CHANGES IN EFFERENT PULMONARY SYMPATHETIC-NERVE ACTIVITY DURING SYSTEMIC HYPOXIA IN ANESTHETIZED CATS

Changes in efferent pulmonary sympathetic nerve activity during system ic hypoxia in anesthetized cats. Am. J. Physiol. 269 (Regulatory Integ rative Comp. Physiol. 38): R1404-R1409, 1995.-Changes in efferent symp athetic nerve activity to the pulmonary vessels during systemic hypoxi a have yet to be elucidated. The purpose of this study was to determin e the pulmonary sympathetic nerve activity (PSNA) changes in response to acute systemic hypo xia before and after sinoaortic denervation plu s vagotomy in anesthetized cats. The denervation was performed to esti mate the central nervous system-mediated peripheral chemoreceptor- and baroreceptor-independent PSNA change. PSNA was recorded from the cent ral end of the cut nerve bundle, which was isolated from the lobar art ery supplying the diaphragmatic lobe. Renal sympathetic nerve activity (RSNA) and systemic and pulmonary arterial pressures were also measur ed simultaneously. The animals were submitted to similar to 3-min peri ods of graded hypoxia (16, 12, 8, 5, and 3% O-2 inhalations). PSNA did not change from normoxia down to an arterial O-2 partial pressure (Pa -o2) of similar to 45 Torr (with 12-21% O-2 inhalations). Below this l evel, PSNA began to increase, and markedly so (similar to 2.5-fold) at a Pa-o2 of similar to 15 Torr (with 3% O-2). The hypoxic PSNA increas e was significantly larger than that for RSNA, with a Pa-o2 of less th an similar to 30 Torr (with 3-8% O-2). Particularly at a Pa-o2 of -sim ilar to 15 Torr, the magnitude of the PSNA increase was two times grea ter than that for RSNA. After denervation, the hypoxic PSNA increase w as significantly attenuated at a Pa-o2 of similar to 25 to similar to 45 Torr (with 5-12% O-2), but the attenuation was very small; therefor e most of the PSNA increase persisted. The hypoxic RSNA increase, in c ontrast, was mostly abolished after denervation. The data indicate tha t the neural reflex effect of systemic hypoxia on PSNA is significantl y greater than that on RSNA and suggest that the hypoxic PSNA increase is mostly mediated by central mechanisms, whereas that for RSNA is ch iefly caused by peripheral chemoreceptors.