Comparative Analysis of Cardiac Effects of α-Adrenoreceptor Stimulation In Vivo and Ex Vivo in Newborn Rats.

The study examined the effects of α-adrenoceptor stimulation on chronotropic function of Langendorff-perfused isolated heart ex vivo and on cardiac chronotropy in vivo in 7-day-old rats. α-Adrenergic receptor agonist A-61603 reduced heart chronotropy only in the whole organism. No chronotropic effects of selective stimulation of α-adrenergic receptors on isolated hearts were observed in ex vivo experiments.

Effect of Neuropeptide Y on Action Potential of Working Right Atrial Cardiomyocytes in Early Postnatal Ontogeny.

The effects of neuropeptide Y (10-10 M) on electrical activity of right atrial cardiomyocytes of rats aging 7, 21, and 100 days were examined in vitro. Neuropeptide Y affected the amplitude-temporal parameters of the action potential in these cells. It decreased the duration of repolarization phase in 7-day-old rats in concentrations of 10 and 10 M, in 21-day-old rats at 10 and 10 M, and in 100-day-old at 10 M.

Effect of If Current Blockade on Newborn Rat Heart Isolated According to Langendorff.

The study examined the effects of hyperpolarization-activated funny current (If) on HR and coronary flow in Langendorff-isolated hearts from newborn rats. Blockade of If current with ZD7288 changed the examined cardiac parameters. The blocker in a concentration of 10 M decreased HR by 26.

Peculiar Aspects in Influence of α-Adrenoceptor Stimulation on Isolated Rat Heart.

The study examined the effect of α-adrenoceptor stimulation with methoxamine on chronotropic function of isolated heart perfused ex vivo according to Langendorff and cardiac chronotropy in vivo. Stimulation of α-adrenoceptors in isolated heart induced gradually developing bradycardia, which progressed during several minutes. Similar stimulation in vivo produced a short-term bradycardia probably terminated by the compensatory influences in the whole organism.

Peculiar Effects of Selective Blockade of α2-Adrenoceptor Subtypes on Cardiac Chronotropy in Newborn Rats.

We studied the effects of selective blockade of various subtypes of α2-adrenoceptors on cardiac chronotropy in newborn rats. This period in rats is characterized by the absence of adrenergic regulation of heart function. Blockade of α2A/D- and α2B-adrenoceptors in 1-weekold rats provoked tachycardia.

Age-related peculiarities of inotropic response of rat myocardium to selective block of M1-cholinoreceptors.

In vitro effect of M1-cholinoreceptor blockade on the cardiac inotropic function was examined in rats aging 1, 3, 6, 8, and 20 weeks. In 1- and 3-week old rat pups, the sympathetic control of the heart has not developed, the age of 7-8 weeks being pubertal. Adult 20-week rats were used as the controls.