PULMONARY CHEMOREFLEX AND PHRENIC SYMPATHETIC EFFERENTS

The pulmonary chemoreflex components such as reactions of phrenic symp athetic neuron (PhSN) activity, phrenic nerve activity, heart rate and blood pressure were tested in chloralose-anesthetized, paralyzed cats . 10 mug to 160 mug phenylbiguanide (PBG) in 0.9% NaCl was injected in to the pulmonary circulation. PBG injected into the right atrium (in 1 1 of 19 experiments) and into the pulmonary artery (in 5 of 8 experime nts), evoked short-latency (1-1.4 sec) dose-dependent increase in PhSN activity accompanied by increase in blood pressure, and followed by d ecrease in these two variables. In all experiments, activity of the ph renic nerve was depressed, and bradycardia occurred after PBG injectio n. All responses to PBG injections into the pulmonary artery were abol ished following bilateral vagotomy. In the same procedure related to t he right atrium after vagotomy, the increases in PhSN activity and blo od pressure were also abolished, although a decrease in heart rate, Ph SN activity and in the amplitude of phrenic nerve discharges together with an increase in their frequency persisted. Our results suggest tha t short-latency increase in PhSN activity is a component of pulmonary chemoreflex.