A possible dual role of noradrenaline in cardiovascular responses mediated by the central nervous system

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Abstract
The cardiovascular responses induced by intraven-tricular noradrenaline after intraventricular pretreatment with reserpine, imipramine, and chlorpromazine were studied in cats anesthetized with chloralose and under artificial respiration. Pretreatment with all three agents produced various degrees of "reversal" of the usual cardiovascular depressant responses to noradrenaline (50 jig intraventricularly), leading to significant pressor responses and tachycardia. These sympathetic excitatory cardiovascular responses were significantly reduced by spinal C-2 section. It is suggested that this reversal phenomenon is not due entirely to brain noradrenaline depletion, but that all three agents (reserpine, imipramine, and chlorpromazine) act by blocking neuronal uptake of noradrenaline, thereby preventing the usual central cardiovascular inhibitory effects of the amine. These findings also suggest a possible dual role of noradrenaline in cardiovascular changes mediated by the central nervous system.