Quantitative changes in regional cerebral blood flow of rats induced by alpha‐and beta‐adrenergic stimulants

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Abstract
Cerebral blood flow was measured with the 14C‐ethanol technique in 8 regions (frontal, parieto‐temporal and occipital cortex, caudate nucleus, thalamus, cerebellum, mesencephalon, and pons) of rats. The highest flow values (83–89.5 ml/100 g/min) were found in cortical areas, whereas pons had the lowest flow (48 ml/100 g/min). Intravenous infusion of noradrenaline or adrenaline markedly reduced rCBF (by 22–48% of control levels) in all regions except thalamus, mesencephalon, and pons. The noradrenaline‐induced reduction was blocked, and the effect of adrenaline reversed, after pretreatment with the alpha‐receptor antagonist, phentolamine. Isoprenaline infusion markedly augmented rCBF in thalamus, mesencephalon, pons, and also in the caudate nucleus. The response was reduced by the beta‐receptor antagonist, propranolol. The experiments show the presence and heterogenous distribution in the cerebrovascular bed of alpha‐and beta‐adrenoceptors that can be activated by sympathomimetics given systematically. If noradrenaline was allowed to pass the blood‐brain barrier after osmotic opening with urea, an increased regional flow was obtained, probably due to a mechanism where the vasodilator effect secondary to activation of cerebral metabolism predominated over the direct vasoconstrictor effect of the amine.