Catecholamines potentiate the effect of thyroid hormone on intestinal absorption of glucose in the rat

The study is to investigate the role of catecholamines on the increased absorption of glucose from the gut by thyroxine, the effect of graded doses of adrenaline and noradrenaline on glucose absorption was studied in euthyroid (ET), hyperthyroid (TH-) and hypothyroid rats (Thx). Glucose absorption was deduced in vivo from intestinal segment perfused with Kreb's bicarbonate solution containing 5.6 mM glucose and in vitro using the everted sac technique. In vivo, basal glucose absorption was significantly increased in the hyperthyroid and decreased in the hypothyroid rats (1.97 +/- 0.19 mM/g, P<0.01, and 0.92 +/- 0.10 mM/g, p<0.05 respectively) when compared with the euthyroid group (1.34 +/- 0.15 mM/g). Adrenaline (20 mg/dl - 80 mg/dl) increased glucose absorption in a dose dependent manner in all the groups. However, the responsiveness of the gut glucose absorption to adrenaline (as evidenced by the dose producing half- maximal absorption or ED50) was reduced by thyroidectomy (ED50 = 26.09 mg/100 ml) and increased by chronic thyroxine treatment (ED50 = 11.13 mg/100 ml). The ED50 in the euthyroid animals was 14.6 mg/100 ml. In vitro, glucose absorption from the isolated segments in both Thx and TH- rats were significantly reduced (P<0.05). Incubation of the isolated intestinal segments with graded doses of adrenaline caused a significan and dose related increases in glucose absorption. However thyroidectomy shifted the dose-response curve for glucose uptake from the isolated intestinal sac incubated with adrenaline to the right of the curve for euthyroid rats. It is concluded that catecholamines may play a role in the increase in intestinal absorption by thyroid hormones.