Effect of Dietary Restriction, during the Last Week Only or throughout Gestation, on Cardiac Output and Uteroplacental Blood Flow in Pregnant Rats

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Abstract
Cardiac output and uteroplacental blood flow were measured by using 15-µm radioactive labeled microspheres in ad libitum-fed nonpregnant female rats, and in pregnant rats: 1) fed ad libitum; 2) fed a 50% restricted diet from day 14 of gestation on; and 3) fed a 50% restricted diet from day 5 of gestation on. Dietary restriction induced fetal growth retardation regardless of duration. Cardiac output in both groups of diet-restricted dams was 30% less than that of the ad libitum-fed pregnant dams, and not significantly increased above that of the nonpregnant rats. Total uterine and placental blood flows in the dams fed the restricted diet during the last week of gestation were reduced 30–35% relative to the ad libitum-fed dams due to the reduced cardiac output. In the dams fed the restricted diet from day 5, total uterine and placental blood flows were reduced 60–65% due to both the reduced cardiac output and a decreased fractional distribution of cardiac output to the uterus. Dietary treatment had no effect on blood flow to the kidneys and ovaries. The results suggest that the reduced placental blood flow associated with maternal malnutrition-induced fetal growth retardation is caused by an inadequate expansion of maternal cardiac output, and, if malnutrition is severe enough, a fractional redistribution of cardiac output away from the uterus and developing conceptus occurs.