Inhibitory Effects of Glucose Utilization by Gymnema Acids in the Guinea-Pig Ileal Longitudinal Muscle.
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概要
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Two substances identified as ((3β, 4α, 16β, 21β, 22α)-21-tigloxy-16, 22, 23, 28-tetrahydroxyolean-12-en-3-yl-β-D-glucopyranosiduronic acid) (GA<SUB>1</SUB>) and ((3β, 4α, 16β, 21β, 22α)-21-(2-methylbutyroxy)-16, 22, 23, 28-tetrahydroxyolean-12-en-3-yl-β-D-glucopyranosiduronic acid) (GA<SUB>2</SUB>) identified among the gymnemic acids are triterpene glycosides extracted from Gymnema sylvestre leaves. We examined the effects of GA1 or GA2 on high K<SUP>+</SUP>-induced contraction in the guinea-pig longitudinal muscle. A sustained muscle contraction induced by hyperosmotically added 65.4mM KCl (H-65K<SUP>+</SUP>) was suppressed by GA<SUB>1</SUB> or GA<SUB>2</SUB> (7.7×10<SUP>-5</SUP>M). Simultaneous measurements of reduced pyridine nucleotide (PNred) or oxidized flavin protein (FPox) by the fluorescence technique and of contractile force revealed that GA<SUB>1</SUB> and GA<SUB>2</SUB> reduced the increase of PNred fluorescence and contractile force induced by H-65K<SUP>+</SUP>, whereas FPox fluorescence induced by it further increased. Reduced muscle contraction induced by GA<SUB>1</SUB> or GA<SUB>2</SUB> was restored by 5.5mM pyruvate. Simultaneous measurements of intracellular Ca<SUP>2+</SUP> [Ca<SUP>2+</SUP>] i level and contractile force indicated that [Ca<SUP>2+</SUP>] i level, which increased by H-65K+, hardly changed with GA<SUB>1</SUB> and GA<SUB>2</SUB>. In summary, both GA<SUB>1</SUB> and GA<SUB>2</SUB>, which are among the gymnemic acids, suppressed high K<SUP>+</SUP>-induced contraction in the guinea-pig ileal longitudinal muscle. The difference between these two gymnemic acids was not significant. The inhibitory effect of GA<SUB>1</SUB> and GA<SUB>2</SUB> on smooth muscle were assumed to be a result of inhibiting glucose uptake, which is an energy source of the muscle, whereas the inhibitory mechanisms were probably not mediated by Ca<SUP>2+</SUP>.
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