Coronary vascular responses to nicotine in the anaesthetized dog.
The effect of the intra-coronary (i.c.) injection of nicotine on large coronary artery diameter and coronary blood flow was examined in anaesthetized dogs. In sixteen untreated dogs nicotine (20 micrograms i.c.) had a biphasic effect on arterial pressure (initial increase, 7 +/- 2 mmHg; secondary decrease, -8 +/- 3 mmHg) which was accompanied by small and variable effects on heart rate and an increase in LV dP/dt. Nicotine increased large coronary artery diameter by 5.8 +/- 0.8% but had a biphasic effect on coronary blood flow (initial increase, 41 +/- 7 ml/min; secondary decrease, -10 +/- 2 ml/min). Bilateral vagotomy or muscarinic receptor blockade with atropine (0.1 mg/kg i.v.) did not significantly affect the nicotine-induced changes in coronary artery diameter or coronary blood flow. The additional antagonism of beta-adrenoceptors with propranolol (1 mg/kg i.v.) abolished the effect of nicotine in coronary artery diameter (delta CD = 0.2 +/- 0.2%) and the initial increase in coronary blood flow (delta CBF = 1 +/- 1 ml/min) but enhanced the secondary decrease in flow (delta CBF = -25 +/- 3 ml/min). The nicotine-induced decrease in coronary blood flow observed after muscarinic and beta-adrenoceptor blockade was attenuated by antagonism of alpha 1-adrenoceptors with prazosin (10 micrograms/kg i.c., delta CBF = -15 +/- 3 ml/min) and abolished after additional antagonism of alpha 2-adrenoceptors with idazoxan (50 micrograms/kg i.c., delta CBF = -2 +/- 1 ml/min). These results indicate that in the anaesthetized dog intra-coronary injection of nicotine results in beta-adrenoceptor mediated dilatation of both large and small coronary arteries.(ABSTRACT TRUNCATED AT 250 WORDS)
Woodman
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Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia.
D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D001285:Atropine / Q000008:administration & dosage / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004285:Dogs; D005260:Female; D007269:Injections, Intra-Arterial; D007275:Injections, Intravenous; D008297:Male; D018727:Muscarinic Antagonists; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology*; D010275:Parasympathetic Nervous System / Q000502:physiology; D011224:Prazosin / Q000008:administration & dosage / Q000494:pharmacology; D011433:Propranolol / Q000008:administration & dosage / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology; D014628:Vagotomy; D014655:Vascular Resistance / Q000187:drug effects
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D018727:Muscarinic Antagonists; D009538:Nicotine; D001285:Atropine; D011433:Propranolol; D011224:Prazosin