device were subjected to a different temperature and oxytocin (1 i.u./ml KRB) treatment sequence: (1) control-oxytocin: 1 h at 39°C; 2 h at 39°C, 0.5 h at 39°C with oxytocin, 0.5 h at 39°C and 1 h at 39°C; (2) heat-oxytocin: 1 h at 39°C, 2 h at 42°C, 0.5 h at 42°C with oxytocin, 0.5 h at 42°C and 1 h at 39°C; (3) heat-KRB; 1 h at 39°C, 2 h at 42°C, 0.5 h at 42°C, 0.5 h at 42°C and 1 h at 39°C. Regardless of reproductive status, heat stress induced a rapid increase (P < 0.01) in PGF secretion rates. Oxytocin induced an increase (P < 0.01) in PGF secretion for endometrium from cyclic cows regardless of temperature. Endometrium from pregnant cows did not respond to oxytocin when perifused at 39°C. However, PGF secretion rates from endometrium of pregnant cows increased (P < 0.01) in response to oxytocin when perifused under heat stress conditions. Increased PGF secretion rates and responsiveness to oxytocin for endometria from pregnant cows in response to heat stress suggests that the ability of the conceptus to inhibit uterine PGF-2α synthesis may be compromised during early pregnancy when cattle are subjected to high ambient temperatures.