Secondary Rhythms of Cardiac Activity within Early Ontogenesis: Effects of Blocking of Adreno- and Cholinoreceptors in Rats

The genesis of secondary rhythms in autorhythmic functional systems is analyzed on the example of the spectra of fluctuations of the heart rate observed within early postnatal ontogenesis of rats (from the moment of birth until three weeks old). We studied the effects of blocking of α-adrenoreceptors with phentolamine (5 mg/kg, i.p.), of β-adrenoreceptors with propranolol (1 mg/kg), and of M cholinoreceptors with atropine (1 mg/kg). We concluded that sympathetic influences stabilize the cardiac rhythm in newborn animals, but from the second postnatal week the effects determining generation of secondary rhythms of cardiac activity begin to be mediated by these receptors. Parasympathetic effects on secondary cardiorhythms mediated by M cholinoreceptors are effective even in newborn rats. In rats older than 7 to 8 days, blocking of α-adrenoreceptors and M cholinoreceptors led to the same result, synchronization of the secondary cardiac rhythms. Disorders in the afferent link of the baroreflex arcs after the blockade of α-adrenoreceptors and cessation of transmission in the efferent link of these arcs after blockade of M cholinoreceptors are considered a probable reason for this phenomenon.