Heat And Run, Genomic And Morphological Aspects Of Adaptation In The Rat‘s Heart: 2424: Board #69 May 29 8:00 AM - 9:30 AM

INTRODUCTION: Heat acclimation (AC) and exercise training (EX) individually improves mechanical and metabolic performance of the isolated rat's heart. Combined heat acclimation and exercise training (EXAC) demonstrates an interactive/additive effect, manifested by greater systolic pressure generation than that shown by either alone. Given the opposing adaptive requirements of the two stressors, the underlying mechanisms of the combined EXAC affect is as yet unknown.
PURPOSE: 1. in vivo assessment of the physiological adaptation to the stressors 2.determing global genomic responses using gene profiling analyses 3. linking physiological and genomic responses.
METHODS: Rats were divided into: AC, EXAC (30d, 34°C), C, EX (30d, 24°C) groups. For Exercise training a progressive treadmill protocol was applied; In vivo cardiac performance was monitored using Echocardiology; global genomic response of homeostasis associated genes was detected using cDNA microarray.
RESULTS: Increased thickness of posterior and septum walls coincidentally with decreased chamber diameter was demonstrated in EX and EXAC groups. Longer duration of left ventricular ejection and circumferential fiber shortening, implying decreased contractile velocity was evident in the heat treated groups. Gene profiling demonstrated transcript upregulation in a stress specific manner. Focusing on metabolic, transport, stress and signaling GO categories, we demonstrated that EX and EXAC upregulated 37 and 43% (in metabolic) while AC and EXAC upregulated 25 and 21% (in transport) genes. Other categories changed similarly in all groups.
CONCLUSION: Exercise training was manifested in morphological changes; chronic heat overrided exercise training mediated contractile response. Principally, both stressors upregulated gene expression. Different gene profiles were detected, however, following the various treatments. Training affected metabolic pathways (most pronouncedly in the EXAC) while exposure to heat induced changes in genes linked to transport, EC coupling mechanism and cytoprotection. Concerted gene upregulation in all functional categories, in EXAC only, may account for the advantage in pressure generation seen in this group.