Mechanisms of Modulation of Adrenergic Regulation of Spontaneous Activity Rate and Atrial Myocardial Contractility in Early Postnatal Ontogeny in Rats.

We studied combined effect of the ß1,2-adrenoreceptor agonist isoproterenol and the Y1,5 receptor agonist [Leu31, Pro34]neuropeptide Y on the frequency of spontaneous activity and myocardial contractility in 21- and 100-day-old rats. Isoproterenol increased the frequency of spontaneous activity and reduced the main parameters of isometric contraction of the atrial myocardium. When [Leu31, Pro34]neuropeptide Y was added, the frequency of spontaneous activity and the negative inotropic and the positive chronotropic effects of isoproterenol were reduced in 100-day-old rats. In 21-day-olds rats, a tendency to a decrease in the effect of isoproterenol was observed.

Role of Cyclic Nucleotides in the Effect of Hydrogen Sulfide on Contractions of Rat Jejunum.

We studied the role of cyclic nucleotides in the influence of hydrogen sulfide (H2S) donor, sodium hydrosulfide (NaHS, 200 µM), on motor activity of rat jejunum. NaHS reduced spontaneous and carbachol-induced contractions of rat jejunum segment, which suggests that H2S can act through mechanisms involving muscarinic receptor activation. Against the background of a membrane-penetrating non-hydrolyzable cAMP analogue or under conditions of adenylate cyclase blockade, the inhibitory effect of NaHS on the carbachol-induced contractions was maintained. Against the background of elevated cGMP concentration or guanylate cyclase inhibition, the reduction of carbachol-induced contractions upon exposure to NaHS was less pronounced than in control. It was hypothesized that H2S induces relaxation of carbachol-induced jejunum contractions, affecting protein kinase G targets or activating cGMP synthesis.

Adrenoceptors in Dopaminergic Regulation of Rat Myocardial Contractility in Rats During Ontogeny.

The effects of different dopamine concentrations on contractility of myocardium with blocked α- or ß-adrenoceptors were examined in vitro in 21- and 100-day old rats. In myocardial strips with blocked α-adrenoceptors, dopamine (10-5 M) increased the right atrial contractile force. By contrast, this neurotransmitter (10-9-10-5 M) reduced the contractile force of atrial and ventricular strips with blocked ß-adrenoceptors.

[Hemodynamic Status of Prepubertal and Pubertal Hockey Players].

The hemodynamic status of 11-15-year-old hockey players depending on their age and puberty stage were studied and compared with hemodynamic parameters of the control group. It was found that regular muscle training has a dominant effect on the functional state of cardiovascular system (CVS) in prepuberty and puberty. It was proved that in hockey players a decrease in the heart rate (H R) and an increase in the stroke volume (SV) result in a significant increase in systolic blood pressure (SBP) at the age of 11-14 years and a progressive increase in total peripheral vascular resistance (PVR), in contrast to significantly lower values in the control group. The urgent adaptation of CVS to graduated physical activities at the age of 11-13 years leads to an enhancement of vascular spasmodic reactions while SV remains constant. It was found that in adolescent hockey players have consistently high SV and SBP; at the same time, maximal values of HR, cardiac output (CO) and diastolic blood pressure (DBP) were observed at the stages I and II of the puberty period; then, at the stage III, these parameters decrease. I n the control group, hymodinamic status changed in an opposite way. This may be an evidence of the stress effect of physical activities which results in the adaptive reactions of CVS rather than reactions typical of the puberty period.

Adrenal gland hormones in primary school children.

It was found that in 8-9-year-old children, the hormonal part of the sympathoadrenal system more rapidly develops in boys, while the transmitter part develops more rapidly in girls. The androgenic and glucocorticoid function of the adrenal cortex matures earlier in girls. To the end of the school year, excretion of epinephrine and norepinephrine decreased, which attests to the development of fatigue.

[The impact of increased physical exertion on adrenal cortex state and puberty of the boys].

