RELATION OF MATERNAL BLOOD-FLOW WITHIN THE UTERUS TO CHANGE IN SHAPE AND SIZE OF THE CONCEPTUS DURING PREGNANCY; PHYSIOLOGICAL BASIS OF UTERINE ACCOMMODATION
Circulation rates [image] of NaCN were detd. from different parts of the venous system, and the maternal carotid body. The sites employed were the lateral uterine vein within the wall of the uterus at conceptussites; the same vein at interconceptus sites; the same vein in sterite contralateral uterine horns; and the femoral veins. A total of 54 rabbits were employed on the 1st, 12th, 16th, 20th, 22d, .24th, and 28th days of pregnancy. A total of 854 respiratory responses (circulation times) were made. Results showed (1) a decrease in systemic circulation rate during the first half of pregnancy (16 days), followed by a transient return to normal on the 22d day, and a subsequent decrease; (2) about the conceptus there is a progressive decrease in circulation rate till the 20th day (to 66% of pre-pregnancy level). Upon attainment of maximum spherical size (22d day) a profound decrease in circulation rate occurs (to 25% of pre-pregnancy level); at this point the conceptus elongates and there is a restoration of blood-flow with this change in shape to 75% of the pre-pregnancy level. Blood-flow at interconceptus sites, when these are on the spherical stage, is equal to that found at the beginning of pregnancy. Relations of these changes to local hydrostatic conditions are noted, and the relation to fetal growth, uterine growth and rearrangement of the blood vessels within the uterus are discussed.