CONTRACTILE RESPONSES OF SPIRAL STRIPS OF LARGE BLOOD VESSELS FROM RABBITS TO TRANSMURAL STIMULATION AND TYRAMINE

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Transmural electrical stimulation with repetitive pulses of short duration causes contraction 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 (gutrelaxing) 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.
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