Studies on Human Platelet Glycolysis. Effect of Glucose, Cyanide, Insulin, Citrate, and Agglutination and Contraction on Platelet Glycolysis*

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Abstract
Evidence for a metabolically active plasma-free platelet system is presented. Glycogenolysis was found to be a potent pathway for lactate production. Aerobic glycolysis constituted a major fraction of glucose metabolized. Both insulin and cyanide increased lactate production in the presence of glucose. The Krebs cycle appeared to be operative for ATP synthesis when citrate was used as substrate. The first stages of gluconeogenesis were noted to be present. Glucose uptake contributed to increased lactate production. Thrombin, epinephrine, and ADP resulted in platelet agglutination and contraction and increased platelet glycogenolysis (phosphorylase activity). Epinephrine appeared to be a more potent activator of phosphorylase, resulting in a 70% increase in glucose 6-phosphate levels. Thrombin and epinephrine both increased glucose uptake and lactate production. Glucose uptake decreased in the presence of ADP. Except for incubations with epinephrine, glucose 6-phosphate remained constant under conditions in which lactate flux increased 3-fold and glucose uptake increased 2-fold. Thrombin, epinephrine, and ADP decreased ATP levels in the presence or absence of glucose.