Cardiovascular responses to adrenergic agonists in sinoaortic denervated rats

1. The cardiovascular effects of systemic alpha and beta adrenergic stimulation were studied in conscious sham-operated and sinoaortic denervated (SAD) rats, 7 days after the corresponding operation. 2. SAD does not modify the pressor response to phenylephrine (0.125-8 micrograms.kg-1, i.v.). The blood pressure increase was compensated for bradycardia in the sham-operated rats but not in the SAD. Only 8 micrograms.kg-1 of phenylephrine induced a slight fall of heart rate in the denervated animals. 3. The beta adrenergic agonist isoproterenol (7.8 ng.kg-1-2 micrograms.kg-1, i.v.) showed a greater hypotensive and a lesser tachycardic action in SAD than in sham-operated rats. However, these differences disappeared after autonomic ganglionic blockade (hexamethonium, 10 mg.kg-1, i.v.). 4. Our results suggest that after 7 days of SAD the pressor response to alpha adrenergic agonists may be unaltered and that the differences in the cardiovascular beta adrenergic response of SAD rats may be due to loss of the baroreflex mechanisms of cardiovascular compensation.