ABSTRACT. The effects on the conceptus of persistently decreased maternal plasma amino acid concentrations were studied in pregnant rats by the infusion of glucagon (0.21 mglday) to the mother from day 14 to 20 of gestation with a subcutaneous, osmotically driven minipump. Controls received diluent. The experimental animals either had normal caloric intake and weight gain, or diminished caloric intake with no weight gain. Both experimental groups exhibited a decrease in plasma total amino acid concentration of approximately 50%. Maternal plasma glucose and insulin concentrations were unaffected except for slight decreases in the low weight gain group. At cesarean section on day 20, fetal weight was unaffected in the normal weight gain group, while the low weight gain animals exhibited intrauterine growth retardation. Fetal plasma glucose and insulin concentrations were unaffected. Despite the marked decrease in maternal plasma total amino acid concentration, fetal plasma total amino acid concentration was unaffected. Individual plasma amino acid concentrations in the normal weight gain mothers and fetuses revealed a spectrum of changes. Some maternal amino acids were decreased by more than 60% (a-aminobutyric acid, asparagine, threonine, glutamine, alanine) while others were unaffected (tyrosine, tryptophan, phenylalanine, histidine). In general, amino acids that were decreased in the mother exhibited no change or a lesser decrease in fetal plasma concentration, while those that were unaffected in the mothers showed increased fetal concentrations. Fetuses from the low weight gain mothers had plasma amino acid ~rofiles that were similar to those of the normal weight gain mothers. We speculate that the preserved fetal amino acid concentrations are due to enhanced placental transport of amino acid secondary to maternal substrate decrease. (Pediatr Res 20: 1071-1076,1986 which are specific for each group of nutrients. In the case of amino acids it has been demonstrated that the placenta is capable of concentrating most amino acids intracellularly in order to achieve transport to the fetus against a concentration gradient (1-4). This results in fetal plasma amino acid concentrations which can be more than three times higher than maternal plasma concentrations (1, 5 , 6).Maternal substrate limitation, presumably by limiting nutrient transport to the fetus, can lead to IUGR. This has been demonstrated experimentally in models utilizing starvation (7) or ligation of the uterine artery (8). These manipulations result in nonspecific reduction in the delivery of substrates, including glucose and amino acids, such that the roles of specific substrates remain obscure.The aim of the present study was to develop a model in which maternal plasma amino acid concentrations are selectively reduced without significant changes in the maternal concentrations of other nutrients. In nonpregnant male rats, a persistent increase in glucagon has been shown to be associated with a decrease in total plasma amino acid concentrations (9). Thi...

Louis, MO 1's role via its R in the brain, unlike other organs is unknown. Hypothyroidism(HP) influences fetal(f) lung and liver IR and retards B metabolism. The ontogeny of B IR in plasma membranes(PM) was examined to explore the role of I in rabbit F (30d.) and newborn(N) B (ld,6d). Groups with PTU-induced HP(Fand N), N with Tq corrected HP (ET) and hyperthyroidism(HT) were also studied. Specific lZ51-1 binding/ZOOug BPM (IB), IR no.xlOlOmg prot .-' and affinity (~ix10~=0.91k.08) were determined.