Effect of verapamil on cardiac chronotropic response to vagal stimulation in neonatal pigs.
The effects of verapamil on the chronotropic response to vagal stimulation in young pigs anesthetized with sodium pentobarbital (30 mg/kg of body weight, intraperitoneally) was evaluated. After bilateral vagotomy, the administration of verapamil (loading dose of 100 micrograms/kg, followed by 2 micrograms/kg/min infusion) resulted in a significant (P less than 0.05) reduction in heart rate (HR) and mean arterial blood pressure. Cardiac frequency responses to vagal stimulation were obtained by stimulating the distal end of the right vagus nerve at selected frequencies (5, 10, 15, and 20 Hz) with supramaximal voltage (10 to 15 V) and constant duration (2 ms). The HR was measured after 15 s at each level of stimulation. The slopes of decrease in HR to the frequency of vagal stimulation were significantly (P less than 0.05) reduced after verapamil as compared with its controls. After atropine (0.5 mg/kg), the vagally induced tachycardia was partially attenuated by verapamil, but was completely eliminated by beta blockade with propranolol (1 mg/kg). These findings indicated that verapamil may influence the parasympathetic control of the heart in young pigs.
D000818:Animals; D000831:Animals, Newborn; D001285:Atropine / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D011433:Propranolol / Q000494:pharmacology; D013552:Swine / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*; D014700:Verapamil / Q000494:pharmacology*
D001285:Atropine; D011433:Propranolol; D014700:Verapamil