EFFECT OF UNDERNUTRITION ON CONTRACTILE AND FATIGUE PROPERTIES OF RATDIAPHRAGM DURING DEVELOPMENT

The present study was designed to assess the effects of combined pre- and postnatal undernutrition on the in vitro contractile and fatigue p roperties of the rat diaphragm during development. In vitro direct sti mulation of Costal diaphragm from control (CTL) and undernourished (UN ) rats was done on postnatal days 1, 4, 14, 21, 30, 40, 50, and 60. Co mbined pre- and postnatal undernutrition resulted in stunted animal gr owth but did not alter the diaphragm-to-total body weight ratio. Twitc h contraction time, half-relaxation time, and force-frequency relation ships were not consistently affected by undernutrition. Specific twitc h force and specific tetanic force were also unchanged in the UN group . Fatigue resistance was high and comparable in UN and CTL groups at d ays 1 and 4. At day 14 and thereafter, fatigue resistance declined but was consistently higher in the UN than in the CTL group. We conclude that combined pre- and postnatal undernutrition results in a significa nt increase in fatigue resistance of the diaphragm compared with CTL, whereas diaphragm muscle contractile properties are not appreciably af fected by prolonged undernutrition.