Circadian Rhythm of Circulating Aldosterone in Spontaneously Hypertensive Rats 1

Abstract

Circulating levels of aldosterone were measured by radioimmunoassay at hourly intervals during a 24-hr period to establish the diurnal rhythm of this mineralo-corticoid in spontaneously hypertensive rats (SHR). Aldosterone levels exhibited a distinct circadian variation with concentrations reaching a zenith at 2000 hr and a nadir at 1200 hr in male and female SHR. Aldosterone levels in females were consistently greater than males. Nocturnal aldosterone levels were highest in the early morning hours in male and moderately elevated in female SHR. Male SHR have significantly higher blood pressure than female SHR.