INSULIN-INDUCED HYPOGLYCEMIA AND SUGAR-TRANSPORT ACROSS THE BRUSH-BORDER AND BASOLATERAL MEMBRANES OF RAT JEJUNAL ENTEROCYTES

Acute hypoglycaemia enhances intestinal sugar uptake but the mechanisms involved are unknown. Results from the present study show increased galactose movement across the brush border and basolateral membranes of isolated upper, but not mid-villus, jejunal enterocytes 45 min after intravenous administration of insulin to rats at a level which reduced by half plasma glucose concentration. Incubation of upper villus cells from uninjected animals with insulin (100 mU ml-1) for 40 min was without effect on brush border or basolateral sugar transport. Insulin treatment of rats did not affect glucose uptake by brush border vesicles prepared from upper villus cells when the process was driven by an inwardly directed 100 mM sodium thiocyanate gradient. In contrast, glucose uptake using a 100 mM inwardly directed sodium chloride gradient was reduced by 49% following hypoglycaemia. It is concluded that the enhanced sugar uptake following insulin hypoglycaemia involves both brush border and basolateral membranes of only the most mature villus cells at the villus tip. Upregulation of Na+-sugar cotransport at the brush border is best explained by an increased electrochemical driving force for Na+-sugar cotransport rather than increased numbers of transporters. The transport response is not due to a direct effect of insulin on the enterocyte and the possible systemic factors involved are discussed.