Cardiovascular responses to cholinergic agonists in sinoaortic denervated rats

Area of Science:

• Cardiovascular Physiology
• Neuropharmacology
• Autonomic Nervous System Research

Background:

• The autonomic nervous system regulates cardiovascular function via nicotinic and muscarinic cholinergic pathways.
• Baroreflex mechanisms are crucial for maintaining blood pressure homeostasis.
• Sinoaortic denervation (SAD) disrupts baroreceptor input, potentially altering autonomic responses.

Purpose of the Study:

• To investigate the cardiovascular effects of systemic nicotinic and muscarinic cholinergic stimulation in rats following sinoaortic denervation (SAD).
• To elucidate the role of baroreflex mechanisms in mediating these cardiovascular responses.
• To assess potential alterations in ganglionic nicotinic and muscarinic receptor sensitivity post-SAD.

Main Methods:

• Conscious sham-operated and SAD rats were studied 7 days post-operation.
• Cardiovascular responses to intravenous administration of the nicotinic agent 1,1-dimethyl-4-phenylpiperazinium (DMPP) were assessed.
• Cardiovascular responses to the muscarinic agonist carbachol were evaluated, with and without muscarinic blockade.

Main Results:

• DMPP induced a greater heart rate fall in SAD rats compared to sham rats.
• DMPP elicited a biphasic arterial pressure response in SAD rats (hypotension followed by hypertension), versus hypertension in sham rats.
• Muscarinic blockade abolished DMPP's hypotensive effect and revealed similar pressor and tachycardic actions in both groups.
• Carbachol produced consistent hypotensive and bradycardic effects in both SAD and sham rats.

Conclusions:

• Loss of baroreflex mechanisms after SAD likely contributes to altered cardiovascular responses to DMPP.
• The enhanced bradycardic effect of DMPP in SAD rats may indicate supersensitivity of parasympathetic ganglionic nicotinic receptors.
• Sympathetic ganglionic nicotinic receptors and cardiovascular muscarinic responses to carbachol appear unaffected by SAD.