Cardiovascular responses to cholinergic agonists in sinoaortic denervated rats

1. The cardiovascular effect of systemic nicotinic and muscarinic cholinergic stimulation were studied in conscious sham operated and sinoaortic denervated (SAD) rats, 7 days after the corresponding operation. 2. The administration of the nicotinic ganglionic agent, 1,1-dimethyl-4-phenylpiperazinium (DMPP, 50-100 micrograms.kg-1, i.v.) induced a fall of heart rate that was significantly higher in SAD rats than in sham rats. DMPP induced in sham rats an increase of arterial pressure but in SAD animals a biphasic response: an initial hypotension followed by an increase of arterial pressure. 3. Under muscarinic blockade, DMPP only showed a pressor and tachycardic action in both groups of rats without differences between them. 4. The muscarinic agonist, carbachol (0.1-10 micrograms.kg-1, i.v.) showed the same hypotensive and bradycardic action in both groups of rats. 5. Our results suggest that after 7 days of SAD, differences in the response to DMPP between sham and denervated animals could be due to the loss of baroreflex mechanisms. The increased bradycardic effect of DMPP in SAD rats could be mediated by a supersensitivity of parasympathetic ganglionic nicotinic receptors, whilst the sympathetic ganglionic nicotinic receptors remained unaltered. On the other side, the cardiovascular muscarinic responses to carbachol remain unaffected in SAD rats.