EFFECTS OF BARORECEPTOR REFLEX ON EFFERENT PULMONARY SYMPATHETIC-NERVE ACTIVITY IN ANESTHETIZED CAT

We analyzed the baroceptor reflex effect on efferent pulmonary sympath etic nerve activity (PSNA) in anesthetized cats. PSNA was recorded fro m the central end of the cut nerve bundle, which was isolated from the lobar artery supplying the diaphragmatic lobe. Renal sympathetic nerv e activity (RSNA) and aortic blood pressure (AP) were also simultaneou sly measured. There were grouped discharges synchronous with cardiac c ycle and its respiratory modulation in PSNA. In a given cardiac cycle, the discharge patterns differed between the pulmonary and renal nerve s. Average sympathetic nerve activity and AP obtained from 100 consecu tive cardiac cycles showed that the baroceptor reflex delay time on th e pulmonary nerve (266 ms) was longer than that on the renal nerve (19 5 ms). The data indicate nonuniformity in the cardiac-related PSNA and RSNA. The grouped PSNA disappeared with hexamethonium bromide, indica ting that PSNA originates from postganglionic efferent fibers. To exam ine the baroreflex response of PSNA, AP was increased by 70 mmHg with phenylephrine and decreased by 70 mmHg with nitroprusside. PSNA change d inversely to the changes in mean aortic pressure (MAP). In the Delta MAP-Delta PSNA curve, Delta PSNA reached the maximum level (74%) and the noise level at -56 +/- 4 and 58 +/- 4 mmHg, respectively. The mean slope of the curve was 1.5 +/- 0.1%/mmHg. RSNA also responded inverse ly to the MAP change. However, the mean slope of Delta MAP-Delta RSNA (1.1 +/- 0.1%/mmHg) was significantly smaller than that of the Delta M AP-Delta PSNA curve, and the mean Delta MAP at which RSNA reached the noise level (68 +/- 4 mmHg) was significantly larger than that of PSNA . The data indicate that the baroreflex effect on PSNA is significantl y larger than that on RSNA.