Age dependence of heat stress mediated cardioprotection

Background. To study the influence of age on heat stress cardioprotection, functional recovery, nucleotide concentrations, and heat stress protein 70 (Hsp70) levels were compared in the heat stressed (HS) and control (C) hearts at different ages, in a protocol mimicking donor heart preservation for transplantation. Methods. Control and heat stressed (24 hours before experiment) rat hearts were divided into three age groups: (I) 1 month, (Y) 4 months, and (M) 16 months (n = 6). Left ventricle balloon catheter was used to determine systolic and end-diastolic pressure/volume relations before and after 4 hours of cardioplegic arrest at 4°C. Another identical set of isolated hearts underwent 5 minutes of normoxic perfusion to obtain preischemic Hsp70 content and metabolite concentrations. Results. The postischemic recovery was highest in group HS-Y as compared to C-Y, HS-I, C-I, HS-M, and C-M. There were no differences in preischemic adenine nucleotides or creatine metabolite concentrations between the three age groups. In contrast, the nicotinamide adenine dinucleotide (oxidized form) (NAD+) and nicotinamide adenine dinucleotide phosphate (oxidized form) (NADP+) concentrations were significantly raised in group HS-Y. Hsp70 content was increased in all HS groups with no difference between the age groups. Conclusions. Improved postischemic functional recovery after cardioplegic arrest was observed in the young adult HS hearts. This was associated with highest NAD+ and NADP+ concentrations and did not correlate with increased Hsp70 content.