Metabolism of coronary arteries and arterioles: A histochemical study

Abstract

Because of sample size limitations, very little if any information is available concerning the biochemistry and metabolism of coronary arterioles. Using the histochemical approach, we studied glycolysis, β-oxidation of fatty acids, the Krebs cycle, and the respiratory chain in coronary arteriolar smooth muscle. In addition, the activities of myosin ATPase and other energy-consuming reactions were also determined. Our results suggest that the metabolism of coronary arterioles is predominately aerobic in nature with the strong possibility that fatty acids serve as the major energy source. The aerobic nature of microvascular metabolism is suggested by: (a) a low glycolytic potential as reflected in weak reactions for glycogen, α-glycerophosphate dehydrogenase, and lactate dehydrogenase; (b) high Krebs cycle activity as indicated by intensity of isocitrate, succinate, and malate dehydrogenase reactions; (c) high respiratory chain activity as reflected by heavy deposition of reaction products of ubiquinone and cytochrome oxidase; (d) preference for lipid as metabolic substrate as revealed by strong reactions for free fatty acids and β-hydroxybutyrate dehydrogenase. Myosin ATPase activity was greater in coronary arterioles than in the larger arteries, suggesting a more active contractile apparatus in the microvessels. When compared to the arterioles, the histochemical profile of small and intermediate coronary arteries revealed high potential for anaerobic glycolysis and very low oxidative activities. In view of this metabolic heterogeneity within the coronary vasculature, we suggest that data obtained from small coronary arteries cannot be extrapolated to the coronary microvasculature.