Sympathetic Control of Canine Abdominal Aorta

Abstract

In anesthetized dogs the peripheral ends of the cut sympathetic chains (LGi-LG 2 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.diameter. Particularly, the range of sympathetic control of the diameter of the aorta was investigated and the functional peculiarities of the bilateral innervation were examined. In addition, the response to sympathetic stimulation along the abdominal aorta was monitored. Finally, to explain the established differences in responsiveness, both pharmacological experiments and histochemical studies were performed. MethodsExperiments were performed on 32 adult mongrel dogs of either sex weighing 11.0-19.0 kg. The dogs were anesthetized with sodium thiopental (10-15 mg/kg, iv) at the beginning of the experiment, and supplementary doses (4-7 mg/kg) were given hourly.To minimize blood losses all surgery was performed with electrocautery. After opening the abdomen with a midline incision from the xiphoid process down to the symphysis, the intestines were drawn to the left side and covered with warmed wet cotton.In 16 dogs the aorta was left intact and normally tethered except at the site where diameter was registered; at this site it was freed for a distance not longer than 5 mm. In all dogs the diameter was recorded 15-20 mm above the iliac bifurcation closely distal to the origin of the caudal mesenteric artery; the cross section of the aorta is circular at this point. In 6 dogs diameter and pressure were monitored at three sites, Site 1 was 15-20 mm above the iliac bifurcation,

Effects of neural stimuli on blood flow through vasa vasorum in dogs.

“…This possibility was examined by measuring the aortic diameter during sympathetic stimulation. Gerova et al (1973) found that, when increases in arterial pressure were prevented, sympathetic stimulation reduced the diameter of the distal abdominal aorta by 8% but did not constrict the proximal abdominal aorta. We found that stellate stimulation did not produce detectable changes in diameter of the thoracic aorta unless arterial pressure changed.…”

Effects of age on aortic pressure-diameter and elastic stiffness-stress relationships in unanesthetized sheep.

“…The major fraction of prior work on aortic elastic properties has been performed on excised vessels or vessel strips (Bergel, 1972;McDonald, 1974;Roach and Burton, 1959;Learoyd and Taylor, 1966;Roach, 1970;Berry et al, 1975;Cox et al, 1976;Alexander, 1954;Vatner and Braunwald, 1975), or in anesthetized animals (Bergel, 1972;McDonald, 1974;Pieper and Paul, 1969;Aars, 1971;Nicolosi and Pieper, 1971;Pagani et al, 1975;Patel and Vaishnav, 1972;Gow, 1972;Gow and Taylor, 1968;Cox, 1975;Gow, 1970;Alexander, 1954;Wiggers and Wegria, 1938;Peterson et al, 1960;Patel et al, 1961;Remington, 1962;Gerova et al, 1973). In 1972, Gow noted that "new techniques are required to produce a continuous monitor of vascular dimensions in conscious animals, thus allowing the precise measurement of the normal physiological variations in vascular calibre and viscoelastic properties."…”

The elasticity of canine and human coronary arteries with reference to postmortem changes.

“…Its spring resistance has 10~2 N at an opening of 0.46 cm. Since this load was distributed over the length of the feet (0.5 cm), the interference to normal diameter pulsation would be negligible (Gerova et al, 1973). The frequency response of the caliper was tested by holding one leg and attaching the other to a mechanical oscillator driven by a servomotor.…”