NORMOBARIC HYPOXIA ALTERS METABOLIC PROPERTY IN RAT DIAPHRAGM

Abstract

It is well established that exposures to hypoxia results in physiological adaptation in both human and animals. Recently, from the viewpoint of erythropoiesis, normobaric hypoxic environment has been applied for conditioning and exercise training in flats. However, no studies have examined the adaptation of respiratory muscle under normobaric hypoxic environment. PURPOSE: To examine effects of normobaric hypoxia on metabolic properties of diaphragm, we measured glycolytic and oxidative enzyme activities of rat diaphragm after 50 days exposure to normobaric hypoxia. Furthermore, we studied their changes after the exposure to hypoxia. METHODS: Seventy male Wistar rats (8 weeks old) were randomly assigned to a normobaric hypoxia (H) group or an aged-matched normoxia (N) group. H group was housed in a normobaric hypoxic room (15.4%O2) for 50days and then it was moved into a normoxic room for 50 days. At the 0, 25th, 50th, 75th, 100th day of the experiment period, 7- 8 rats of each group were anesthetized with pentobarbital sodium. Costal diaphragm was removed, frozen in liquid nitrogen and stored at -80oC until assay. Lactate dehydrogenase (LDH) and citrate synthase (CS) activities were determined spectrophotometrically immediately following homogenization.ü@ RESULTS: LDH activity was increased with aging, on the other hand CS activity was decreased. H group showed significantly (p < 0.05) higher LDH activity (H: 986 ± 56 vs N: 907 ± 44 μmol/mg/min) at the end of the hypoxia period. However the increase was back to the same level of N group at 25 days after the hypoxia period. CS activity did not differ between both groups. As a result, LDH/CS ratio was similar to the change of LDH activity. CONCLUSION: These data indicate that exposure to normobaric hypoxia can enhance glycolytic capacity in diaphragm and that the effect would not be maintained under normoxic condition for so long.