Reflex Regulation of Smooth Muscle Tone of Conduit Vessel

140

Diameters of the exposed femoral artery of anesthetized dogs were continuously measured with ultrasonic elements of lead zirconate titanate. In 13 of 16 dogs vascular diameters increased following a sudden increment in arterial blood flow induced by the injection of vasodilat i ng agents (acetylcholine, histamine) peripheral to the recording level, by opening an arteriovenous shunt, or after tetanic stimulation of die sciatic nerve. The dilatation response occurred despite slight reductions in femoral blood pressure, and was present after ganglionic blockade, blockade of alpha and beta receptors with phenoxybenzamine and propranolol, atropinization and injection of an antihistamine. The dilatation response was also observed after transsection of the femoral artery distal to the recording level and is therefore not dependent on the retrograde propagation of nervous or myogenous impulses along the vascular wall. ADDITIONAL KEY WORDSarterial diameter arterial smooth muscle arteries autorcgulation blood circulation blood pressure ultrasonic vasodilator agents vasomotor system• A conduit vessel, such as the femoral artery, varies in diameter with blood pressure (1). If this were the only mode of regulation, an increase in blood flow induced by arteriolar dilatation would result in an increased pressure drop along the artery. As a consequence of the reduction in arterial blood pressure towards the periphery, the vascular diameter of the conduit vessel would decrease. However, several previous investigators (2-4), using plethysmographic methods, have found that increased blood flow was associated with an increase in the cross section of the femoral artery. Similar dilatation responses were obtained whether femoral blood flow was raised by stimulation of the sciatic nerve, injection of acetylcholine or injection of other

Section: Lie Sejersted Kiilmentioning

confidence: 99%

Local Regulation of Vascular Cross Section during Changes in Femoral Arterial Blood Flow in Dogs

Lie

Sejersted

Kiil

1970

140

“…Except during the preliminary experiments, blood pressure was maintained at a constant level by a pressure-stabilizing device (13) connected by a plastic tube to the right femoral artery. At the beginning of these experiments heparin (500 IU/kg) was injected as an anticoagulant, and a supplementary dose (150 IU/kg) was administered every hour.…”

Section: Introductionmentioning

confidence: 99%

Sympathetic Control of Canine Abdominal Aorta

Gerová

Gero

Dolezel

et al. 1973

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,

“…Changes in sympathetic activity induced by reflexes have been stated to cause an active change in diameter of the femoral artery (7,8), but in these experiments the possible role of blood-borne vasoactive substances could not be ruled out. Moreover, the concept of a direct nervous pathway for the sympathetic control of conduit vessels seems to be weakened by recent data pointing to a relatively sparse adrenergic innervation and especially to the relatively large distance between adrenergic nerve terminals and smooth muscle in the vessel wall (9)(10)(11), both of which might impair direct neuroeffector transmission.…”

mentioning

confidence: 96%

Range of the Sympathetic Control of the Dog Femoral Artery

Gerová

Gero

1969

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..