Effects of Streptozotocin-Induced Diabetes in Pregnant Rats on Placental Transport and Tissue Uptake of α-Amino-Isobutyric Acid

 

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Summary

Placental transport and tissue uptake of amino acids were studied in streptozotocin(STZ)-induced diabetic rats by using the non-metabolizable amino acid [U-14C]-α-amino-isobutyric acid (AIB). Fifteen minutes prior to autopsy, animals of each group, control (C), diabetic (D), diabetic-insulin treated (Dl) and diabetic-T₄ followed by 3-5-Dimethyl-3′-isopropyl-L-thyronine (DIMIT) treated (DTD), received an injection of the [U-14C]-AIB SC. Disintegrations per minute (DPM) were measured in serum and tissues subsequent to autopsy. There were no differences in maternal serum DPM/ml among groups. Fetal serum DPM, however, were lower in D and DTD groups than in the C group. The whole fetal tissue homogenate radioactivity was lower in the D, DTD, and DI groups than in the C group. In general, more AIB was taken up by fetal tissues of C than D animals. Maternal liver AIB uptake was reduced in D, DI, and DTD from C animals and net placental transport of AIB was less in D and DTD than C animals. Fetal liver protein concentrations were depressed in D and DTD animals from C and Dl, but fetal brain protein concentrations showed no significant differences. Furthermore, the lower organ and fetal body weights of the D and DTD groups compared with the C and Dl groups support the proposal that fetal anabolism is impaired. Maternal and fetal serum T₄ concentrations were lower in D and DTD than in C and DI animals. Insulin therapy improved serum T₄ levels in both mother and fetuses. It did not, however, correct all other measured parameters. The thyroxine-DIMIT treatment significantly corrected few parameters.

The data support the theory that alterations in fetal amino acid levels may result from changes in placental transfer of amino acids from the maternal to the fetal compartment. They further suggest that uptake of amino acids by specific maternal and fetal tissues is compromised.