Enhanced adrenergic response of the cerebral vasculature in alloxan-induced diabetic rats.

The influence of alloxan-induced diabetes on the adrenergic constriction of the rat cerebral vasculature was investigated in the in situ perfused brain preparation. The preparation was perfused with an artificial medium at a constant flow rate and the change in perfusion pressure was measured. Norepinephrine (NE) and serotonin produced a dose-dependent increase in the perfusion pressure, but only the effect of NE was significantly enhanced in the diabetic rats. Such an enhancement of NE-induced vasoconstriction was not observed in the perfused hindquarter preparations from the diabetic rats. Propranolol (1 microM) potentiated the cerebrovascular constriction by NE and abolished the difference between diabetic and control rats at low doses of NE. However, vasoconstriction by the higher doses of NE in the diabetic rats was still enhanced even in the presence of propranolol. The cerebrovascular constriction by phenylephrine was also enhanced in the diabetic rats, while the vasoconstricting effects of clonidine, xylazine and oxymetazoline were not affected by diabetes. These results suggest that the enhanced cerebrovascular constriction by NE may be due to either the reduced response through beta-adrenoceptors or the enhanced response through alpha 1-adrenoceptors. The enhanced adrenergic constriction of the cerebral vasculature might be concerned with the high incidence of neurological deficit in stroke patients with diabetes.