Cardiovascular responses to central catecholamines of sinoaortic denervated rats

The characteristic movement-related arterial pressure dips seen in sinoaortic-denervated (SAD) animals suggested they should have enhanced vasodepressor responses to central adrenergic agonists. This was tested by comparing the reductions in mean arterial pressure and heart rate of conscious sham-operated (SO) and SAD rats during injections of norepinephrine (NE) or epinephrine (E) (0.25--16 micrograms) into the fourth cerebral ventricle. NE produced significantly greater maximum vasodepression and, simultaneously, significantly less bradycardia in SAD than SO rats. E, like NE, produced significantly more vasodepression in SADs, but unlike NE, elicited the same magnitude of bradycardia in both groups. The pressures were reduced and the log-dose pressure response curves shifted to the left in SAD rats. These results provide indirect evidence that central sensitivity to intracerebroventricular catecholamines is altered in SAD rats and that the direction of change in sensitivity is divergent for pressure and heart rate.