Measurement of organ blood flow using tritiated water. II. Uterine blood flow in conscious pregnant ewes.

Total uterine blood flow was measured with a tritiated water (TOH) diffusion method and with radioactive microspheres in six, conscious, pregnant ewes. With continuous infusion of TOH, equilibrium between the TOH concentration in utero-ovarian venous blood and arterial blood was attained within 50 min of the start of the infusion. The concentration of TOH in uterine and foetal tissue and in foetal blood water was the same as that in uterine venous water by 40 min; at this time, the concentration of TOH in the water of amniotic and allantoic fluids was 96% of that in uterine venous blood water. Estimates of total uterine blood flow obtained using TOH were highly correlated with those obtained with microspheres (r = 0.889, P less than 0.001, n = 8) and the corresponding mean (+/- s.e.m.) flow values obtained with the two techniques (1030.5 +/- 110.6 and 1006.2 +/- 100.0 ml min-1, respectively) did not significantly differ. The percentage of the total uterine blood flow passing through arteriovenous anastomoses ranged from 1.4 to 3.3%.