CARDIOVASCULAR-RESPONSES TO CHOLINERGIC AGONISTS IN SINOAORTIC DENERVATED RATS

1. The cardiovascular effect of systemic nicotinic and muscarinic chol inergic stimulation were studied in conscious sham operated and sinoao rtic 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 mug.kg-1, i.v.) induced a fall of he art 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 inc rease of arterial pressure. 3. Under muscarinic blockade, DMPP only sh owed a pressor and tachycardic action in both groups of rats without d ifferences between them. 4. The muscarinic agonist, carbachol (0.1-10 mug.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 animal s could be due to the loss of baroreflex mechanisms. The increased bra dycardic effect of DMPP in SAD rats could be mediated by a supersensit ivity of parasympathetic ganglionic nicotinic receptors, whilst the sy mpathetic ganglionic nicotinic receptors remained unaltered. On the ot her side, the cardiovascular muscarinic responses to carbachol remain unaffected in SAD rats.