METABOLIC-FATE OF GLUCOSE IN VASCULAR SMOOTH-MUSCLE DURING CONTRACTION INDUCED BY NOREPINEPHRINE

The metabolism of glucose in porcine carotid artery was tracked by iso topic methods during sustained isometric contraction induced by 100 mu M norepinephrine (NE). In resting muscles, 74 and 18% of glucose take n up was accounted for by glycolysis and glycogen synthesis, respectiv ely. Lactate production accounted for 69%, pyruvate production for 12% , and glucose oxidation accounted for 14% of glycolytic nux. The oxida tion of glucose accounted for 57% of the consumption of O-2 and thus c onstituted the primary oxidative substrate. During contraction by NE, glucose-uptake declined modestly below the resting basal rate. Glycoly sis of external glucose and Lactate production decreased and then incr eased with sustained contraction. Norepinephrine stimulated simultaneo us glycogenolysis and glycogen synthesis, with net glycogen synthesis prevailing over 90 min of isometric contraction. Furthermore, NE modif ied the distribution of glucosyl units throughout the glycogen pool. T he steady state rate of oxidation of glucose did not increase during N E contraction, even though O-2-consumption increased. In contrast, inc reased glucose oxidation was demonstrable during contraction induced b y 80 mM KCl. Furthermore, oxidation of exogenous fatty acid could be d emonstrated during NE-induced contraction. Thus, NE exerts multiple ef fects on glucose and glycogen metabolism in smooth muscle, but it does not stimulate glucose oxidation. (C) 1998 Academic Press Limited.