Diurnal Control of Blood Pressure Is Uncoupled From Sodium Excretion

The diurnal rhythms of sodium handling and blood pressure are thought to be regulated by clock genes, such as Bmal1. However, little is known about the regulation of these factors by Bmal1, especially in rats. Using a novel whole-body Bmal1 knockout rat model (Bmal1^-/-), we hypothesized that time of day regulation of sodium excretion is dependent on Bmal1. Using telemetry to continuously record mean arterial pressure, we observed that male and female Bmal1^-/- rats had significantly reduced mean arterial pressure over the course of 24 hours compared with littermate controls. The circadian mean arterial pressure pattern remained intact in both sexes of Bmal1^-/- rats, which is in contrast to the Bmal1^-/- mouse model. Male Bmal1^-/- rats had no significant difference in baseline sodium excretion between 12-hour active and inactive periods, indicating a lack of diurnal control independent of maintained mean arterial pressure rhythms. Female Bmal1^-/- rats, however, had significantly greater sodium excretion during the active versus inactive period similar to controls. Thus, we observed a clear dissociation between circadian blood pressure and control of sodium excretion that is sex dependent. These findings are consistent with a more robust ability of females to maintain control of sodium excretion, and furthermore, demonstrate a novel role for Bmal1 in control of diurnal blood pressure independent of sodium excretion.