Tolerance to hypoxia of myocardium from adult and aged spontaneously hypertensive rats.
Myocardial mechanics and high-energy phosphate content [ATP and creatine phosphate (CrP)] of isolated left ventricular papillary muscle preparations from male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) were compared at 6 and 18 mo of age. In comparison with oxygenated (95% O2-5% CO2) glucose-supplied (5.5 mM) papillary muscles from hearts of WKY rats, papillary muscles from hypertrophied hearts of the 18-mo-old SHR exhibited a prolonged time to peak tension, electromechanical delay time, and an increase in resting tension measured at the apex of the length-tension curve. Adenine nucleotide (ATP and ADP) contents of oxygenated papillary muscles were not significantly different between SHR and WKY strains at 6 or 18 mo of age, but CrP content of hearts from adult WKY and SHR were higher than for aged WKY and SHR rats. For up to 30 min of hypoxia (95% N2-5% CO2), muscles from the 18-mo-old SHR and WKY rats demonstrated improved tolerance to hypoxia compared with muscles from younger animals. However, at 60 min of hypoxia the 18-mo-old SHR demonstrated lower active tension and adenylate energy charge [(1/2 ADP + ATP)/(ATP + ADP + AMP)]. At higher glucose concentrations (22 mM), both 18-mo-old WKY and SHR demonstrated improved tolerance to hypoxia; moreover, the differences between strains were no longer evident. Following reoxygenation with 5.5 mM glucose, contracture tension and CrP content recovered to near prehypoxic control levels, whereas developed tension and ATP content remained moderately depressed for all groups.(ABSTRACT TRUNCATED AT 250 WORDS)