Significant age-related peculiarities in the dynamics of stroke volume and parameters of variational pulsogram are revealed in bilaterally vagotomized in rats. Asymmetry in vagal influences on cardiac function appear during puberty. Right-sided vagotomy predominantly affects variability of the cardiac rhythm, while left-sided vagotomy mostly affects the force of heart contractions.

The concentrations of acetylcholine and norepinephrine and acetylcholinesterase activity in the myoeardium as well as chronotropic cardiac response to exogenous mediators administered in increasing doses were studied in experiments on growing rats. The results indicate that the chronotropic response to norepinephrine decreases with age despite of increased intracardial concentration of norepinephrine. Cholinergic influence and myocardial reactivity to acetylcholine increase with age.

In intact rats vagal stimulation reduced heart rate, but had no effect on stroke volume. In sympathectomized animals this treatment decreased both the heart rate and stroke volume. Sympathectomized rats displayed higher sensitivity to vagal nerve stimulation compared to intact animals of the same age (except for rats aging 21 and 56 days).

We studied age-related peculiarities of changes in stroke volume, heart rate, and parameters of variational pulsogram after bilateral vagotomy in rats. Positive responses of stroke volume and heart rate to vagotomy appeared on postnatal week 4.

Right-sided vagotomy induced more rapid and pronounced changes in chronotropic indices, while left-sided vagotomy predominantly affected stroke volume. Right-sided, left-sided, and bilateral vagotomy induced similar changes in the variational pulsogram.Key Words: vagus nerve; heart; stroke volume," heart rhythm variability; rat Extracardiac regulation of the cardiac function is provided by sympathetic and parasympathetic influences which are considered as antagonistic, synergic, and compensatory [2,7,9]. Heart response to removal of the parasympathetic influences is species-specific [3,6]. In dogs, the right vagus nerve (VN) regulates the chronotropic, while the left VN controls the inotropic function of the heart [4]. It can be assumed that contraction force and heart rate are regulated by different mechanisms [5]. Therefore, it is of interest to study the tonic influence of contralateral VN on the inotropic and chronotropic heart functions. We studied the dynamics of stroke volume (SV) and parameters of a variational pulsogram after selective vagotomy in rats. MATERIALS AND METHODSExperiments were carried out on 20-week-old outbred albino rats (n=24) anesthetized with intraperitoneal urethan (800 mg/kg, 25% solution). Vagotomy was performed after fixation of the animal on the operation table and VN preparation. In group 1, the right and left VN were cut consecutively with a 60-min interval. In group 2, first the left and then the right VN were cut. In group 3 simultaneous bilateral vagotomy was performed. ECG and differential rheogram were recorded throughout the experiment to analyze heart activity. RESULTSRight-sided vagotomy caused a transient but significant increase in HR and cardiac output (CO) ( Table 1). The most pronounced changes in these indices were observed for the first 5 min. During this period SV showed no significant changes, but then SV and HR decreased.On the contrary, left-sided vagotomy significantly changed SV and only little affected HR (Table 2 ). SV decreased by 9% for the first minute, then increased, and after 5 min exceeded the initial value by 12.4%. It did not return to the baseline within 60 min, while HR decreased after 30 min (p<0.01). Both right-sided and left-sided vagotomy increased the mode amplitude and stress index and decreased the variation amplitude (Table 1, 2). At the same time, the dynamics of SV and HR were different which testifies to the specific effects of the right and left VN on contraction force and HR.Right-sided vagotomy performed after transsection of the left VN increased SV. The increase was most pronounced after 5 min, then SV returned to the initial level (Table 2). HR increased by 3.7% during the first 5 min, then decreased, and after 60 min was 11% below the initial value.