Analysis of circadian variation of blood pressure and heart rate in dexamethasone-induced hypertensive rats

We studied the effect of the chronic renal oral administration of dexamethasone (dexa) on arterial blood pressure (BP) in conscious rats. Special attention was paid to the effects of dexa on circadian rhythm of BP. As determined by the tail cuff-method, BP in the dextra-treated group was significantly higher than in the control group 24 h after treatment, then increased gradually, reaching a plateau on the 7th day of treatment. At that time, the difference in BP between the two groups was approximately 30 mmHG. When monitored directly and continuously on day 10, mean arterial pressure (MAP) in the dexa-treated group exceeded that of the control group by approximately 15 mmHg throughout the monitoring period. Thus, the circadian rhythm of MAP was sustained in the dexa-treated group, which was in contrast to the previously reported elimination of circadian rhythm in humans. In addition, the increase in BP may have been overestimated by tail-cuff plethysmography, possibly owing to a hightended cardiovascular reactivity to environmental stimuli in dexa-treated animals.