The relation of maternal blood volume to plasma renin activity in the pregnant rabbit.

Blood volume, estradiol 17 beta and estrone concentrations, and plasma renin activity were determined weekly in 26 chronically catheterized nonanesthetized rabbits during pregnancy and after delivery. We determined blood volume by 99technetium, and plasma volume by the microhaematocrit method. The values for whole blood volume were 52.7 (+/- 2.3) and 63 (+/- 2.2) ml X kg-1 for nonpregnant and pregnant animals, respectively. During the course of gestation plasma renin activity increased about 300%, but estradiol 17 beta and estrone concentrations did not change significantly. The increase in whole blood and plasma volumes during pregnancy correlated highly with the increase in plasma renin activity, r = 0.53 and 0.59, respectively.