Cardiovascular effects of sympathomimetic amines injected into the cerebral ventricles of rabbits

Adrenaline (10–200 μg) and noradrenaline (50 μg) when injected into the lateral cerebral ventricle of pentobarbital-anesthetized rabbits produced a fall in systemic blood pressure, a decrease in spontaneous heart rate and a stimulation of spontaneous respiration. Isoproterenol (50–200 μg) caused a fall in blood pressure and an acceleration of heart rate, whereas phenylephrine (200 μg) caused a slight rise in blood pressure in association with a decrease in heart rate. The hypotension and bradycardia induced by adrenaline were not significantly affected by bilateral vagotomy. Pretreatment of rabbits with intravenous reserpine reversed the adrenaline-induced hypotension to a hypertension and abolished the bradycardia induced, but did not affect the respiratory stimulation. The cardiovascular responses to intraventricular adrenaline were abolished by transection of the spinal cord. In unanesthetized rabbits adrenaline produced presser and cardio-stimulatory effects followed by depressor and cardio-inhibitory effects. These findings would suggest a centrally mediated hypotensive action of adrenaline in anesthetized rabbits but a hypertensive action in unanesthetized rabbits. Furthermore, changes in the cardiac function might be associated with changes in local blood flow, as postulated byKanekoet al. (1960).