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Am J Physiol Regul Integr Comp Physiol (December 8, 2005). doi:10.1152/ajpregu.00703.2005
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Submitted on October 3, 2005
Accepted on December 3, 2005

Altered Circadian Rhythm Reentrainment to Light Phase Shifts in Rats With Low Brain Angiotensinogen

Luciana A Campos1, Ralph Plehm2, Jose Cipolla-Neto3, Michael Bader2, and Ovidiu C Baltatu1*

1 Max-Delbruck-Center for Molecular Medicine (MDC), Berlin, Germany; Institute of Research and Development, University of Paraiba Valley (UNIVAP), Sao Jose dos Campos, Brazil
2 Max-Delbruck-Center for Molecular Medicine (MDC), Berlin, Germany
3 Department of Physiology, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil

* To whom correspondence should be addressed. E-mail: ocbaltatu{at}univap.br.

In this study we aimed at investigating the adaptation of blood pressure (BP), heart rate (HR) and locomotor activity (LA) circadian rhythms to light cycle shift in TGR(ASrAOGEN) rats with a deficit in brain angiotensinogen. BP, HR and LA were measured by telemetry. After baseline recordings (bLD), the light cycle was inverted by prolonging by 12-h the light and thereafter the dark period, resulting in inverted darklight (DL) or light-dark (LD) cycles. To the end, a 24-h dark was maintained for 14 days (free-running conditions). When light cycle was changed from bLD to DL, the acrophases (peak time of curve fitting) of BP, HR and LA shifted to the new dark period in both SD and TGR(ASrAOGEN) rats. However, the readjustment of the BP and HR acrophases in TGR(ASrAOGEN) rats occurred significantly slower in comparison to SD rats. The LA acrophases changed similarly in both strains. When light cycle was changed from DL to LD by prolonging the dark period by 12-h, the reentrainment of BP and LA occurred faster than the previous shift in both strains. The readjustment of the BP and HR acrophases in TGR(ASrAOGEN) rats occurred significantly slower in comparison to SD rats. In free-running conditions, the circadian rhythms of the investigated parameters adapted in TGR(ASrAOGEN) and SD rats in a similar manner. These results demonstrate that the brain RAS plays an important role in mediating the effects of light cycle shifts on the circadian variation of BP and HR. The adaptive behavior of cardiovascular circadian rhythms depends on the initial direction of light-dark changes.






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