Effects of hyperthermia on uterine blood flow and shunting through uterinearteriovenous anastomoses in the late-pregnant ewe

The effect of maternal hyperthermia on uterine blood flow (UBF) through thr two main uterine arteries and on the proportion of UBF shunted through ute rine arteriovenous anastomoses (AVAs) was investigated. Eight late-pregnant ewes were exposed to normothermic (22-23 degrees C) or hyperthermic (appro ximately 39 degrees C) ambient conditions for 8 h. UBF was measured in the left and right uterine arteries using flow probes and microspheres were inj ected into the uterine artery before, during and after the experimental per iod. The distribution of microspheres between the uterus and lungs was dete rmined to calculate changes in capillary and AVA blood flows. Hyperthermia produced a significant (P<0.05) increase in maternal core temperature (+1.5 degrees C), increase in maternal blood pH (+0.21; P<0.05) and decrease in maternal pCO(2) (-16.2 mmHg; P<0.05). Blood flow to the uterine horn ipsila teral to the corpus luteum (CL) remained unchanged during hyperthermia, whe reas total UBF and blood flow to the contralateral uterine horn were signif icantly decreased (P<0.05), by 23.1% and 20.8%, respectively, of pre-heat c ontrol values. The proportion of UBF shunted through uterine AVAs during hy perthermia was not significantly different from values observed in normothe rmic ewes (21.9 +/- 0.7%). Mild to moderate hyperthermia in late-pregnant s heep induces respiratory alkalosis and decreases total blood flow to the ut erus, brought about by a decrease in blood flow to the uterine horn contral ateral, but not ipsilateral to the CL. Heat treatment does not alter the pr oportion of UBF traversing uterine AVAs.