Role of 5-HT(2B) Serotonin Receptor Agonist in the Regulation of Pumping Function of the Heart.

The effect of α-methyl-5-hydroxytryptamine maleate, an agonist of 5-HT2B serotonin receptors, on the pumping function of the heart was examined in rats with forced motor behavior. At rest, swim-trained rats demonstrated lower HR and greater stroke volume and cardiac output than untrained rats. The agonist decreased HR, stroke volume, and cardiac output in 21- and 70-day-old swim-trained rats, but not in 100- and 200-day-old rats.

Regulation of pumping function of the heart in developing body under changing regimens of motor activity.

We analyzed parameters of the pumping function of the heart in rats subjected to enhanced motor activity after a preliminary 70-day hypokinesia under conditions of α- and ß-adrenergic receptor stimulation with norepinephrine followed by blockade of ß-adrenergic receptor with propranolol (obsidian) and α1-adrenergic receptors with doxazosin. After norepinephrine administration, the HR and cardiac output were higher in rats with enhanced physical activity after preliminary hypokinesia than in rats with low physical activity. After propranolol administration, stroke volume and cardiac output in 100-day-old rats with limited activity were lower, and HR higher was than in rats with enhanced physical activity after preliminary 70-day hypokinesia. After administration of doxazosin, rats with limited motor activity demonstrated more pronounced changes in HR than rats with enhanced physical activity after preliminary 70-day hypokinesia.

[Effect of the sharply strengthened motor activity on heart pumping ability of rats and mechanisms of its regulation].

The indicators of heart pumping ability of rats at a muscular loading of the maximum power and also in the conditions of transition from sharply strengthened motor activity regime on a strengthened motor activity regime at adrenergic influence stimulation and blockade were investigated. At rats of 100-daily age at the strengthened motor activity heart rate is less, and blood stroke volume is more, than in the rats, subject to muscular loading of the maximum power. The adrenergic influence on the heart's pumping ability of sharply strengthened motor activity rats is much more, than of unlimited motor activity rats. At the α1-adrenoreceptors blockade at 100-daily rats the decreasing in intensity of muscular loading causes increased in adrenergic influence on heart pumping ability.

Influence of 5-HT(2) receptor agonist on cardiac pumping function of trained offspring of trained rats.

We studied cardiac pumping function in the offspring of rats subjected to swimming exercise and the offspring of untrained rats. The rat pups were adapted for swimming with stepwise increasing load from day 21 to 70 life. At the age of 21 and 70 days, offspring of trained rats showed lower HR and significantly higher stroke volume and cardiac output than offspring of untrained rats. Agonist of 5-HT(2)-receptors α-methyl-5-hydroxytryptamine maleate (30 µg/kg) reduced enhanced stroke volume in trained offspring born by trained mothers. In trained offspring of untrained rats, the agonist had more pronounced effect on HR.

Changes in heart rate of rats subjected to treadmill training.

The mechanisms of extracardiac regulation of heart rate were studied in rats subjected to muscle training on a treadmill with different slope angle (0 degrees , 5.5 degrees up, and 5.5 degrees down). Muscle training on a treadmill sloping down was optimal for the development of training bradycardia in 70-day-old rats.

Pumping action of the heart in rat pups subjected to muscle training at different terms of postnatal ontogeny.

Experiments performed on random-bred rat pups showed that muscle training during earlier terms of postnatal ontogeny produce more pronounced changes in the pumping function of the heart.

Changes in stroke volume in rat pups during adaptation to various regimens of motor activity.

Experiments on rat pups showed that regular exercise for 4 weeks starting from day 14 after birth considerably increased stroke volume. Similar dynamics of stroke volume was observed in subsequent period of restraint locomotion. Experimental hypokinesia starting from day 14 after birth significantly limited the age-dependent increase in SV. However, subsequent exercise training promoted the increase in stroke volume in these rats. In trained rats the regulation of stroke volume during hypokinesia remained unchanged, while in restrained rats subsequent training was associated with considerable reduction of sympathetic regulation of stroke volume.

Effect of physical training on sulfamethazine acetylation rate.

We studied the rate of sulfamethazine acetylation in athletes and untrained controls aging 18-22 years. The rate of sulfamethazine acetylation in controls was characterized by a bimodal distribution: rapid and slow acetylators constituted 42 and 58%, respectively. The rate of sulfamethazine biotransformation in athletes was characterized by a trimodal distribution: ultrarapid, rapid, and slow xenobiotic acetylators constituted 48.4, 22.6, and 29%, respectively. The ultrarapid acetylation phenotype was probably associated with N-acetyltransferase induction and reflected adaptation to physical exercises

[Cardiac output in the ontogeny of young rats]. / Serdechnyi vybros v ontogeneze u krysiat.

A differentiated rheogram was recorded in anesthetized rats at the age of 1, 3, 5, 7, 11, 14, 21, 30, 42, 49, 70 and 100 days. Their cardiac output was found to increase with advancing age and played a major part in an increase of the minute-volume output, being more important than the heart rate. The minute-volume of the circulation as related to 100 g body weight proved to be a constant parameter during postnatal ontogenesis. The specific resistance of the blood and the hematocrit increased with advancing age, the dependence of the former on the latter having been expressed by a worked out formula.

[Characteristics of the regulation of the blood stroke volume in rat pups developing under hypokinesia and muscle training]. / Osobennosti reguliatsii udarnogo ob''ema krovi u krysiat, razvivaiushchikhsia v usloviiakh gipokinezii i myshechnoi trenirovki.

In the early postnatal period, high motor activity of young rats leads to an increase in the tonic effects of the sympathetic nerves and to a decrease in that of the vagus on the systolic blood volume.

[Effect of hypokinesia and muscle training on catecholamine levels of the myocardium of rats in postnatal ontogeny]. / Vliianie gipokinezii i myshechnoi trenirovki na kontsentratsiiu katekholaminov v miokarde krys v postnatal'nom ontogeneze.

Following muscular training and hypokinesia in postnatal ontogenesis (10 weeks) rats were examined by fluorometry for the content of catecholamines at rest and after extreme exertion (swimming). Regular muscular training led to an increase in catecholamine concentration in the myocardium. Hypokinesia decelerated catecholamine accumulation by the myocardium. A single extreme swimming exercise brought about a decrease in catecholamine concentration in the myocardium. The minimal adrenaline concentration was the same, being equal to 0.04 microgram/g crude tissue whatever the age and locomotion pattern.

[Catecholamine content in the adrenals of rats developing under hypokinesia and muscle training]. / Soderzhanie katekholaminov v nadpochechnikakh krys, razvivaiushchikhsia v usloviiakh gipokinezii i myshechnoi trenirovki.

The effect of muscle training and hypokinesia on the content of catecholamines in the adrenals of rats in the postnatal ontogenesis has been studied. A systematic swimming training promotes the process of catecholamine accumulation in the adrenals, while hypokinesia slows down that process. An unitary carrying-out of maximum swimming exertion causes a sharp decrease of total content and concentration of catecholamines, at this their minimum concentration in the adrenals of developing animals does not depend on the adaptation to the locomotive regime.