title: Myocardial infarct size-limiting effect of chronic hypoxia persists for five weeks of normoxic recovery.
abstract: We examined cardioprotective effect of chronic hypoxia and the time course of its recovery under normoxic conditions. Adult male Wistar rats were exposed to intermittent hypobaric hypoxia (7000 m, 8 h/day, 35 exposures) and susceptibility of their hearts to ischemia-induced ventricular arrhythmias and myocardial infarction was evaluated in anesthetized open-chest animals subjected to 30-min coronary artery occlusion and 4-h reperfusion on the day after the last hypoxic exposure and at 7, 35 and 90 days of normoxic recovery. The infarct size was reduced from 69.2+/-1.7 % of the area at risk in normoxic controls to 48.0+/-2.2 % in the chronically hypoxic group and to 61.6+/-2.3 % in the group recovered for 7 days. This residual protection persisted for at least 35 days of normoxic recovery but it was absent after 90 days. In contrast to the infarct size-limitation, the antiarrhythmic protection disappeared already during the first week; the incidence of ventricular fibrillation was even significantly increased 7 and 90 days after the last hypoxic exposure. In conclusion, the duration of cardioprotection induced by chronic hypoxia differs markedly, depending on the end point of ischemia/reperfusion injury examined. Whereas the increased tolerance to lethal myocardial injury persists for at least 5 weeks after the termination of hypoxia, the antiarrhythmic protection rapidly vanishes, being replaced with transient proarrhythmic effect.
authors.affiliation: Institute of Physiology, Academy of Sciences of the Czech Republic, Centre for Experimental Cardiovascular Research, Prague, Czech Republic.
authors.forename: J
authors.initials: J
authors.lastname: Neckár
authors.forename: B
authors.initials: B
authors.lastname: Ostádal
authors.forename: F
authors.initials: F
authors.lastname: Kolár
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002908:Chronic Disease; D000860:Hypoxia / Q000150:complications / Q000473:pathology* / Q000503:physiopathology*; D015994:Incidence; D008297:Male; D009203:Myocardial Infarction / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D020127:Recovery of Function / Q000502:physiology*; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D012720:Severity of Illness Index; D014693:Ventricular Fibrillation / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*