Effect of plasma from hypertensive patients on contractile response of vascular smooth muscle from normotensive rat

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Abstract
This study examines whether incubation with plasma from essential hypertensive patients increases the contractile activity of vascular smooth muscle from rats in response to noradrenaline (NA) and potassium (K+). Plasma samples were obtained from age- and sex-matched essential hypertensive patients and normotensive people. Vascular strips were prepared from aorta and portal veins of normotensive rats and placed in physiological solution in muscle baths for measurement of mechanical response. Aortic strips exposed to hypertensive plasma showed increased responsiveness to NA compared with normotensive plasma, but K+ caused an opposite effect. Portal vein exposed to normotensive or hypertensive plasma did not produce any response to NA, but the responsiveness produced in the presence of normotensive plasma to K+ was higher than that of hypertensive plasma. Portal vein exposed to normotensive plasma or hypertensive plasma showed a dose-dependent increase in the spontaneous activity up to 50% concentration of the plasma samples, but further increase in the concentration of plasma inhibited the spontaneous activity. Spontaneous activity at any given concentration of hypertensive plasma was significantly higher than that of normotensive plasma. The spontaneous activity in the presence of heated or unheated normotensive plasma or unheated normotensive serum was not significantly different from each other. These results indicate that the plasma factor from hypertensive patients, which alters the reactivity of vascular smooth muscle from normotensive rat, is present in the serum fraction and is not heat sensitive.Key words: hypertension, plasma, contractile response, circulating factor, spontaneous activity.

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