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.

[Mechanisms of development of cardiac insufficiency in old age]. / Mekhanizmy razvitiia serdechnoi nedostatochnosti v starosti

Tests conducted with adult (8--10 months) and old (26--28 months) rats brought evidence that in ageing the cardiac ejection, dp/dt max, contractility index, the ATP concentration, that of creatinophosphate, glycogen, pyruvate decline, the phosphorylation coefficient, the lactate content increase, while the level of water-soluble proteins and collagen diminishes and that of water-insoluble ones decreases. In adult rats hemodynamics and myocardial contractility change but unsignificantly on the 4--6th day after coarctation of the aorta, whereas in the old ones there occur functional and metabolic alterations in the heart that are indicative of a developing cardiac insufficiency. The age-specific differences persist also on the 14--16th day following coarctation of the aorta. During these periods the weight of the heart, the content of the myofribrillary proteins and collagen are on the rise, whereas in the old ones the weight of the heart remains unchanged and the level of water-soluble protein drops. Changes in the properties of the actomyosin complex, disruption of the calcium pump, shifts in the system of the energy generation, limitation of potential possibilities incident to the systems of protein biosynthesis in the myocardial cell, all this leads to the development of cardiac incompetence following loading in old age.