Central cardiovascular effects of physostigmine in the cat; possible cholinergic aspects of blood pressure regulation.
The cental actions of the lipophilic cholinesterase inhibitor physostigmine were investigated by infusing very low doses (0.8 micrograms up to 18 micrograms per kg) into the left vertebral artery of the anaesthetized cat. A dose as low as 2.7 micrograms per kg reduced blood pressure by about 35%. High doses caused bradycardia. Occlusion of the right vertebral artery shifted the dose-response curve to the left. It seems likely that the hypotension was due to stimulation of muscarinic receptors in the pontomedullary region, since pretreatment with dexetimide administered via the vertebral artery strongly reduced the effect. Mecamylamine and the adrenergic blocking agents metoprolol and piperoxan, infused into the vertebral artery, could not reduce the depressor response and the bradycardic action. Both bilateral cervical vagatomy and peripherally applied N-methylatropine did not change the hypotensive action of physostigmine. This observation points towards a reduction of sympathetic outflow as the possible cause of the depressor effect. Atenolol, given intravenously, diminished the bradycardia to a great extent, whereas N-methylatropine did not significantly alter the negative chronotropic action of physostigmine. These results suggest a dominant role for the sympathetic system in reducing cardiac frequency. After intravenous administration, only doses higher than 28 micrograms per kg evoked hypotension, which could not be blocked by intravenously administered N-methylatropine. However, centrally infused dexetimide considerably antagonized this effect, indicating that the hypotension was brought about by a central action and not evoked peripherally. Application of the drug via the external carotid arteries resulted in hypotension after considerably higher doses than those following administration via the vertebral artery, indicating the pontomedullary region as the main site of action. It is concluded that the present experimental data obtained with physostigmine support the hypothesis that ACh might have a transmitter role in the central haemodynamic control.
D000109:Acetylcholine / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D001921:Brain / Q000187:drug effects*; D002415:Cats; D003909:Dexetimide / Q000494:pharmacology; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D008297:Male; D018377:Neurotransmitter Agents / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010830:Physostigmine / Q000494:pharmacology*; D014711:Vertebral Artery / Q000502:physiology
D018377:Neurotransmitter Agents; D003909:Dexetimide; D010830:Physostigmine; D000109:Acetylcholine