The Contractility of the Diaphragm under Hypoxic Conditions in Aged Rats

Abstract

Background: Hypoxia is a common feature in several respiratory diseases. It is known to impair force generation and increases fatigability of respiratory and peripheral skeletal muscles. The precise mechanisms involved in hypoxia-induced impairment in contractile performance are incompletely understood, but oxidative and nitrosative stress could be at play. Little is known about the effects of hypoxia on the contractility of aged muscles. Aim: To investigate the effect of aging on the contractility of unfatigued diaphragm under hypoxic conditions. And to ask whether there is an age-specific difference in oxidative damage that could partially account for the differential response of the contractility of the diaphragm to hypoxia with age. Materials and Methods: This experimental work was conducted on 2 groups of albino rats. Group I was the young adult rats (aged 8mo n=10). Group II was the old one (aged 24mo,n=10). Rat diaphragm muscle strips from each group were studied in vitro while aerated with 95% O 2-5% CO 2 (hyperoxia ,n=10) or 95% N 2-5% CO 2 (hypoxia,n=10). Results: The contractility was significantly decreased in old rats when compared with young rats specially under hypoxic conditions. On the other hand the markers of oxidative stress; MDA and nitrotyrosine were significantly higher in old rats than adults. Conclusion: There is an age-specific difference in oxidative damage that could partially account for the differential response of the contractility of the unfatigued diaphragm to hypoxia with age.