MODEST RESTRICTION OF DIETARY-PROTEIN DURING PREGNANCY IN THE RAT - FETAL AND PLACENTAL GROWTH

Pregnant rats were fed to appetite on diets containing 6, 9, 12 or 18% protein and the fetuses were delivered at 20 days. Compared with the 18% protein diet (7.4 MJ), there was a significant increase in food an d energy intake in the rats on the 9% (8.7 MJ) and 12% (8.4 MJ) diets, but not on the 6% (7.4 MJ) diet. The efficiency with which the dietar y energy was used for weight gain was reduced on the 6, 9 and 12% diet s compared with the 18% diet. The trend towards a decrease in the numb er of viable fetuses and an increase in the number of resorptions on t he 9% and 6% diets did not reach statistical significance. The placent al weight was not different to the 18% group (520 mg) on the 12% diet (540 mg), but was significantly increased on the 9% diet (590 mg) and significantly decreased on the 6% diet (510 mg). Fetal weight was grea test on the 12% diet (1.81 g) and significantly decreased on the 9% di et (1.71 g). The fetal:placental ratio, around 3.3 for the 18 and 6% d iets, was significantly increased on the 12% diet (3.7) and significan tly decreased to 2.9 on the 9% diet. After adjusting for the effect of the fetal position in the uterine horn, the number of pups per litter and an estimate of the number of failed implantations the effect of d iet on placental weight was no longer statistically significant, but t he effect of dietary protein on fetal weight was more significant stat istically, with little change overall on the fetal:placental ratio. Th e weight of the fetal pancreas was significantly increased on the 12% diet and increased relative to body weight on the 12% and 9% diets, bu t significantly decreased on the 6% diet. Maternal liver weight, place ntal weight and fetal liver weight/body weight were all significantly increased on the 9% diet. It is concluded that the maternal and fetal response to diets low in protein during pregnancy is a complex interac tion of the overall energy intake, and the ability of the protein cont ent of the diet to satisfy the competitive metabolic demands for place ntal and fetal growth relative to the effective demand for amino acids for the handling of the dietary energy.