Influência de mudanças de fase no ciclo claro-escuro sobre o controle autonômico cardíaco de ratos
Introduction: The circadian system has neural projections for the Autonomic Nervous System (ANS), directly interfering with sympathetic-vagal modulation of the cardiovascular system. Disturbances in the circadian system, such as phase changes in light-dark cycle (LD), has been related to the risk...
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| Formato: | Dissertação |
| Idioma: | por |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/20057 |
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| Resumo: | Introduction: The circadian system has neural projections for the Autonomic Nervous System
(ANS), directly interfering with sympathetic-vagal modulation of the cardiovascular system.
Disturbances in the circadian system, such as phase changes in light-dark cycle (LD), has
been related to the risk of development of cardiovascular diseases due to increased
sympathetic tone and reduction o Heart Rate Variability (HRV - RR intervals). Purpose:
Investigate the interaction between Circadian Timing System and cardiac autonomic control
in rats. Materials and methods: We used 18 Wistar rats (♀, age = 139.9 ± 32.1 days, weight
= 219.5 ± 16.2 g), divided into three distinct groups: Control (CG), phase delay of 6h (GDe)
and phase advance of 6h (GAd). Three animals were excluded during data collection
(CG/GDe/GAd - n=5). Telemeters were surgically implanted in each animal for continuous
acquisition of electrocardiographic (ECG) signals (duration of 21 days in the CG and 28 days
in GDe/ GAd). A LD cycle was established 12h: 12h, beginning of light at18:00h and dark at
06:00h. The animals remained in the same CG LD cycle throughout the experimental period,
while, on the 14th day of registration, the GDe and GAd underwent a delay and an advance
in 6h, respectively. Throughout the experimental period, the locomotor activity (LA), the
mean heart rate (mHR) and variables related to iRR [mean RR (mRR), SDNN, RMSSD, LF,
HF and LF/ HF ratio ] were recorded. All data were analyzed in blocks of 3 and 7 days, for
the presence of circadian rhythm, values of Cosinor - mesor, amplitude and acrophase
(paired t test), phase relationship, differences between light and dark (t test independent),
averages every 30 minutes along each time series (two-way ANOVA with post hoc
Bonferroni). The data block B1,M1 and M2 in CG served as benchmarks for comparisons
between series of analysis of the GAT/GAV. Results: We observed circadian rhythmicity in
the variables LA, mRR and mFC(p<0.01). mRR and mFC showed phase relationship with the
LA in all three groups, being less stable in GAd. In the CG, no significant differences
between blocks were found in any of the analyzes(p>0.05). Among the 7 day blocks, there
was a significant reduction in mRR(p=0.04) and mFC(p=0.03) in GDe and significant
reduction in HF mean(p=0.02) in GAd; and between 3 day blocks, a significant increase of
LF/HF(p= 0.04) in the GDe; besides mRR(p=0.03), SDNN(p=0.04), RMSSD (p=0.04), LF
(p=0.01) and HF(p=0.02) significant increase in the GAd. It was found that the differences
between the means of the mRR, LA and mFC in light and dark phases were not significant
after phase changes in some of the blocks/moments (GDe and GAd). No significant results
were found when comparing rhythmic variables means every 30 minutes over the blocks,
except for a significant decrease in mRR at the middle of the dark phase (B2) and the start of
light phase (B3) - (p<0.01). Conclusion: phase advances and delays (6h) altered cardiac
autonomic control in the experimental groups by temporarily HRV decrease. Phase
advances apparently had greater negative interference in this process, in relation to the
phase delays. |
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