Hypertension and disrupted blood pressure circadian rhythm in Type 2 diabetic db/db mice

Aug 19, 2008American journal of physiology. Heart and circulatory physiology

High blood pressure and disturbed daily blood pressure patterns in type 2 diabetic mice

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Abstract

Systolic, diastolic, and mean arterial pressures were significantly increased by 11, 8, and 9 mmHg respectively in db/db mice compared with controls.

Db/db mice exhibited a disrupted blood pressure circadian rhythm, with no significant dip in average blood pressure during the 12-hour light period compared to the 12-hour dark period.
The duration and intensity of locomotor activity were significantly decreased in db/db mice.
Power and amplitude of the 24-hour blood pressure rhythm were significantly reduced in db/db mice compared to controls.
The timing of the peak blood pressure rhythm (acrophase) was scattered in db/db mice, indicating a loss of regularity.
Dampened oscillations of the clock genes DBP and Bmal1, but not Per1, were observed in the aorta of db/db mice.

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Human Type 2 diabetes is associated with increased incidence of hypertension and disrupted blood pressure (BP) circadian rhythm. Db/db mice have been used extensively as a model of Type 2 diabetes, but their BP is not well characterized. In this study, we used radiotelemetry to define BP and the circadian rhythm in db/db mice. We found that the systolic, diastolic, and mean arterial pressures were each significantly increased by 11, 8, and 9 mmHg in db/db mice compared with controls. In contrast, no difference was observed in pulse pressure or heart rate. Interestingly, both the length of time db/db mice were active (locomotor) and the intensity of locomotor activity were significantly decreased in db/db mice. In contrast to controls, the 12-h light period average BP in db/db mice did not dip significantly from the 12-h dark period. A partial Fourier analysis of the continuous 72-h BP data revealed that the power and the amplitude of the 24-h period length rhythm were significantly decreased in db/db mice compared with the controls. The acrophase was centered at 0141 in control mice, but became scattered from 1805 to 0236 in db/db mice. In addition to BP, the circadian rhythms of heart rate and locomotor activity were also disrupted in db/db mice. The mean arterial pressure during the light period correlates with plasma glucose, insulin, and body weight. Moreover, the oscillations of the clock genes DBP and Bmal1 but not Per1 were significantly dampened in db/db mouse aorta compared with controls. In summary, our data show that db/db mice are hypertensive with a disrupted BP, heart rate, and locomotor circadian rhythm. Such changes are associated with dampened oscillations of clock genes DBP and Bmal1 in vasculature.

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Hypertension and disrupted blood pressure circadian rhythm in Type 2 diabetic db/db mice

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