Protein turnover in rat placenta: effects of maternal fasting and maternal protein restriction

Biochemical composition and variables of protein turnover were determined in rat placenta at 21 days gestation in control animals and in animals subjected to 72-h fasting and protein/calorie restriction (6 per cent protein) throughout gestation. Placental protein synthesis was determined following the injection of 'massive' amounts of 14C-phenylalanine intravenously to the pregnant rat. Protein content was reduced in placentas from rats that were fasted for 72 h and in those who were protein restricted throughout pregnancy. Placental RNA content was significantly reduced only in the protein-restricted animals. Fractional rates of protein synthesis were reduced in placentas from the protein-restricted animals (Ks = 17.9 +/- 0.8 per cent per day in controls versus 11.7 +/- 0.9 in protein restricted, P = 0.002), but not in fasted animals. Fractional protein breakdown was markedly enhanced in placentas following maternal fasting (Kd = 9.9 per cent per day in controls versus 26.0 per cent in fasted), but not affected by protein deprivation. These results mimic those previously reported for other fetal tissues under these experimental conditions.