Contractile Responses of Spiral Strips of Large Blood Vessels From Rabbits to Transmural Stimulation and Tyramine

Abstract

Transmural electrical stimulation with repetitive pulses of short duration causes contrac tion of isolated vascular smooth muscles, which is suggested to correlate with excitation of adrenergic nerve terminals innervating the vascular wall (1,2). This is supported by findings which indicated that field stimulation causes contraction and an increased efflux of <SUP>3</SUP>H-noradrenaline from rabbit main pulmonary arteries (3) and that a biologically active (gut relaxing) substance is released from stimulated rabbit ear arteries (4). Tyramine releases noradrenaline from the stored site that is not accessible to nerve impulses (5). Excitatory responses of the vascular smooth muscle to electrical and chemical stimulation are thought to relate directly to functional noradrenaline involved in the different pools of nerve terminals.<BR>The aim of the present study was to examine contractile responses of ascending and thoracic aortae and the main pulmonary and superior mesenteric arteries to transmural stimulation, tyramine and dopamine, in comparison with noradrenaline. Since arterial strips have a capacity to accumulate and retain noradrenaline when applied exogenously at high concentrations (6,7), the contractile response to the electrical and chemical stimulation was also investigated in arterial strips after exposure to noradrenaline or dopamine. METHODSAlbino rabbits of both sexes weighing 1.8 to 2.2kg were sacrificed by bleeding from com mon carotid arteries. The main pulmonary artery, ascending aorta and a part of the thoracic aorta (middle part between the aortic arch and the diaphragm) and the superior mesenteric artery were isolated and adherent tissues removed. These vessels were spirally cut into strips of approx. 5 .25 mm in size (for the former three vessels) and 3 ,,, 25 mm (for the mesenteric artery). Specimens were suspended in a muscle bath of 100 ml capacity con taining the nutrient solution and adjusted to a resting tension of 2 g. Isometric contractions of the vascular smooth mucle were recorded on a two-channel penwriter (Sanei Sokki Co.) by means of a force-displacement transducer (Nihonkoden Kogyo Co.). Temperature of the bath was maintained at 37/ _=0.5 C and the solution bathing the vascular strips was continuously aerated with a mixture of 95 % oxygen and 5 , carbon dioxide. Before measurements were begun, preparations were allowed to equilibrate for longer than 2 hr in the nutrient solution of the following composition (mM): Na+, 162.1; K+, 5.4; Ca++

Potentiation of the Contractile Response of Isolated Aortae to Transmural Stimulation by Angiotensin

“…It has been suggested that contractions induced by transmural stimulation under conditions used in the present study result from nor adrenaline released by excitation of adrenergic nerves (9). Similar potentiation of re sponses to sympathetic nerve stimulation by angiotensin has been observed in isolated rabbit hearts (11), isolated rabbit portal veins and coeliac arteries (3), cat mesenteric blood vessels (5) and dog saphenous veins (12).…”

Modification by Temperature of the Response of Isolated Aorta to Stimulatory Agents and Transmural Stimulation

“…The method for stimulating intramural adrenergic nerves was the same as that described in an earlier report [13]. Square pulses of a 0.3-msec duration with supramaximum intensity (approximately 80 V [15]) at frequencies of 5 and 20/sec for 40 and 10 sec, respectively (thus total pulses applied being 200), were transmurally applied. Electrical pulses were provided by an electronic stimulator (type WSE-3R, Nihonkoden Kogyo).…”

Contractile Responses of Isolated Rabbit Aortae to Transmural Stimulation as Affected by Calcium, Strontium, Sodium and Ouabain

“…The vascular strips were placed between a pair of stimulating electrodes (platinum plates, 5 x 15 mm), as described by Toda, Usui and Mori (23). The prepartions were transmurally stimulated by a train of 0.3 msec-rectangular pulses of supramaximal intensity (about 80 V) applied at frequencies of 5, 20 and 100/sec.…”

“…The number of the electrical pulses was kept constant (200 pulses) by changing the period of stimulation (40, 10 and 2 sec for frequencies of 5, 20 and 100/sec, respectively). Contractile response to electrical stimulation applied under these conditions is shown to result from released noradrenaline (23). Electrical stimuli were provided by an electronic stimulator (Type WSE-3R, Nihon koden Kogyo Co.).…”