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.