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

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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.