CO2-dependent component of the neurogenic vascular tone in the cat

Abstract

Complete vascular isolation of the hindlimbs was performed in vagotomized cats under Sodium Pentobarbital anesthesia. The hindlimbs were perfused at constant flow with blood kept at a constant and physiological\(P_{0_2 }\),\(P_{{\text{C}}0_2 }\), and pH values by means of a specially designed pump-oxygenator system. The animals were hyperventilated with different CO₂ mixtures (0%, 5%, 7% and 10% in O₂) thereby changing blood gases and pH levels in the upper body but not in the hindlimb vascular bed. At body\(P_{{\text{aC}}0_2 }\) (mm Hg) of 13.7 ±1.0 (means±SE), 30.6±1.05, 40,4±0,9 and 58.4 ±2.9 the hindlimb perfusion pressure (mm Hg) was, respectively 124±7.6, 138±7.4, 156±11.9 and 187 ±15.1. These changes in perfusion pressure were still present after complete peripheral chemoreceptor denervation but were abolished after section of the spinal cord at the T₅ level. Since hindlimb perfusion pressure fell when body\(P_{{\text{aC}}0_2 }\) was lowered below physiological levels it is concluded that part of the neurogenic vascular tone of the hindlimbs is maintained by a CO₂ mediated stimulation of supraspinal structures.