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.

[State of adaptive systems of the body in boys aged of 11-15 years in the process of their age development, pubertal maturation and in the dynamics of the school year].

A comprehensive study of the functional state of the sympathoadrenal system (SAS) and adrenal cortex (AC) in boys aged of 11-15 years, was carried out depending on their age, puberty stage and academic year period, on the basis of indices of the daily adrenaline (A), noradrenaline (NA), 17-ketosteroids (17-KS) and 17-oxyketosteroids (17-OKS) excretion. A certain synchronism of the manifestation offunctional activity of the SAS mediator level, glucocorticoid and androgen AC function is determined as boys grow older and during their pubertal changes. At the same time the different dynamics of the studied indices in boys aged of from 14 to 15 years and by the V puberty stage is marked. During the academic year changes of hormone and hormonal metabolite excretion, having a different focus and intensity in the age groups were observed: a significant decrease of age NA excretion and androgen metabolite indices (at 15) of 14 and 15 year-old teenagers at the end of the academic year is found out, against the backdrop of a substantial and long-term increase of glucocorticoids (February, April), with their dangerous catabolic effect on a child's body and their depressing effect on the immune response.

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.

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.

[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.

Role of P2X and P2Y receptors in rat myocardial contractility during ontogeny.

Stable agonist of P2 receptors 2-methylthio-ATP and selective antagonists of P2X and P2Y receptors PPADS and reactive blue-2 were used for evaluation of the role of P2 receptors in positive contractile reaction of atrial and ventricular myocardium in rats. PPADS significantly moderated the effects of 2-methylthio-ATP in 14-, 21-, and 56-day-old rat pups, but potentiated them in 100-day-old rats. Under conditions of reactive blue-2 treatment, the positive effect of the agonist was preserved in the atria and ventricles in all age groups and was age-dependent.

Effect of ATP and its analogs on contractility of rat myocardium during ontogeny.

The effects of P2-receptor agonists on myocardial contractility were examined in rats aging 14-100 days. ATP and its stable analog 2-methylthio-ATP potentiated the contraction force of isolated myocardial strips in a dose-dependent manner. The agonist concentrations producing the positive inotropic effect increased from days 14 to 100 of life. The efficiency of extracellular purines depends on animal age: in 14- and 56-day rats the positive inotropic effects of ATP and 2-methylthio-ATP were similar, while in 100-day rats ATP produced more pronounced effect than 2-methylthio-ATP.

Role of purinoceptors in cardiac function in rats during ontogeny.

Intravenous injection of exogenous ATP (10(-4) M) to rats aging 21, 56, and 100 days increased the heart rate by the 15th sec postinjection. Stable ATP analogue alpha,beta-methylene-ATP in an equimolar concentration increased the heart rate in rats aging 56 and 100 days (by the 15th second after treatment), but had no effect on 21-day-old animals. alpha,beta-Methylene-ATP in a concentration of 10(-7) M increased the heart rate in 21-day-old rat pups, which attests to high sensitivity of P2 purinoceptors. Administration of ATP and alpha,beta-methylene-ATP after treatment with nonselective purinoceptor antagonist suramin did not increase the heart rate in rats of different age groups. Infusion of ATP and its stable analogue after administration of selective P2Y receptor antagonist reactive blue 2 increased the heart rate in rats of different age groups. These changes reflect activation of P2X receptors in the heart.

Age-related differences in the response of blood stroke volume to stimulation of the sympathetic ganglion in rats with beta-adrenoceptor blockade.

Blood stroke volume in rats aging 21 and 56 days decreased during beta-adrenoceptor blockade with propranolol, but increased again by the 15th minute after treatment. Suprathreshold stimulation of the stellate ganglion decreased the stroke volume and increased the heart rate in control animals. Electrical stimulation after beta-adrenoceptor blockade was followed by a further decrease in stroke volume in young rats. In 100-day-old animals this parameter remained unchanged, while the cardiac output improved.

Effect of beta-adrenoceptor blockade on cardiac activity in rats during postnatal ontogeny.

Electrical stimulation of the right stellate ganglion produces a positive chronotropic effect in 21-, 56-, and 100-day-old rats. The response of the heart rate to suprathreshold stimulation increased from the 21st to 100th day. By contrast, during beta-adrenoceptor blockade the heart rate response decreased. The data suggest that the role of beta-adrenoceptor in the regulation of cardiac chronotropic function increased with age.

Effect of electrical stimulation of right stellate ganglion on cardiac function in rats during postnatal ontogeny.

In all examined age groups of rats, the threshold amplitude of stellate ganglion stimulation is higher for the positive chronotropic effect than for the inotropic effect. The stimulation produced a more pronounced effect on stroke volume than on heart rate.

Effect of exogenous ATP on cardiac activity in rats.

In vivo effects of exogenous ATP on cardiac activity were studied on adult rats. Intravenous administration of ATP produced a positive chronotropic effect, but did not affect the stroke volume. This was due to activation of type II purine receptors, rather than due to the influence of ATP hydrolysis products, since P1 receptor agonist adenosine was ineffective. The blockade of beta-adrenoceptors and muscarinic receptors did not modify the positive chronotropic effect of ATP, which indicated that this action was not realized via sympathetic or parasympathetic nerves. ATP applied against the background of atropine blockade produced a 4-fold increase in the variability of heart rate typical of activation of the parasympathetic myocardial regulation.