Objective: To study the effect of the ACTH6-9-Pro-Gly-Pro peptide (ACTH6-9-PGP) on the spectral parameters of heart rate variability (HRV) in Wistar rats during short-term exercise. Methods: The study involved 48 Wistar rats. ACTH6-9-PGP was once administered to the animals intraperitoneally at doses of 5, 50, and 500 µg/kg (3 groups of animals) in a volume of 1 ml/kg. Animals of the control group were injected with normal saline in an equivalent volume. Each group included 6 males and 6 females. HRV indicators were recorded using the Physiobelt 2.5.1 complex (Neurobotics, Russia). HRV analysis was performed by spectral parameters: total power of the spectrum of HRV (TP), the total power of the high-frequency component (HF) (ms2 , %), the total power of the lowfrequency component (LF) (ms2 , %), the total power of the very low-frequency component (VLF) (ms2 , %), LF/HF ratio (LF/HF), index of centralization (IC). The cardio signal was recorded 4 times: 1 – after adaptation to the device; 2 – 15 minutes after the injection of the peptide; 3 – after physical activity (2-minute treadmill run), and 4 – after a 15-minute rest. Results: An analysis of the initial values of the HRV indicators made it possible to establish a shift in the spectral characteristics toward the VLF component in the studied groups. Physical activity in the control group caused an increase in the power of HF, LF, and VLF, however, their ratio (VLF>LF>HF) did not change at all stages of the study. A single intraperitoneal injection of the ACTH6-9-PGP peptide at a dose of 5 μg/kg stabilized the HRV parameters at the initial level. The administration of the peptide at a dose of 50 μg/kg and moderate physical activity were accompanied by an increase in the power of HF and LF compared to the initial level. The percentage of frequency components after the exercise was LF>VLF>HF, and in the recovery period, it became VLF>LF>HF. After the administration of the peptide at a dose of 500 μg/kg, an increase in HF and LF, and a redistribution of the frequency components toward LF>HF>VLF were noted. During the recovery period, a decrease in HF, restoration of the percentage of frequency indicators VLF>LF>HF, and an increase in LF/HF and IC were found. Conclusion: A study of the effects of the ACTH6-9-PGP peptide on HRV in Wistar rats showed that a single intraperitoneal injection at a dose of 5 µg/kg promotes adaptation of laboratory animals to physical activity due to the activation of suprasegmental structures, and at doses of 50 and 500 µg/kg – predominant activation of the peripheral segments of the sympathetic and parasympathetic autonomic systems. Keywords: ACTH6-9-Pro-Gly-Pro, heart rate variability, physical activity, Wistar rats, spectral parameters.

In this study, we investigated the heart rate variability (HRV) of awake male and female Wistar rats using a non-invasive technique of electrocardiosignal recording. We established significant differences in the value of HRV indicators in groups of animals differing in spectral parameters (total power of the spectrum (TP), high-(HF) and low-frequency (LF) components of the spectrum). The following HRV indicators were shown to be highly informative: statistical (SDNN — the standard deviation of the complete array of RR intervals, RMSSD — the square root of the standard deviations of successive RR intervals, CV — the coefficient of variation) and spectral (TP, HF, LF, VLF is a very low–frequency component of the HRV spectrum, LF/HF is the vagosympathetic interaction index, IC — centralization index). The data obtained should be taken into account when advancing the existing methodology for studying the pathogenetic mechanisms of HRV changes and determining the prognostic value of these HRV parameters.

Objective: to study the characteristics of heart rate variability in female Wistar rats under conditions of normal wakefulness, moderate physical activity and during recovery. Materials and methods. The study was carried out on 48 female Wistar rats aged 5-6 months. Heart rate variability (HRV) was recorded using Physiobelt 2.5.1 (Neurobotics, Russia). HRV analysis was performed using statistical, geometric, and spectral indicators. Physical activity was created using a two-minute treadmill run at a speed of 15 m/min at an angle of 15°. During the experiment we made 3 records of cardiosignal in each anumal: 1 - before the load, 2 - immediately after the load, 3 - after 15-minute rest. Results. Physical activity led to significant changes in a number of statistical and geometric indexes, but no differences in the spectral indexes of all the records were not found. In this regard, we performed cluster analysis on TP, HF, LF indexes of the record 1 that allowed us to form 2 groups: with low and high spectrum values (LSV and HSV). In each group, we observed significant changes in the values of HRV indexes between the records: in the group with LSV, physical activity led to a change in HR, RRNN, Mo, HF (ms2), LF (ms2, %), VLF (ms2, %), LF/HF, IC, in the group with HSV - HR, RRNN, Mo, Amo, IVR, PAPR, VLF (ms2), LF (%), IC. 15-minute recovery contributed to a further change in the value of HRV parameters. Conclusion. The results of the current study demonstrated that physical activity led to activation of the sympathetic nervous system, mobilization of neurohumoral regulation, as well as a change in the level of regulation of the cardiorhythm from peripheral to the central one. The analysis of HRV parameters in females with LSV and HSV allowed us to establish the features of neurohumoral regulation of the functional state of the organism in groups of animals initially different in spectral characteristics.

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