Cardiac output and uteroplacental blood flow were measured by using 15-microns 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.
The effects of the following dietary regimes on maternal body weight and weights of the products of conception were investigated in the laboratory rat: 50% dietary restriction during the catabolic phase (days 15--21) of gestation; 50% dietary restriction during the anabolic phase (days 1--14) but adequate nutrition during the catabolic phase, and 50% dietary restriction throughout gestation. Total body weight and net maternal weight at term were significantly reduced in all three test groups. Restricting dietary intake during the anabolic phase resulted in decreased maternal weight gain. Feeding an adequate diet during the catabolic phase, following restriction during the anabolic phase, caused only a slight decrease in net maternal weight, while term fetal weight approximated that of controls. Dietary restriction during the catabolic phase, or throughout gestation, caused increased net maternal weight loss. Term fetal weight in both groups was significantly lower than that of the controls, but not different from each other. The results indicate that the dam is able to mobilize nutrients stored during the anabolic phase of pregnancy. Mobilization of these nutrients did not significantly increase fetal growth, however, supporting the hypothesis that the dam is able to compartmentalize available nutrients during malnutrition and prevent serious depletion of these stores by the fetus.
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