Metabolite accumulation increases adenine nucleotide degradation and decreases glycogenolysis in ischaemic rat skeletal muscle D.G. WELSH and M.I. LINDINGER Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada ABSTRACT Adenine nucleotides and glycogen are degraded in skeletal muscle during no-flow ischaemia. Past investigations have ascribed these metabolic changes to the severe energetic stress which arises with the removal of exogenous substrates (principally oxygen). We tested this hypothesis by measuring the high-energy phosphagen and glycogen contents of stimulated rat hindlimb muscles (1 twitch s )1 ) prior to and following 40 min of no-¯ow ischaemia or hypoxic perfusion without glucose (P a o 2  4:6  0:1 torr, plasma glucose  0:3  0:1 mmol L )1 ). Both experimental protocols eliminated exogenous substrate supply; however, the maintenance of ¯ow during hypoxic perfusion ensured the removal of metabolic by-products. A period of forty minutes of skeletal muscle ischaemia was characterized by reductions in the total adenine nucleotide pool, phosphocreatine and glycogen in the slow oxidative soleus, fast oxidative-glycolytic plantaris and the fast glycolytic white gastrocnemius. Compared to ischaemia, the total adenine nucleotide pool was higher (by 7.2± 13.3 lmol g )1 dry wt) and the glycogen content lower (by 10.0±16.6 lmol g )1 dry wt) in skeletal muscle exposed to hypoxic perfusion without glucose. The ability of hypoxic perfusion to attenuate TAN degradation and augment glycogenolysis can be attributed to metabolic by-product removal. By limiting muscle lactate and PCO 2 accumulation, hypoxic perfusion without glucose attenuates cellular acidi®cation; this could in turn limit AMP deaminase activation and glycogen phosphorylase inhibition. We conclude that the ischaemia-induced alterations in adenine nucleotide and glycogen metabolism arise in response to the elimination of exogenous substrates and to the accumulation of metabolic by- products. Keywords adenine nucleotide degradation, glycogenolysis, hypoxia, intramuscular pH, ischaemia, lactate. Received 3 September 1996, Accepted 11 April 1997 In skeletal muscle, prolonged no-¯ow ischaemia de- pletes tissue of endogenous energy stores (Larsson & Hultman 1979, Harris et al. 1986, Idstrom et al. 1990, Welsh & Lindinger 1993). Traditionally, it has been presumed that adenine nucleotide, phosphocreatine and glycogen degradation arises solely in response to the elimination of exogenous substrates (principally O 2 ); this limits the availability of ATP for cellular homeo- stasis, thereby initiating a severe energetic stress (Lars- son & Hultman 1979, Idstrom et al. 1990, Sahlin et al. 1990). Implicit in this reasoning is the assumption that metabolic by-product accumulation (i.e. lactate, CO 2 ) has little or no effect on cellular metabolism during no- ¯ow ischaemia. The acceptance of this view has occurred despite an absence of strong experimental evidence; to date, most work has simply examined the magnitude and time course of these metabolic changes (Harris et al. 1986, Idstrom et al. 1990). Moreover, the current view overlooks in vivo and in vitro investigations showing that tissue acidi®cation in¯uences the activity of rate-limiting enzymes in both the glycogenolytic (glycogen phosphorylase) and the adenine nucleotide (AMP deaminase) pathways (Kasvinsky & Meyer 1977, Wheeler & Lowenstein 1979, Raggi & Ranieri-Raggi 1987). This study tested whether adenine nucleotide and glycogen degradation during no-¯ow ischaemia were singularly dependent on the elimination of exogenous Correspondence: Dr Michael I. Lindinger, Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada, N1G 2W1. Acta Physiol Scand 1997, 161, 203±210 Ó 1997 Scandinavian Physiological Society 203