Effects of hypoxic factors on cardiac chronotropic reactions in the muskrat Ondatra zibethicus in free behavior |
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Authors: | V I Shereshkov T E Shumilova D A Kuzmin I N Yanvareva A D Nozdrachev |
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Institution: | (1) Ukhtomskii Research Institute of Physiology, St. Petersburg State University, St. Petersburg, Russia |
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Abstract: | Effects of natural and artificial hypoxic factors on cardiac chronotropic reactions were studied in the muskrat Ondatra zibethicus naturally adapted to underwater hypoxia under conditions of free behavior. To record cardiac activity, original implanted
ECG sensors designed in the laboratory were used. Under observations were muskrats in the states of rest, movement, swimming
on the water surface, diving, underwater swimming, forced underwater immersion, and artificial apnea, in the low-pressure
chamber during changes of pressure from 100 to 25 kPa (ascent to an altitude of 11 km) and in the atmosphere of hypoxic mixtures
with 5–10% O2 as well as under conditions of hemic nitrite hypoxia after injection of 3 mg/kg NaNO2. Heart rate (HR) in muskrats is labile and can change within the limits from 15 to 360 beats/min. A characteristic feature
of hypoxic action is development in muskrats of bradycardia that can appear either instantly—both as a conditional reflex
and from the nose lobe receptors—or gradually at a decrease of pO2 in inhaled air. Before diving and after coming to the surface a brief tachycardia can also be observed. The gradual development
of tachycardia takes place in nitrite hypoxia. Development of bradycardia was eliminated at blockade of M-cholinoreceptors
by atropine, and of tachycardia—at blockade of β-adrenoreceptors by propranolol. Blockade of α-adrenoreceptors by phentolamine
did not affect cardiac chronotropic reactions, which indicates the absence of their connection with vasoconstriction. Analysis
of the cardiac rhythm variability has revealed a large spectrum of slow cardiointerval fluctuations connected with animal
functional states. Regulation of cardiac chronotropic reactions in muskrats under effect of hypoxic factors operates along
both sympathetic and parasympathetic pathways of the autonomic nervous system, the leading role in these processes being played
by vagus influences.
Original Russian Text. V. I. Shereshkov, T. E. Shumilova, D. A. Kuzmin, I. N. Yanvareva, and A. D. Nozdrachev, 2006, published
in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2006, Vol. 42, No. 4, pp. 371–377. |
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