EFFECTS OF HEAT-STRESS AND OXYTOCIN ON PLASMA-CONCENTRATIONS OF PROGESTERONE AND 13,14-DIHYDRO-15-KETOPROSTAGLANDIN F2-ALPHA IN GOATS

The objectives of this study were to determine the effects of heat stress (HS; 37 degrees C 12 h day(-1), 30 degrees C 12 h day(-1)) on plasma concentrations of progesterone (P), 13,14-dihydro-15-ketoprostaglandin F-2a (PGFM), and oxytocin (OXY) induced secretion of PGFM in pregnant goats, Goats experienced constant relative humidity (35%) with either HS (n=16) or thermoneutral (TN; 21 degrees C; n = 20) temperatures from Day 8 to Day 17 of pregnancy. Respiration rates were elevated (P < 0.01) during the experiment in HS compared to TN goats. Morning (HS, 39.4 +/- 0.06 degrees C; TN, 38.9 +/- 0.06 degrees C) and afternoon (HS, 39.7 +/- 0.11 degrees C; TN, 38.9 +/- 0.11 degrees C) rectal temperatures were also elevated (P < 0.01) by HS. Plasma levels of PGFM tended to be higher (P = 0.08) in pregnant goats exposed to HS compared to those maintained at TN temperatures (458.1 +/- 37.4 and 360.4 +/- 37.0 pg ml(-1), respectively). Oxytocin did not affect plasma PGFM concentrations in pregnant goats (P > 0.1) but elevated plasma PGFM concentrations in bred/non-pregnant goats (oxytocin X time, P < 0.01). Pregnant goats exposed to HS had elevated plasma concentrations of P in the afternoon (HS, 8.33 +/- 0.36 ng ml(-1); TN, 6.38 +/- 0.42 ng ml(-1)) but not in the morning (HS, 6.84 +/- 0.42; TN, 6.58 +/- 0.42 ng ml(-1); temperature X time, P < 0.05). Therefore, elevated ambient temperatures during Days 8-17 of pregnancy increased plasma concentrations of P and PGFM in pregnant goats. A rise in uterine prostaglandin secretion may influence corpus luteum function during early pregnancy and affect conceptus growth and development.