DIFFERENTIAL REGIONAL SYMPATHETIC RESPONSES TO SOMATIC STIMULATION INANESTHETIZED DOGS

The present study was designed to determine whether regional differenc es exist in sympathetic responses to somatic nerve stimulation and whe ther the baroreceptor reflex modulates this somato-sympathetic reflex. The cardiac (CNA), renal (RNA), hepatic (HNA), splenic (SpNA) and adr enal (AdNA) sympathetic postganglionic nerve activities (SNA) were sim ultaneously recorded in anesthetized dogs with intact (n = 7) or bilat erally sectioned (n = 8) carotid sinus and vagus nerves. In the intact group, electrical stimulation of the left peroneal nerve at low inten sity and low frequency (5 V, 5 Hz) produced a fall in mean arterial pr essure (MAP) (-9.7 +/- 2.7 mmHg) and a decrease in each SNA with no re gional differences RNA (79.2 +/- 8.5%), AdNA (82.7 +/- 5.4%), HNA (89. 4 +/- 4.5%), CNA (87.5 +/- 3.5%), SpNA (84.2 +/- 3.2%). In contrast, s timulation at high intensity and high frequency (25 V, 50 Hz) produced a rise in MAP (+21.4 +/- 3.8 mmHg) and increases in SNA with quantita tive predominance of RNA (178.6 +/- 13.6%) and AdNA (158.3 +/- 16.1%) over HNA (129.0 +/- 4.2%), CNA (117.7 +/- 7.6%), and SpNA (112.0 +/- 6 .2%). Similar responses were observed when the left ulnar nerve was st imulated. The changes in SNA (Delta SNA) at 10 s after the start of st imulation were plotted as a function of the changes in MAP (Delta MAP) and the regression curves were determined. The best fit regression cu rve was a logistic sigmoid curve in the intact group and a linear one in the baroreceptor denervated group. Furthermore, Delta RNA/Delta MAP and Delta AdNA/Delta MAP during the somato-pressor response were sign ificantly smaller in the intact group than in the denervated group. In conclusion, there are regional differences of sympathetic response du ring the somato pressor response but not during somato depressor respo nse. The baroreceptor reflex may suppress the somato-sympathetic refle x of RNA and ANA.