Endogenous hormones and regulation of uterine blood flow during pregnancy

Fourteen pregnant sheep were prepared for measurements of blood flow through a major uterine artery (UBF) and of arterial concentrations of estrone, estradiol, and progestagen. Five of the animals were ovariectomized. Measurements were made daily (n = 12) or every 4 h for 24 h (n = 4). Statistically significant (P less than 0.01) correlation coefficients were detected between UBF and hormone, either alone or in combination; the closest and most consistent associations were those in which estrogen and progestagen concentrations were summed or multiplied. Ewes with higher hormonal concentrations were those that had the higher rates of UBF. Correlation coefficients were statistically significant more often among ovariectomized animals. No associations were detected within one animal that delivered a growth-retarded fetus nor from any of the 24-h data. Estrogens and progestagen accounted for as much as 25% of the daily variation of UBF among and within sheep during the last half of pregnancy.