Autonomic vasomotor responses in the canine hepatic arterial and venous beds

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Abstract
Blood flows (electromagnetic flowmeter) and pressures were recorded simultaneously in the hepatic artery and portal vein during left splanchnic nerve stimulation, and during injections of adrenergic substances and of methacholine into the hepatic artery and into the portal vein, before and during progressively increasing adrenergic blockade induced by Ilidar or Dibenzyline injected into the hepatic artery and into the portal vein. During the cannulation procedure it was observed that temporary occlusion of the portal vein caused a much greater fall of arterial pressure than did occlusion of the splenic vein. Intra-arterial and intravenous injections of arterenol, and splanchnic nerve stimulation all had qualitatively similar effects. All caused constriction as indicated by an increase in resistance to flow in both the hepatic arterial and portal venous vascular beds. Epinephrine was slightly more potent than either of the other stimuli and the hepatic artery bed was slightly more responsive to the adrenergic substances than was the portal venous bed. Adrenergic blockade progressively abolished the constrictor responses in both beds to epinephrine, arterenol and sympathetic nerve stimulation without inducing significant reversal. No sympathetic, adrenergic (isoproterenol), or cholinergic dilator responses were observed in either hepatic bed. These results are in contrast to those of the mesenteric artery bed which gave dilator responses to isoproterenol, and to epinephrine during partial adrenergic blockade. Both hepatic beds gave less marked vasoconstrictor responses to the adrenergic substances and to splanchnic stimulation than did the previously reported mesenteric artery bed.