Mechanisms of neurohumoral regulation of heart function in aging.

Changes in hemodynamics and myocardial contractile capacity following the stimulation of extracardial nerves and administration of various doses of acetylcholine, norepinephrine, propranolol, phentolamin, atropine, serpasil and benzohexonium were studied in albino rats, rabbits and cats of various age. The shifts in cardiac acetylcholine and norepinephrine content and the activity of some enzymes of their catabolism were determined as well. Functional changes were compared with the structural shifts in intramural nervous system. In old animals there was a rise in threshold of voltage, which induced threshold reaction at stimulation of n. vagus and n. sympaticus and there was a change in heart sensitivity to acetycholine and norepinephrine, propranolol, atropine, serpasil and benzohexonium. A relationship was shown between age changes in nervous regulation of heart and transmitter metabolism. The intensity of acetylcholine and norepinephrine synthesis was decreased in old age, the transmitter metabolism in various parts of the heart was not uniformly altered, the sensitivity of epicardial chemoreceptors to nicotine, veratrum, acetylcholine was increased. The reflexes from cardiac mechanoreceptors were diminished.