Effect of human plasma proteins on spontaneous contractile activity of rat mesenteric portal vein

Abstract

This study examines the effect of various plasma proteins from man on the spontaneous contractile activity of the rat portal vein. Albumin, γ-globulin, α-globulin, β-globulin (the major plasma proteins), and immunoglobulin IgG (the major immunoglobulin present in the γ-globulin fraction) were obtained commercially. Mesenteric portal vein strips were prepared from rats and placed in a physiological salt solution in muscle baths for the measurement of longitudinal mechanical response. Portal veins exposed to albumin or γ-globulin showed a dose-dependent increase in the spontaneous activity, whereas those exposed to α-globulin or α - and β-globulin together showed a dose-dependent inhibition of spontaneous activity. Immunoglobulin IgG produced a dose-dependent increase in the spontaneous activity similar to that of γ-globulin. The increased spontaneous activity produced by albumin was not prevented by ouabain but was inhibited by phentolamine. Spontaneous contractile activity was stimulated by albumin in the chemically (6-hydroxydopamine) denervated portal vein. These findings indicate that albumin acts in a manner similar to noradrenaline. The increased spontaneous activity caused by γ-globulin (IgG) was inhibited by ouabain or verapamil. The effect of IgG was not dependent on α-adrenergic, cholinergic, histaminergic, serotoninergic, or renin angiotensin systems nor was it affected by removal of the endothelium. These observations may have implications in the pathophysiology of essential hypertension.Key words: vasomotion, mesenteric portal vein, plasma proteins, albumin, γ-globulin, inhibitory factor, stimulatory factor, IgG.