The research of the adrenal cortex (AC) functional state of 11-15-year-old boys-sportsmen, conducted on the basis of free and bound cortisol (Cf, C) daily excretion indicators, as well as their comparative characteristics with the test class boys revealed that the increased physical activities in the form of regular sport trainings have the overwhelming impact on the age dynamic of AC and puberty of the young sportsmen. It is shown that the Cfexcretion of the 12-14-year-old-sportsmen is characterized by the consistently high indices, and by age of 15 it is observed a significant decrease in the setting of high C values. In contrast to the boys that do not go in for sports and cortisol in urine of which is significantly lower (p < 0.05), but for the age of 13 to 15 it is noted its progressive increase (p < 0.05). A relative slowing ofthe boys-sportsmen puberty process (secondary sexual characters development) is revealed, AC glucocorticoid function pubertal transformation of these boys are completed earlier and in a greater degree reflect its adaptive behavior, that provides raise of child's body resistance to increased physical exertion's influence.

Involvement of P2Y(2,4) receptors in the regulation of myocardial contractility in growing rats.

Experiments with R2Y receptor blockers allowed identification of R2Y subtypes mediating the inhibitory effects of uridine triphosphate on myocardial contractility. In 100-day-old animals, the myocardial inotropic response to the administration of uridine triphosphate was mediated by R2Y2 receptors. R2Y4 receptors took part in the realization of negative inotropic response to uridine triphosphate in all age groups, but the most pronounced effects of this substance on myocardial contractility were found in 100-day-old rats. It was found that R2Y receptor blockers PPADS and reagent blue-2 affect amplitude-time parameters of myocardial contractility in rats of various ages.

Inotropic effect of dopamine on rat heart during postnatal ontogeny.

We studied the effect of dopamine in concentrations of 10(-9), 10(-8), 10(-7), 10(-6), and 10(-5) M on contraction strength of isolated myocardial strips from the right atrium and right ventricle of rats aging 21, 42, 56, and 100 days. Dopamine in a concentration of 10(-9) M had a positive inotropic effect in rats of various ages. Increasing the concentration of dopamine to 10(-7)-10(-5) M was accompanied by a negative inotropic effect on the heart.

Effect of cobalt on parameters of the cardiovascular system in elementary school children.

High incidence of cobalt deficiency (89%) was found in 7-8-year-old girls residents of the Republic of Tatarstan. Significant correlations were revealed between parameters of physical development and cardiovascular system and hair cobalt content. These data suggest that positive balance of cobalt is essential for normal growth and development of child's body and function of the cardiovascular system.

[Electron paramagnetic resonance study of nitric oxide production in rat heart during hypokinesia].

By the method of EPR spectroscopy we studied the intensity of nitric oxide (NO) production after modeling of hypokinesia in rats (limitation of moving activity) through analyses of the amount of NO-containing paramagnetic complexes in tissues of heart and liver. Experimental animals were kept during 60 day protracted hypokinesia. NO amount was assessed by the intensity of EPR spectra of complex (DEDTC)2-Fe(2+)-NO. It was established that after 60 day hypokinesia the 2-3 fold increase of NO quantity occured in heart and liver tissues. The application of a nonspecific inhibitor of NO-synthases, L-NAME, in suspended rats led to a decreased NO quantity up to the value more lower than in control. The obtained results show that the main contribution to the increase in the intensity of NO production during hypokinesia belongs to the fermentative pathway of NO production and the formation of NO by nitrite-reductase activity is not enhanced during hypokinesia.

Nitric oxide level in the rat tissues increases after 30-day hypokinesia: studies by electron paramagnetic resonance (EPR) spectroscopy.

Studies by EPR spectroscopy showed that 30-day exposure of rats to augmenting hypokinesia led to a 3-fold increase in nitric oxide (NO) production in the heart and 2-fold in the liver. These results indicated that long-term hypokinesia stimulated NO synthesis.

Reaction of the adrenal cortex to graded exercise in children with different initial tonus of the autonomic nervous system.

