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. 2022 Sep 21:5:361-368.
doi: 10.1016/j.crphys.2022.09.006. eCollection 2022.

Sustained hypoxia in mice increases parasympathetic but not sympathetic tone

Juliana R Souza  1 , Mauro de Oliveira  1 , Benedito H Machado  1
Affiliations

Sustained hypoxia in mice increases parasympathetic but not sympathetic tone

Juliana R Souza et al. Curr Res Physiol. .

Abstract

The autonomic profile of mice submitted to sustained hypoxia (SH) was not yet fully evaluated. Herein, we characterized the cardiovascular and autonomic profile of conscious freely moving mice submitted to SH using two sequential experimental protocols to evaluate the parasympathetic and sympathetic tone to the heart and the sympathetic tone to the vascular resistance. In the first protocol the sequence of antagonists was methyl-atropine followed by propranolol and then by prazosin, while in the second protocol the sequence was propranolol followed by methyl-atropine and then by prazosin. In SH the baseline heart rate was significantly lower than in control mice and the antagonism of the parasympathetic and sympathetic tone to the heart in both experimental protocols indicated an increased parasympathetic tone in SH mice and no changes in the sympathetic tone. Antagonism of the sympathetic tone to the vascular resistance with prazosin produced similar changes in arterial pressure in control and SH mice. Altogether these findings support the concept that mice submitted to SH present a significant increase in the parasympathetic but not in the sympathetic tone, which may explain why the baseline arterial pressure was not increased in SH mice.

Keywords: Cardiovascular system; Mice C57BL/6; Parasympathetic tone; Sustained hypoxia; Sympathetic tone.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Baseline cardiovascular parameters of mice from control (n = 15) and SH (n = 15) groups. Representative traces of pulsatile arterial pressure (PAP), mean arterial pressure (MAP) and heart rate (HR) of a control and SH mice (Panel A). Average values of MAP (Panel B) and HR (Panel C) in control and SH groups. ∗ P < 0.05, unpaired t-test.
Fig. 2
Fig. 2
Changes in the cardiovascular parameters in response to the antagonism of the parasympathetic drive to the heart in mice from control (n = 7) and SH (n = 8) groups. Representative traces of changes in pulsatile arterial pressure (PAP), mean arterial pressure (MAP) and heart rate (HR) in response to the antagonism of parasympathetic tone to the heart with methyl-atropine of a control and SH mice (Panel A). Average values of MAP (Panel B) and HR (Panel C) before and after the injection of methyl-atropine in control and SH groups. * Different within the same group (P < 0.05), one-way ANOVA. #Different from control group (P < 0.05), two-way ANOVA.
Fig. 3
Fig. 3
Changes in the cardiovascular parameters in response to the antagonism of the sympathetic drive to the heart in mice from control (n = 7) and SH (n = 8) groups. Representative traces of changes in pulsatile arterial pressure (PAP), mean arterial pressure (MAP) and heart rate (HR) in response to the antagonism of sympathetic tone to the heart with propranolol of a control and SH mice (Panel A). Average values of MAP (Panel B) and HR (Panel C) before and after the injection of propranolol in control and SH groups. * Different within the same group (P < 0.05), one-way ANOVA.
Fig. 4
Fig. 4
Changes in mean arterial pressure (MAP) in response to the antagonism of the sympathetic vasomotor drive in mice from control (n = 7) and SH (n = 8) groups. Representative traces of fall in pulsatile arterial pressure (PAP) and mean arterial pressure (MAP) in response to the antagonism of sympathetic tone to the vessels with prazosin of a control and SH mice (Panel A). Average values of MAP (Panel B) before and after the injection of prazosin in control and SH groups. * Different within the same group (P < 0.05), one-way ANOVA.
Fig. 5
Fig. 5
Changes in the cardiovascular parameters in response to the sequential antagonism of the of the autonomic nervous system to the heart (sympathetic followed by parasympathetic) and to the antagonism of the sympathetic vasomotor drive in mice from control (n = 8) and SH (n = 7) groups. Average values of MAP (Panel A) and HR (Panel B) before and after the injection of propranolol in control and SH groups. Average values of MAP (Panel C) and HR (Panel D) before and after the injection of methyl-atropine in control and SH groups. Average values of MAP (Panel D) before and after the injection of prazosin in control and SH groups. * Different within the same group (P < 0.05), one-way ANOVA. #Different from control group (P < 0.05), two-way ANOVA.
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