THE ROLE OF BETA-ADRENERGIC RECEPTORS IN THE REGULATION OF CARDIAC ACTIVITY IN INTACT AND SYMPATHECTOMIZED GROWING RATS

The research purpose is to study the role of beta-adrenergic receptors in the regulation of cardiac activity in intact and sympathectomized rats of different ages.

Methods and organization of the research. The experiments were carried out on intact and sympathectomized 14-120-day-old heterosexual laboratory rats. Sympathectomy was performed by daily administration of a solution of guanethidine sulfate heated to 38°C at the rate of 10 ml/kg of animal weight for 28 days from birth. The blocker of β-adrenergic receptors obzidan was injected into the femoral vein at the rate of 0.8 mg/kg of animal weight. For the analysis of cardiac activity, an electrocardiogram and a differentiated rheogram were recorded.

Results and their discussion. This series of experiments with the introduction of the non-selective blocker of β-adrenergic receptors obzidan in intact and sympathectomized rats was carried out after vagotomy, which excludes reflex effects and makes it possible to highlight the role of intracardiac regulatory mechanisms in the regulation of the heart. Simultaneous cutting of both vagus nerves (VN) in all studied age groups of intact and sympathectomized animals causes a significant increase in heart rate, which remains higher than the initial indicator at the end of the experiment in all age groups of sympathectomized animals, while in 14-day-old and adult intact rats, this indicator is restored. In control animals, the response of heart rate to obzidan decreases with age. In sympathectomized animals, such dynamics is not observed, which confirms the significant role of β-adrenergic receptors, including intracardiac ones, in the regulation of rat heart activity. 

Conclusion. A pronounced negative chronotropic reaction of the heart to the administration of the non-
selective β-adrenergic receptor blocker obzidan against the background of severed vagus nerves (VN) was registered in all studied age groups of intact and sympathectomized animals, which indicates the important role of β-adrenergic receptors in the regulation of heart rate (HR). A pronounced positive reaction of stroke volume (SV) to the administration of obzidan in both studied groups of animals is manifested from the age of three weeks, which confirms the formation of intracardiac mechanisms regulating the inotropic function of the heart in rats at this age.

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