It was found that the response of the adrenal cortex to graded bicycle exercise in children depends on the initial autonomic tonus and is adequate to the background excretion level of hormone metabolites. Seven-year-old sympathotonic girls with increased excretion of 17-hydroxycorticosteroids at rest demonstrated the lowest increase in this parameter after exercise in comparison with more pronounced increment in vagotonics with relative low initial level of glucocorticoid metabolites. Enhanced excretion of glucocorticoid metabolites with a decrease in androgens observed in 9-year-old sympathotonic girls attests to predominance of catabolic processes over anabolic ones and low efficiency of switching from muscle exercise to recovery in children.

[Interaction of adrenergic and purinergic receptors in the regulation of rat myocardial contractility in postnatal ontogeny].

ß-Adrenergic receptor agonist isoproterenol and purinergic receptor agonist 2-methylthio-ATP have a positive effect on the myocardial contractile force and show different efficiencies depending on the age of animals. The maximum inotropic effect of agonists on the ventricular myocardial contractility was observed in 21-day-old rat pups. The study of a combined effect of isoproterenol and 2-methylthio-ATP showed that an increase in the sympathetic regulatory effects on the heart of 21-day-old animals, against the background of a high functional activity of ß-adrenergic receptors and P2X receptors of the heart, a combined administration of the agonists led to a mutually complementing effect of an increase in the myocardial contractility.

[Influence of the initial vegetative tone on the condition of haemodynamics of younger schoolboys].

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.

Involvement of P2Y receptors in myocardial contractile activity of rats during postnatal ontogeny.

We studied the effect of uridine 5'-triphosphate in concentrations of 10(-10)-10(-6) M on myocardial contractile activity in 7-100-day-old rats. Analysis of isometric contraction of myocardial strips showed that uridine 5'-triphosphate reduced the strength of myocardial contraction in rats of all age groups. In 21- and 100-day-old rat pups, exogenous uridine 5'-triphosphate produced a stronger inhibitory effect than in 7-day-old animals. The negative inotropic effect of UTP was abolished under conditions of P2Y(4) purinoceptor blockade with reagent blue-2. These data indicate that the effect of UTP on the myocardium is realized via P2Y(4) purinoceptors.

Indicators of trace-element status of children living in rural areas.

The content of essential and toxic elements, except beryllium and mercury, in the hair of examined children (girls aged 7-9 years) is within the biologically acceptable levels set by WHO. The data on the content of essential trace elements suggest that urgent measures aimed at normalization of the elemental status of children are required.

ATP as modulator of carbacholine effect on contractility of rat myocardium in postnatal ontogeny.

We studied combined effect of 2-m-ATP, P(2) receptor agonist, and carbacholine, muscarinic M(2) cholinoreceptor agonist, on contractility of rat myocardium during the postnatal ontogeny. Activation of P(2) receptors can stimulate or attenuate the effects of carbacholine depending on animal age. 2-m-ATP potentiates the inhibitory effect of carbacholine on myocardial contractility in 14- and 100-day-old rats. In 21-day-old rats, activation of P(2) receptors prevented the negative effect of carbacholine on myocardial contractility. Activation of muscarinic M(2) receptors inhibited the inotropic effect of purine in all age groups.

[Purinergic regulation of rat heart function in ontogeny].

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.

[Human sympathoadrenal system and adrenal cortex in prepubertal and pubertal periods].

A complex study of the functional state of the sympathoadrenal system and adrenal cortex in 10-15-year-old children of both sexes was carried out using the indices of daily excretion of adrenaline, noradrenaline, 17-ketosteroids, and 17-hydroxycorticosteroids. A synchronism in the functional activity of the mediator component of the sympathoadrenal system as well as of the androgenic and glucocorticoid functions of the adrenal cortex was observed with age and during pubertal development of children. At the same time, heterochronic maturation was observed in the sex groups: in girls at the age of 10 and 12 years and in boys at the age of 14-15 years. The changes of different direction and intensity in the excretion of the studied hormones and hormonal metabolites were observed in the sex and age groups. A sharp increase in the daily excretion of glucocorticoid metabolites accompanied by a considerable decrease in the age index of noradrenaline secretion was observed in 14- and 15-year-old boys from beginning to end of school year; in addition, an increase in the daily excretion of sex hormones was observed at the age of 15 years. In girls, these indices varied within the age range, which points to a more sophisticated neuroendocrine control of physiological functions in girls during puberty.