HYPERGLYCEMIA MODIFIES THE REACTION OF MICROVESSELS TO INSULIN IN RATSKELETAL-MUSCLE

The role played by glucose and/or insulin in local vascular regulation of tissue glucose uptake is largely unknown. Thus, the aim of this st udy was to examine microvascular changes induced either by hyperinsuli naemia alone or in combination with hyperglyaemia. The effects of insu lin or glucose on the diameter and periodic vasomotion of precapillary arterioles (diameter < 20 mu m) were determined by using the spinotra pezius muscle preparation in fasted, anaesthetized rats. Ten minutes a fter s.c. insulin administration, the blood insulin level was greatly increased whereas plasma glucose remained unchanged, This was associat ed with a marked and durable vasodilation of terminal arterioles witho ut significant changes in vasomotion. When similar plasma insulin leve ls were attained 64 glucose infusion, tissue glucose uptake was increa sed in spite of a partial constriction and increased vasomotion of pre capillary arterioles. Importantly, local tissue blood flow was not red uced despite the diminution in microvascular diameters. These results indicate that hyperinsulinaemia alone produces an increase in the diam eter of terminal arterioles. This effect seems to be offset when the s ame level of hyperinsulinaemia is associated with hyperglycaemia (such as occurs postprandially), as illustrated by vasoconstriction of the muscle terminal arterioles. Our data suggest that the vasoconstriction of precapillary arterioles may be part of an active regulation for op timal glucose supply to the tissue in acute hypoglycaemic episodes. Th ese data provide the first direct evidence that insulin and glucose ca n act as regulators of microflow in the skeletal muscle, as illustrate d by changes in precapillary haemodynamics.