The action of vasoactive drugs on longitudinal and circular muscle of dog mesenteric vein

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Abstract
The dog anterior mesenteric vein has outer longitudinal and inner circular muscle layers. The response of the vein to drugs was recorded without disrupting the muscle arrangements by combining constant-flow perfusion of a segment with isometric recording of longitudinal tension. Noradrenaline and acetylcholine were potent stimulants. Tachyphylaxis developed to histamine, 5-hydroxytryptamine and angiotensin. Cocaine and guanethidine potentiated the responses to noradrenaline and fluorescent microscopy confirmed the presence of adrenergic nerves in both muscle layers. Isoprenaline partially relaxed the stimulated vein and this action was blocked by propranolol. Evidence was obtained which suggests the existence in the vein of specific receptors for several of the agonists investigated.