The role of intramural noradrenaline in the potassium induced contracture of non-estrogenized smooth muscle.

The influence of intramural noradrenaline on potassium induced contractures was studied in isolated preparations of the uterus and the portal vein of the rat. Uterine strips of oophorectomized rats responded with contraction followed by transient relaxation when immersed in a medium containing 127 mM potassium chloride. Reserpinization or blockade of beta-adrenoceptors with propranolol greatly diminished the transient relaxation. In the isolated portal vein, both noradrenaline depletion with reserpine and alpha-adrenoceptor blockade (phentolamine) reduced the active tension produced in response to the isotonic potassium solution. These results suggest that intramural noradrenaline plays a significant role in the development of contractures evoked by potassium in the uterus and the portal vein of the rat. In the uterus, the released noradrenaline counteracts the development of active tension, whereas in the portal vein, noradrenaline has a contractile effect which is added to that of potassium. Estrogen treatment reduced (portal vein) or abolished (rat uterus) the contractile effects of intramural noradrenaline. The adrenolytic effect of estrogen is possibly due to reduction in the release of noradrenaline from the sympathetic nerve-endings.