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Production of heat shock protein 70 (HSP70) in the heart is induced by hemodynamic stress, but its intracellular signal transduction system has not been elucidated well.To investigate the hypothesis that protein kinase A (PKA)-dependent and protein kinase C (PKC)-dependent systems are involved in the pressure-induced expression of HSP70 mRNA in perfused adult rat heart.Isolated tetrodotoxin-arrested Sprague–Dawley rat hearts were perfused as Langendorff preparations at a constant aortic pressure of 60 mmHg. Aortic pressure in rats of the pressure-overloaded group was elevated from 60 to 120 mmHg for 2–120 min. cAMP contents and rates of synthesis of protein were measured by radioimmunoassay and the incorporation of [14C]phenylalanine into total heart protein, respectively. Expression of HSP70 mRNA was determined by Northern blot analysis.Elevation of aortic pressure significantly increased cAMP content after 2 min of perfusion (by 41%), significantly increased rates of synthesis of protein during the second hour of perfusion (by 41%), and induced expression of HSP70 mRNA maximally after 60 min of perfusion (2.7-fold the control value). Exposure to glucagon, forskolin or 1-methyl-3-isobutylxanthine mimicked increases in these parameters caused by elevation of aortic pressure. Administration of a selective PKA inhibitor, H-89, significantly prevented induction of increases in expression of HSP70 mRNA and rates of synthesis of protein by a high pressure overload and exposure to agents that increase cAMP content. Furthermore, administration of phorbol ester induced expression of HSP70 mRNA. Administration of a PKC inhibitor, calphostin C, significantly prevented induction of increases in expression of HSP70 mRNA by a pressure overload and by exposure to phorbol ester.These results suggest that the pressure-induced induction of production of HSP70 is regulated both by PKA-dependent and by PKC-dependent systems during periods of active synthesis of protein in adult rat heart.