STEGALL, V.S.*; KINSEY, S.A.; MCLELLAN, W.A.; DILLAMAN, R.M.; PABST, D.A.: Biochemical changes in locomotor muscle of harbor porpoise, Phocoena phocoena, during starvation.
A primary locomotor muscle (m. longissimus) of stranded, emaciated porpoises was compared to that of robust porpoises killed in fishing operations. We previously demonstrated that emaciated porpoises displayed decreases in body mass, axial locomotor muscle mass, m. longissimus muscle fiber diameters and fast twitch fiber-type areas equivalent to, or greater than, that seen in laboratory animals undergoing starvation. This study investigates changes in muscle biochemical profiles of starved (n=5) and robust (n=4) porpoises. A suite of enzymes were assayed representing glycolysis, lipid oxidation, citric acid cycle, and amino acid oxidation. We report here the activities (MUmoles/min.*g wet wt.) for citrate synthase (CS), lactate dehydrogenase (LDH) and hexokinase (HK). CS was chosen as a representative enzyme for the citric acid cycle; we hypothesized its relative activity would increase during starvation because of the increased need for lipid oxidation. LDH was chosen to monitor the muscle’s anaerobic metabolism; we hypothesized its relative activity would decrease because of the increased atrophy of fast twitch fibers. HK was chosen as a representative enzyme for glycolysis; we hypothesized its relative activity would decrease because of the loss of glycogen during starvation. Our results showed that CS increased by 49%, LDH decreased by 40%, HK decreased by 35% and the ratio CS/LDH increased by 37% in starved animals. These results support the histochemical study and suggest a transition to the use of oxidative slow twitch fibers as the reliance of metabolic fuel changes from glucose to lipid during starvation. Research supported by Marine Mammal Health and Stranding Response Program, NMFS, ONR, UNCW-CMS, and Sigma-Xi GIAR.