Metabolic characteristics of experimental free vascularized canine gracilis muscle transfers

A canine gracilis model was used to study muscle energy metabolism and enzyme activities after free vascularized muscle transfer. Fifteen male mongrel dogs underwent orthotopic, free transfer of the left gracilis with microneurovascular anastomosis. After a minimum of 10 months' recovery, muscle biopsy specimens were obtained from the transfers and the contralateral controls and analyzed for relative fiber type areas and maximum activities of phosphorylase, hexokinase, phosphofructokinase, glycerol-3-phosphate dehydrogenase (GPDH), pyruvate kinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, 3-hydroxyacyl coenzyme A dehydrogenase (HAD), and creatine phosphokinase. Biopsy specimens obtained before and after a 10 minute, 20-Hz contraction were analyzed for glucose, glycogen, glycolytic intermediates, phosphocreatine, total creatine, and adenine nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, inosine monophosphate, and inosine). There was no significant transfer versus control difference in type I relative fiber area (45 +/- 4 percent versus 44 +/- 3 percent). Total creatine was significantly reduced in the transferred muscles relative to control (83.1 +/- 3.0 mmol/kg versus 100.6 +/- 5.1 mmol/kg dry weight). Maximal activities of phosphorylase, pyruvate kinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, HAD, and creatine phosphokinase were diminished in transfers relative to controls, although hexokinase activity was significantly higher in the freely transferred gracilis muscles. During the 20-Hz contraction, muscle transfers produced less force initially, although the force/time integral over the 10-minute stimulation was similar in transfers (277 +/- 25 N/g/second) and controls (272 +/- 24 N/g/second). The contraction was associated with significant glvcogen use and lactate accumulation in both transfers and controls, although this was less pronounced for the transfers. Glycolytic flux appeared muted in the transfers relative to controls. Significant, similar high-energy phosphagen reductions and inosine monophosphate accumulation were noted during the contraction in both groups. Contractile activity is associated with the expected pattern of muscle metabolite changes following free vascularized transfer, indicating the components of cellular energy metabolism are not qualitatively altered after microneurovascular muscle transfer. In contrast, quantitative differences suggest that free vascularized muscle transfer can be associated with a muscle enzyme profile consistent with deconditioning and the presence of denervated muscles fibers in the absence of fiber type profile changes.