[Role of nitric oxide in the development of the myocardial contractile reactions in trained animals].

Intensive constitutive production of nitric oxide (NO) during physical training improves vasodilatation and heart function. However, it remains unclear how NO takes part in myocardial adaptation to workload, which is accompanied by an increased heart inflow and intracellular calcium content. Using isolated rat heart by Langendorf preparation, we studied myocardial response to gradually increased left ventricular volume (Frank-Starling low) and increasing concentration of Ca2+ in the perfusion solution (from 1.7 mM to 12.5 mM) in trained and untrained rats. It was shown that 4 weeks swimming course improved heart function: heart rate was decreased; contractile activity (dP/dt max) and coronary flow were increased by 20% and 33%, respectively. Equal volume stretching of balloon in left ventricle provoked greater contraction in trained comparing to untrained hearts, demonstrating extended functional reserves after swimming course. Mitochondrial membrane potential was significantly increased in hearts of trained rats. Furthermore, training prevented fast increase of the end diastolic pressure during calcium upload. Mitochondrial factor release due to opening of mitochondrial permeability transition pore (MPTP) in trained hearts was detected at higher concentrations of calcium that reveals extended calcium capacity of mitochondria and lesser sensitivity of MPTP to its inductor-calcium. Blockade of NO synthesis with L-NAME application of (10(-4) M for 15 min) abolished reaction of trained heart during Frank-Starling and calcium upload. Thus, heart adaptation to physical training and extension of functional reserves in heart are provided by endogenous NO production. Key words: nitric oxide, Frank-Starling low, physical training, calcium upload, mitochondrial permeability transition, membrane potential.