The response of adipose tissue blood flow to insulin-induced hypoglycemia in conscious dogs and rats.

A comparative study, focusing on the modification of regional blood flow in adipose tissue during insulin-induced hypoglycemia, was performed on dogs and rats at room temperature (22 degrees C) and on rats at thermoneutrality (28-32 degrees C). Insulin dosages of 3 IU/kg in rats and 0.75 IU/kg in dogs were found to cause changes of comparable amplitude and kinetics in plasma glucose and catecholamine levels in both species. At thermoneutrality, hypoglycemia induced an increase in blood supply to adipose tissue in both species: in dogs, blood flow density was markedly increased from the periphery (+75% in subcutaneous region) to the deeper locations (+550% in perirenal region); in rats, the increase of fractional cardiac output was especially pronounced in brown adipose tissue. By contrast, in rats acclimated at room temperature, hypoglycemia induced a decrease of fractional cardiac output to white adipose tissue and even more markedly, to brown adipose tissue (-45%). These results strongly suggest that, in rats at ambient temperature below thermoneutrality, thermoregulatory heat production is shut off during hypoglycemia.