Regulation of glucose homeostasis in rat jejunum by despentapeptide-insulin in vitro.

The regulation of the absorption and metabolism of glucose in rat small intestine by insulin was studied by the perfusion of isolated loops of proximal jejunum in vitro. The addition of an active, monomeric form of insulin, despentapeptide-insulin, to the serosal side of the intestine from normal rats inhibited luminal glucose absorption (421 (11) to 285 (11) mumol/h/g dry wt, p less than 0.001) and lactate production (340 (28) to 192 (26) mumol/h/g dry wt, p less than 0.001), but had no effect on glucose utilisation (231 (11) and 210 (16) mumol/h/g dry wt). The production of acute insulin deficiency by the injection of anti-insulin serum in vivo caused a marked inhibition of luminal glucose absorption (421 (11) to 240 (13) mumol/h/g dry wt, p less than 0.001), glucose utilisation (231 (11) to 48 (2) mumol/h/g dry wt, p less than 0.001) and lactate production (340 (28) to 94 (2) mumol/h/g dry wt, p less than 0.001) in vitro. The effects of insulin deficiency were reversed by despentapeptide-insulin in vitro, so that the rates of absorption and metabolism for intestine from insulin deficient and normal rats were similar in the presence of the modified insulin. All the effects caused by insulin deficiency and despentapeptide-insulin were apparent within minutes and could not be attributed to hyperglycaemia. It is concluded that rat small intestine is subject to rapid and direct regulation by insulin.