Sympathetic Control of Canine Abdominal Aorta

In anesthetized dogs the peripheral ends of the cut sympathetic chains (LG1-LG2 level) were stimulated while blood pressure was held constant artificially, and the diameter of the abdominal aorta was monitored. Bilateral stimulation induced a reduction in diameter that was directly related to the stimulation frequency. Maximal diameter reduction of the aorta above the iliac bifurcation averaged 8.01±0.74% of resting diameter. The half-time of contraction (36.5±2.1 to 51.5±3.6 seconds) was indirectly related to the stimulation frequency. The effects of right or left sympathetic chain stimulation were quantitatively similar to each other (51.3±4.4% and 46.7±4.5%, respectively), and the response to bilateral stimulation (92.8±6.1%) did not differ from the calculated value for paired unilateral stimulation (100%). A significant proximo-distal gradient of response (below the branching off of the renal arteries 2.97±0.28%, at the midpoint 5.15±0.52%, and above the iliac bifurcation 8.56±0.79% of resting diameter) along the abdominal aorta was established during bilateral stimulation. Histochemical examination showed no corresponding differences in the density or the distribution of monoaminergic terminals. Dose-response relations for spiral strips taken from analogous aortic segments, however, displayed sensitivity to norepinephrine in the same order as the gradient in the in vivo experiments.