Experimental approaches in muscle metabolism: hindlimb perfusion and isolated muscle incubations.

The perfusion of rat hindlimb muscles and the isolated in vitro muscle preparation are usually the preferred methods for investigating muscle metabolism. In light of recent concerns about the incubated muscle preparation, we have examined the problems, the advantages, and the viability of these two experimental techniques, with focus on glucose metabolism. A major advantage of the hindlimb perfusion system is that it maintains its metabolic viability very well, and perfusions in resting muscles can be achieved successfully with cell-free media. However, variations in the perfused rat hindlimb procedures result in considerable differences in perfusate flow among muscles, making quantitative comparisons among perfusion procedures difficult. Metabolic viability has been identified as a problem in some isolated in vitro muscle preparations. We have provided criteria to avoid muscle hypoxia. Minimum levels of insulin seem to be a key requirement to maintaining the muscle's viability, and essential amino acids are required to retard an increase in the basal rate of glucose and amino acid uptake. Under such conditions metabolic viability can be maintained during prolonged incubations (9-30 h). Both the isolated in vitro muscle preparation and the hindlimb perfusion preparation are viable models for the study of muscle metabolism.