Control of Glucose Balance in the Perfused Rat Liver by the Parasympathetic Innervation

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Abstract
Electrical stimulation of the nerve bundles around the hepatic artery and the portal vein activates both the sympathetic and parasympathetic liver nerves; the sympathetic effects clearly predominate. Parasympathetic effects were therefore studied in the rat liver perfused in situ by perivascular nerve stimulation in the presence of both an .alpha.- and a .beta.-blocker. (1) In the presence of the .alpha.-blocker phentolamine and the .beta.-blocker propranolol all sympathetic nerve effects were prevented; the remaining parasympathetic stimulation had no influence on the basal glucose and lactate metabolism nor on the hemodynamics. (2) Insulin alone, with both .alpha.- and .beta.-blockade, provoked a small, parasympathetic nerve stimulation in the presence of insulin a more pronounced enhancement of glucose utilization. (3) In the presence of an .alpha.- and .beta.-blocker perivascular nerve stimulation antagonized the glucagon stimulated glucose release, but did not affect lactate exchange. The nerve effect was abolished by the parasympathetic antagonist atropine. (4) Acetylcholine or insulin, with both an .alpha.- and .beta.-blocker present, mimicked the effects of nerve stimulation antagonizing the glucagon-stimulated glucose release. Nerve stimulation in the presence of insulin was more effective than either stimulus alone. The present results show that in rat liver stimulation of the parasympathetic hepatic nerves has direct effects on glucose metabolism synergistic with insulin and antagonistic to glucagon.

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