Dose-Dependent Effects of Methoxamine on Myocardial Electrical Activity of Newborn and Adult Rats

This study investigates the effects of the α₁-adrenergic receptor agonist methoxamine at various concentrations (10⁻⁹ to 10⁻⁶ M) on the frequency and characteristics of spontaneous action potentials in right atrial preparations of newborn and adult rats. In newborn rats, methoxamine at all studied concentrations significantly increased the duration of the action potential repolarization phase, while in adult rats, decreasing it. Interestingly, in adult rats, methoxamine at a concentration of (10⁻⁶ M), exhibited a dual effect, decreasing the duration of the action potential repolarization phase in some samples while increasing it in others. Stimulation of α₁-adrenergic receptors by methoxamine in working cardiomyocytes of the right atrium in both age groups led to an increase in the frequency of action potential generation; however, this effect was more pronounced in newborn rats. These findings highlight the age-dependent effects of α₁-adrenergic receptor stimulation on cardiac electrical activity, suggesting that the mechanisms underlying these responses may differ significantly between newborn and adult rats.