Changes in heart rate and stroke volume after successive blockade of cardiac adreno- and cholinoceptors were examined on rats of different age. It was established that irrespective of animal age the heart rate remained unchanged under conditions of total adreno- and cholinergic blockade of the heart. Stroke volume under conditions of total adreno- and cholinergic blockade increased with age.
We studied cardiac pumping function in the offspring of rats subjected to swimming exercise and the offspring of untrained rats. The rat pups were adapted for swimming with stepwise increasing load from day 21 to 70 life. At the age of 21 and 70 days, offspring of trained rats showed lower HR and significantly higher stroke volume and cardiac output than offspring of untrained rats. Agonist of 5-HT(2)-receptors α-methyl-5-hydroxytryptamine maleate (30 μg/kg) reduced enhanced stroke volume in trained offspring born by trained mothers. In trained offspring of untrained rats, the agonist had more pronounced effect on HR.
Analysis of amplitude and time parameters of differentiated impedance cardiogram, stroke and minute blood volumes, and heart rate showed that the ascending portion of impedance cardiogram is longer and the descending portion is shorter in rats sympathectomized with guanethidine. This indicates that the cardiac output indices were less affected by sympathetic control.Key words: differentiated impedance cardiogram; stroke volume; minute circulation volume; sympathectomy; developing organism Impedance cardiography has been successfully used to study the cardiac output indices in a developing organism [1,2,8,9]. The ratio of the amplitude of impedance cardiogram to the fast ejection period allows one to evaluate myocardial contractility [4]. Arterial and venous circulation can be separately assessed using a similar analysis of rheographic parameters [5]. Study of rheographic amplitude-temporal relations is useful in the assessment of cerebral blood flow rates [13]. The method of chemical sympatheetomy with guanethidine has been employed as a model to study the sympathetic control in a developing organism, [1,3,[10][11][12]14]. The amplitude and time parameters of differentiated impedance cardiogram (DIC) as well as stroke volume (SV), minute blood volume (MBV), and heart rate (HR) were analyzed in pharmacologically sympathectomized neonatal rats till day 21 and after finishing drug administration until puberty (100 days). Our objectives were to increase informativity of thoracic tertrapolar impedance cardiography more and to reveal possible mechanisms of the cardiac output control. MATERIALS AND METHODSExperiments were performed on random-bred albino rats at the age of 3, 7, 14, 21, 30, 42, 49, 70 and Pedagogic University, Kazan 100 days. The animals were sympathectomized with guanethidine since the birth till the day 21. The drug was administrated in a daily dose 25 mg/kg, intracutaneously [11]. Control animals were given physiological saline. The rats were anesthetized with Nembutal (40 mg/kg) and breathed naturally. Recording of DIC was performed by the method of thoracic tertrapolar impedance cardiography using an RPG-204 device [15].Amplitude and time parameters of DIC were calculated as described previously [4,6]. Temporal parameters of DIC were measured both in absolute (see) and relative units (%). The ventricular blood ejection period (tu) included the fast ejection period (a) and the slow ejection period (b) (Fig. 1). The tu interval was taken as 100%, the parameters a% and b% were calculated as follows: a%=aX 100/tu, b%=bx lO0/tu.Experimental data were statistically processed by Student's t-test and correlation analysis.
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