Effect of vagotomy on heart rate in intact and sympathectomized rats of different ages

Abstract

A comparative analysis of temporal variations of the heart rate variability after cutting and stimulation of the vagus in sympathectomized and intact rats showed that changes in heart rate after bilateral vagotomy in sympathectomized rats are opposite to those in the controls. It is postulated that postganglionic fibers modulate sympathetic influence on intracardiac parasympathetic neurons.Cutting of the vagus nerve leads to a marked decrease in heart rate (HR) in animals and humans [5], although in small rodents the postvagotomy tachycardia is very mild [4], suggesting that acceleration of cardiac rhythm after vagotomy is due to excitation of the sympathoadrenal system in response to stimulation of afferent nerve fibers within the vagus [8], rather than being caused by interruption of parasympathetic tonic activity. It should be noted that 48% of nerve fibers in rat vagus are sympathetic fibers [2], while the content of afferent nerve fibers in the vagus is 14-to 15-fold higher than that of efferent fibers [10].At the present time, there is controversy over the mechanisms of postvagotomy tachycardia. Some researchers believe that vagotomy leads to a faster HR by activating the sympathetic nervous system [3,8], while others claim that this system is not implicated in the development of postvagotomy tachycardia [7]. Previously, we showed that the initial transient rise of HR is followed by its normalization or even bradycardia. It is impossible to derive any unequivocal conclusion from studies in which the effect of vagotomy on HR in animals with interrupted sympathetic nerve supply after surgical or chemical sympathectomy was investigated [3,7].

Effect of selective vagotomy on inotropic and chronotropic heart function in rats

“…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, 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].…”

Age-related peculiarities of heart rate in intact and sympathectomized rats injected with atropine

“…The ratio between various MR subtypes changes with age probably due to the development of sympathetic cardiac innervation during the postnatal ontogeny [13,14]. Our previous experiments demonstrated age-related peculiarities of HR response to uni-or bilateral vagotomy in intact and sympathectomized animals [3]. Here we studied the role of MR in the development and regulation of HR in intact and sympathectomized rats during the postnatal ontogeny.…”