THE EFFECT OF THYROXINE(T4) AND DEXAMETHASONE(Dx) ON FETAL(F) HEART(H) AND BRAIN(B) INSULIN RECEPTOR (IR)

Abstract

Insulin mediated tissue glucose uptake and lipid synthesis as well as F lung and liver IR are modulated by T4 and Dx. Using plasma membranes(PM) 125I-insulin binding(IB) per 100μg HPM/200 μg BPM and IR ×1010mg protein−1 in two highly glucose dependent fetal organs (H and B), were studied under conditions of T4 and steroid excess. Date bred rabbits(M) received T4 at 50μg/kg×5 IM from 21 to 29d. (term∼31d.), while control 1(C1) received saline (T4↑F serum free T4 from 0.2±0.02 to 0.8±0.1ng/dl†, F plasma glucose from 47±5 to 69±5mg/dl†) Dx at 0.09mg/kg×2 IM on 25 and 26d. was given to M, while control 2(C2) received saline IM. (Dx↑F plasma glucose from 57±5 to 124±12†). In all groups, no change in plasma insulin and IR affinity was noted(p*<.05†<.02,UD=undect.) We conclude: 1) T4 has a trophic effect on FH IR while Dx does not; FB IR being unresponsive. 2) T4 and Dx ↓ FH glycogen content.