Role of the heart and peripheral resistance in the reflex effect of group I afferent fibers on blood pressure.
Experiments were done on anesthetized and curarized cats to see whether the increase in blood pressure caused by electrical stimulation of group I afferent fibers is related to a direct reflex effect on the heart. The reflex effect of electrical stimulation of group I afferent fibers from the gastrocnemius-soleus muscles on the arterial pressure, the left ventricular pressure, the inotropic state of the left ventricle (dP50/dt) and the heart rate were compared before and after beta-blockade with propranolol (0.1 mg/kg intravenously) to reduce a possible direct effect on the heart. The same comparison was made before and after alpha-blockade with phentolamine (2.5 mg/kg intravenously) to keep the peripheral resistance constant. Electrical stimulation of group I afferent fibers caused an increase in the blood pressure, the left ventricular pressure and, to some extent, the inotropic state of the left ventricle and the heart rate. The beta-blockade had no significant effect on these increases, while the alpha-blockade abolished the increase in blood pressure. It is concluded that the effect of stimulation of group I afferent fibers on the blood pressure is not dependent on a direct reflex effect on the heart, but can be better explained by a reflex increase in the peripheral resistance.
Orani
G P
GP
Institute of Human Physiology, University of Cagliari, Italy.
Decandia
M
M
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D002415:Cats; D004558:Electric Stimulation; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000502:physiology; D009132:Muscles / Q000294:innervation; D009200:Myocardial Contraction / Q000502:physiology; D009412:Nerve Fibers / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D012018:Reflex / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology
D011433:Propranolol; D010646:Phentolamine