Differential regional sympathetic responses to somatic stimulation in anesthetized dogs

The present study was designed to determine whether regional differences exist in sympathetic responses to somatic nerve stimulation and whether the baroreceptor reflex modulates this somato-sympathetic reflex. The cardiac (CNA), renal (RNA), hepatic (HNA), splenic (SpNA) and adrenal (AdNA) sympathetic postganglionic nerve activities (SNA) were simultaneously recorded in anesthetized dogs with intact (n = 7) or bilaterally sectioned (n = 8) carotid sinus and vagus nerves. In the intact group, electrical stimulation of the left peroneal nerve at low intensity and low frequency (5 V, 5 Hz) produced a fall in mean arterial pressure (MAP) (-9.7 +/- 2.7 mmHg) and a decrease in each SNA with no regional 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, stimulation 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 quantitative 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 stimulated. The changes in SNA (delta SNA) at 10 s after the start of stimulation were plotted as a function of the changes in MAP (delta MAP) and the regression curves were determined. The best fit regression curve 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 significantly smaller in the intact group than in the denervated group. In conclusion, there are regional differences of sympathetic response during the somato pressor response but not during somato depressor response. The baroreceptor reflex may suppress the somato-sympathetic reflex of RNA and AdNA.