• B Malinowska, G Godlewski, W Buczko, and M Göthert.
• Zaklad Farmakodynamiki, Akademia Medyezna, Bialystok, Poland.
• Eur. J. Pharmacol. 1996 Nov 14; 315 (2): 159-64.

AbstractThe influence of substance P 3 (microgram/kg) and (+)-tubocurarine (850 micrograms/kg) on the Bezold-Jarisch reflex in urethane-anaesthetized rats was studied. The Bezold-Jarisch reflex was induced by the 5-HT3 receptor agonist phenylbiguanide (0.3, 1, 3 and 10 micrograms/kg i.v.) and by capsaicin (10 micrograms/kg i.v.). The 5-HT3 receptor antagonist ondansetron (10 micrograms/kg) abolished the phenylbiguanide- but not the capsaicin-stimulated bradycardia, indicating that phenylbiguanide and capsaicin act via different trigger mechanisms (5-HT3 receptor-dependent and -independent, respectively). Substance P significantly potentiated the phenylbiguanide- but not the capsaicin-induced decrease in heart rate. Also, when the phenylbiguanide-induced response was amplified by substance P, it was abolished by ondansetron. (+)-Tubocurarine inhibited the phenylbiguanide-induced bradycardia, but did not affect the capsaicin-stimulated decrease in heart rate. Our results demonstrate that substance P potentiates but (+)-tubocurarine inhibits the 5-HT3 receptor-mediated Bezold-Jarisch reflex. Both effects are probably due to direct influences of the drugs on the 5-HT3 receptors on sensory vagal nerves in the heart.

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