Centrally inhibitory effect of adrenaline on cardiovascular and sympathetic nerve system in urethane anesthetized rat

The present study was undertaken to determine the central effect of adrenaline. Adrenaline was administered to the cisterna magna in urethane anesthetized rats. Following the intracisternal injections, the blood pressure dropped and reached a plateau after 15 min, the hypotensive effect continuing for at least 30 min. The heart rate also slowed concomitantly with the depressor effect. The vehicle treated rats did not show any cardiovascular responses. The cardiovascular responses in the experimental rats were accompanied by an inhibition of the sympathetic nerve activity. Pressor responses to electrical stimulation of the posterior hypothalamus were partly inhibited, while pressor responses to intravenous injections of noradrenaline remained unchanged. In DOCA hypertensive rats, the depressor responses to intracisternal injections of adrenaline were augmented. These findings suggest that adrenaline in the brain could contribute to the inhibitory mechanism of the cardiovascular system accompanied by inhibition of the sympathetic nerve system, and that this mechanism may be attenuated in DOCA hypertensive rats.