Significance of glucose for mechanical activity, flavin and pyridine nucleotide oxidation-reduction changes in isolated rat portal veins under ACh-stimulation

The influence of extracellular glucose on isometric concentrations induced by acetylcholine was investigated under aerobic conditions in rat portal veins. In order to estimate the contractile potency of acetylcholine (ACh), dose-response curves of ACh and nor-epinephrine (NE) were compared. Simultaneously with the mechanical activity, changes in the redox states of pyridine nucleotides (PN) and flavoproteins were detected by a surface-fluorimetric method. Tissue concentrations of glucose, lactate, pyruvate, and ATP were determined parallel to ACh-induced contractions at corresponding intervals. In response to ACh-induced contractions, PN and flavoproteins were oxidized in vessels supplied with glucose. Following 6 h of glucose withdrawal, a small reduction or no change in the redox state was observed; ACh-induced contractions and tissue concentrations of glucose, lactate, pyruvate, and ATP were decreased. When glucose was added, the contraction force was restituted, and the tissue concentrations of glucose, lactate and PN were increased again. The ATP concentration remained decreased. The results suggest that isometric contractions of portal veins are significantly influenced by aerobic glycolysis. A direct effect of glucose on the excitability of vascular smooth muscle is discussed.