CENTRAL α‐ AND β‐ADRENOCEPTORS MODIFYING ARTERIAL BLOOD PRESSURE AND HEART RATE IN CONSCIOUS CATS

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Abstract
In conscious unrestrained cats noradrenaline, α‐methylnoradrenaline and clonidine, infused into the lateral cerebral ventricles (i.c.v.) caused dose‐related falls in blood pressure and heart rate; both effects were abolished after i.c.v. phentolamine. In 12 out of 20 cats, i.c.v. isoprenaline and salbutamol when given caused dose‐related pressor responses and tachycardias. These effects were abolished after i.c.v. β‐adrenoceptor blocking drugs but were unaffected by α‐adrenoceptor blocking agents. In 5 out of 20 cats, i.c.v. isoprenaline regularly produced dose‐related falls in blood pressure with associated tachycardias; both effects were abolished after i.c.v. β‐adrenoceptor blocking agents. Intracerebroventricular dopamine produced cardiovascular responses which were qualitatively similar to those produced by i.c.v. isoprenaline. Intracerebroventricular adrenaline produced complex responses in untreated animals but typical α‐effects were obtained after prior i.c.v. treatment with a β‐adrenoceptor blocking agent and typical β‐effects after i.c.v. pretreatment with an α‐adrenoceptor blocking agent. The cardiovascular changes produced by i.c.v. β‐adrenoceptor agonists were abolished after systemic administration of hexamethonium or bethanidine. The results are discussed in the light of the mode of action of β‐adrenoceptor stimulants and β‐adrenoceptor blocking agents in the treatment of hypertension.