Femoral arterial diameter and pressure were measured in anesthetized dogs. Immediately after section of the ipsilateral lumbar sympathetic chain the artery dilated, reaching a maximum of 122.0% (±0.56 SEM) of resting diameter within 30 to 40 seconds. Later the diameter diminished, stabilizing at 104.3% (±1.8 SEM) of resting diameter within 15 minutes. Stimulation of the peripheral stump of the sympathetic chain induced frequency-dependent constriction, the frequency-response curve being hyperbolic. The average maximal response was 13.42% (± 1.19 SEM) of the resting diameter. These changes were not dependent on suprarenal secretion, blood flow, or changes in distal vascular bed resistance. The contraction of the artery was slow. The half-time of stabilized contraction was 21.6 seconds at a stimulus frequency of 1/sec and 36.8 seconds at 25/sec. The half-time of relaxation was shorter (10.7 seconds and 21.5 seconds, respectively) and also frequency-dependent. A significant dilatation, after stimulation, inversely proportional to the stimulation frequency, occurred after low-frequency stimulations. The time course of contraction suggests the activation of individual smooth muscle layers successively more remote to the nerve endings, possibly due to diffusion of transmitter liberated at the nerve endings by stimulation.From the Department of Cardiovascular Physiology, Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava..
The diameter of a major coronary artery, the ramus interventricularis ventralis (RIV), was measured in dogs with arrested hearts perfused by an extracorporeal circulation. The resting diastolic diameter was 1.78 +/- 0.07 mm (mean +/- SE) at a diastolic pressure of 74.2 +/- 3.4 mm Hg. Bilateral supramaximal stimulation of fibers leaving the cranial pole of the stellate ganglion decreased the diameter by 71.2 +/- 8.9 micrometer, i.e., 4.0 +/- 0.5% of the resting diameter. Stimulation of the left stellate ganglion contributed 59.8 +/- 5.7% of the maximum response; that of the right contributed 40.3 +/- 5.5%. Stimulation of the thoracic ganglia (T2-4) resulted in a 1.2 +/- 0.4% decrease in coronary vessel diameter. RIV failed to respond to bilateral caudal cervical ganglion stimulation. After iv administration of phentolamine, 1-2 mg/kg, no response to sympathetic stimulation could be elicited. Therefore, it appears that alpha-receptors are activated by the release of the sympathetic neurotransmitter to sympathetic stimulation and that beta-receptors are not involved in the response of RIV to sympathetic stimulation.
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,
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