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

Abstract

Atropine induced various changes in the heart rate in intact rats of various ages. In sympathectomized animals, changes in heart rate variability were less pronounced. Atropine blocked the inhibition of cardiac activity induced by electrical stimulation of the vagus nerve.Key Words: rat; heart rate; sympathectomy; atropine," vagus nerve Vagotomy sharply increases heart rate (HR) in dogs and cats [7]. Atropine, a nonspecific muscarinic receptor (MR) blocker, induces similar effects [2,8,9,11]. Experimental data suggest that the vagus nerves induce tonic effects on the chronotropic heart function. At the same time, some authors believe that the vagus nerves induce no inhibitory effects [6,9], and acceleration of HR after vagotomy and atropine administration is due to excitation of the sympathoadrenal system. Low doses of atropine cause bradycardia, but not tachycardia [10,11]. HR reactions to vagotomy and atropine considerably differ in various animal species [8]; postvagotomy tachycardia is least pronounced in small rodents [5]. Therefore, the effects of atropine on HR in rats are of considerable interest.The population of MR is heterogeneous [ 12]. 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.Department of Anatomy, Physiology, and Health Care, Kazan State Pedagogical University MATERIALS AND METHODSExperiments were performed on 58 outbred albino rats aging 4, 6, 8, and 20 weeks. Sympathectomy was induced by administration of 10 ml/kg guanethidine sulfate to 36 newborn rats for 28 days. The rats were intraperitoneally narcotized with 25% urethane in a dose of 800 mg/kg. Atropine sulfate in a dose of 0.6 mg/kg was injected into the right femoral vein.Stimulation of the right and left vagus nerves (individual parameters for each animal) was performed before and after the injection of atropine at 15-min intervals using an ESL-2 device, Electrocardiogram (ECG) was visually controlled with an Sl-83 oscillograph [ 1 ]. We analyzed 8 of 13 parameters of R-R intervals [4] reflecting activity of the major regulatory mechanisms: mean cardiac interval (Xm), mode (M), mode amplitude (MA), variational range (AX), mean deviation (8), strain index, and HR.The results were analyzed by Student's t test.

Cardiac activity and blood pressure in rats during selective blockade of various subtypes of muscarinic cholinoceptors

“…Previous studies showed that nonselective blockade of muscarinic AChR had no effect on heart rate [2]. Administration of selective antagonists of muscarinic M 1 and M 2 AChR was not accompanied by significant increase in heart rate.…”

“…The short-term decrease in BP after muscarinic AChR blockade reflects the vasoconstrictor effect of acetylcholine. Published data show that administration of atropine prevents bradycardia during electrostimulation of the vagus nerve [2,3]. Selective blockade of 1 of 3 subtypes of muscarinic AChR did not prevent the decrease in HR during stimulation of the right vagus nerve.…”

“…The possibility of immediate and tonic vagal inhibition of cardiac activity in rats was hypothesized [2]. Age-related and interstrain differences in the autonomic regulation of cardiovascular function are probably related to heterogeneity of musarinic AChR in cardiomyocytes and variations in the density and activity of these receptors.…”

M3 cholinergic receptors are involved in postnatal development of cholinergic regulation of cardiac activity in rats

“…It was hypothesized that the chronotropic effect of the vagus nerve includes several components [2,9]. Nonselective blockade of M-ChR with atropine and vagotomy have various effects on the heart [3,6].…”