Circadian variations of the renin-angiotensin-aldosterone system

Circulating levels of the renin-angiotensin-aldosterone system (RAAS) components showed circadian oscillations in both spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Cardiac gene expression of the RAAS components also showed circadian variations in both SHR and WKY rats. Of interest, the amplitudes of these circadian fluctuations were different between SHR and WKY rats. Cardiac gene expression levels of the RAAS components were increased in SHR compared to WKY rats at many time points (especially during the active phase). The physiologic relevance of the differential circadian rhythms of circulating and cardiac gene expression levels of the RAAS components remains to be elucidated.