AJP - Endocrinology and Metabolism, Vol 256, Issue 6 E852-E862, Copyright © 1989 by American Physiological Society
Effect of continuous feeding on maternal protein metabolism and fetal growth in the rat
P. R. Ling, B. R. Bistrian, G. L. Blackburn and N. Istfan
Cancer Research Institute, New England Deaconess Hospital, Harvard Medical School, Boston, Massachusetts 02215.
Accelerated maternal catabolism ensures adequate fetal growth in the
postabsorptive pregnant mammal during late gestation. However, the relative
importance of maternal stores and diet in supplying nutrient requirements
to the fetus is unknown. We have measured rates of protein synthesis and
breakdown in maternal and fetal tissues during continuous intravenous
feeding on days 17 and 20 in the rat, using leucine tracer infusions.
Nutrient solutions supplying 180 and 250 kcal.kg-1.day-1 were tested.
Changes in fetal size were measured in these rats and in rats maintained on
ad libitum chow feeding. In comparison to previous results in the
postabsorptive rat, leucine flux from endogenous sources into plasma was
significantly suppressed, with only 12-20% of circulating leucine derived
from maternal tissues. Muscle protein catabolism (previously described on
day 20 of gestation) was abolished with continuous feeding. Fetal growth
rate averaged 46%/day on day 17 of gestation in all groups but was reduced
to 12%/day on day 20 in the rats intravenously fed 180 kcal.kg-1.day-1 and
22%/day in the rats fed 250 kcal.kg-1.day-1. Fetal growth on day 20 in the
rats fed rat chow ad libitum was unaffected. We conclude that by decreasing
the maternal contribution to circulating nutrients, continuous intravenous
feeding may adversely affect fetal growth in late pregnancy. The findings
in the current study underline the physiological importance of
maternal-fetal nutrient exchange.
