Effects of Exogenous Adenosine on Heart Rate Variability Indices in Newborn Rats

The dynamics of HR variability (HRV), HR, and respiratory rate (RR) under baseline conditions and after intraperitoneal administration of adenosine at a dose of 90 mg/kg was analyzed in rats aged 3 (P3), 16 (P16), and 30 (P30) days. In newborn rats, a prolonged negative chronotropic effect of adenosine was revealed, unlike the transient effect typical of adult animals. It was found that qualitatively different changes in the mechanisms regulating heart rhythm occur between P3-P16 and P30 after exogenous activation of adenosine receptors. Activation of adenosine receptors is accompanied by a significant decrease in parasympathetic influences during the first two weeks and their significant increase by 30 days. During the first month of life, adenosine administration has no significant effects on sympathetic and neurohumoral factors of heart rhythm regulation.