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The comparative analysis of the functional condition of cardiovascular system and their reaction to the local isometric exercise for the 7-8-year-old boys, who are practically healthy, and in relation ship with the initial tone of the vegetative nervous system is given in the article. By means of variation pulsometer analysis, as well as by means of tetrapolar breast rheography it is found that children with sympathetic influences on heart rate (67.00%-55.55% out of all the studied) in comparison with those, who are normal or vagotonic show the higher activity of neuromediator link in sympathoadrenal system, as well as the increased stroke and minute blood volume on aveioge tachycardia background. With sympathotonic boys it is found that the leadiry link in the mechanism of urgent adaptation of the cardiovascular system to local static exercise there may be the spastic reactions of bloodstream, which allows us to distinguish such-like schoolchildren as a high-risk group in terms of appearance of vegetative dystonia with hypertensire vascular syndrome.

The effect of exogenous ATP and its analogs on heart function was studied in 14-100-day-old rats. Extracellular purines had a positive chronotropic effect on the heart. Intravenous administration of exogenous ATP and its stable analogs induced a dose-dependent increase in heart rate depending on animal age. The analysis of isometric contraction of myocardial strips demonstrated a dose-dependent positive inotropic effect of ATP. The family and subtype of the P2 receptors realizing the positive chronotropic and inotropic effects were identified using selective agonists and blockers. P2X receptors demonstrated the highest sensitivity during early postnatal ontogeny. The age-related pattern of the receptor response to exogenous purines indicated the heterochronic maturation of P2X and P2Y receptors in the myocardium.

In intact rats vagal stimulation reduced heart rate, but had no effect on stroke volume. In sympathectomized animals this treatment decreased both the heart rate and stroke volume. Sympathectomized rats displayed higher sensitivity to vagal nerve stimulation compared to intact animals of the same age (except for rats aging 21 and 56 days).

The guanethidine sympathectomy in 4- and 8-week old white rats increased cardiac sensitivity to acetylcholine. An increase of sensitivity to adrenaline was observed in 8 to 20 weeks of postnatal period. The significance of the changes of extracardiac effects and the cardiac sensitivity to acetylcholine and adrenaline for its chronotropic control in sympathectomized 10-14 week old rats is discussed.