title: Heat acclimation-induced elevated glycogen, glycolysis, and low thyroxine improve heart ischemic tolerance.
abstract: Based on our observations of energy sparing in heat-acclimated (AC) rat hearts, we investigated whether changes in preischemic glycogen level, glycolytic rate, and plasma thyroxine level mediate cardioprotection induced in these hearts during ischemia-reperfusion insults. Control (C) (24 degrees C), AC (34 degrees C, 30 days), acclimated-euthyroid (34 degrees C + 3 ng/ml l-thyroxine), and control hypothyroid (24 degrees C + 0.02% 6-n-propyl-2-thiouracil) groups were studied. Preischemic glycogen was higher in AC than in C hearts [39.0 +/- 8.5 vs. 19.2 +/- 4.2 (SE) micromol glucose/g wet wt; P < 0.0006], and the lactate produced vs. glycogen level during total ischemia ((13)C-NMR spectroscopy) was markedly slower (AC: -0.82x, r = 0.98 vs. C: -4.7x, r = 0.9). Time to onset of ischemic contracture was lengthened, and the fraction of hearts experiencing ischemic contracture was lowered. Pulse pressure recovery was improved in AC compared with C animals before, but not after, absolute sodium iodoacetate-induced glycolysis inhibition. Acclimated-euthyroid hearts exhibited decreased ischemic tolerance, whereas induced hypothyroidism in C improved cardiotolerance. Thus higher preischemic glycogen and slowed glycolysis are associated with hypothyroidism and are likely important mediators of the improved ischemic tolerance exhibited by AC hearts.
authors.affiliation: Division of Physiology, Hadassah Schools of Dental Medicine and Medicine, The Hebrew University, Jerusalem 91120, Israel.
authors.forename: Mirit
authors.initials: M
authors.lastname: Eynan
authors.forename: Tanya
authors.initials: T
authors.lastname: Knubuvetz
authors.forename: Uri
authors.initials: U
authors.lastname: Meiri
authors.forename: Gil
authors.initials: G
authors.lastname: Navon
authors.forename: Gary
authors.initials: G
authors.lastname: Gerstenblith
authors.forename: Zohar
authors.initials: Z
authors.lastname: Bromberg
authors.forename: Yonathan
authors.initials: Y
authors.lastname: Hasin
authors.forename: Michal
authors.initials: M
authors.lastname: Horowitz
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D002247:Carbon Isotopes; D005947:Glucose / Q000493:pharmacokinetics; D006003:Glycogen / Q000378:metabolism*; D006019:Glycolysis / Q000502:physiology*; D006358:Hot Temperature; D007037:Hypothyroidism / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D017202:Myocardial Ischemia / Q000378:metabolism*; D015428:Myocardial Reperfusion Injury / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D010807:Physical Endurance / Q000502:physiology; D051381:Rats; D013974:Thyroxine / Q000097:blood*
chemical_list: D002247:Carbon Isotopes; D019344:Lactic Acid; D006003:Glycogen; D005947:Glucose; D013974:Thyroxine