ADRENOCEPTORS IN INTRACEREBRAL RESISTANCE VESSELS

Abstract

1 The effects of tyramine and isoprenaline on hypothalamic blood flow (HBF) were measured in conscious rabbits. 2 Injections of small doses of tyramine caused an increase in HBF while larger doses caused a decrease in HBF. 3 Isoprenaline injections also produced an increase in HBF. 4 The vasodilatation induced by isoprenaline and the small dose of tyramine was blocked by propranolol. 5 The vasoconstriction induced by the larger doses of tyramine was abolished by phenoxybenzamine. 6 Chemical sympathectomy of the hypothalamus with 6‐hydroxydopamine and depletion of biogenic amines by reserpine also abolished tyramine‐induced vasoconstriction. 7 These results suggest the presence of α‐ and β‐adrenoceptors in cerebral resistance vessels, and that these receptors may be activated by released (endogenous) noradrenaline.