Chronobiology of blood pressure.

Blood pressure in normal and hypertensive subjects shows circadian variability with the minima during the hours of sleep. The factors influencing blood pressure show circadian variability, in particular, plasma and urinary aldosterone, plasma deoxycorticosterone and urinary sodium (factors implicated in cardiac output), angiotensin II as measured by plasma renin activity, plasma and urinary epinephrine and norepinephrine, and plasma and urinary prostaglandins of the E series (factors implicated in peripheral resistance). Direct causal relationships have not been established. The treatment of hypertensive subjects in relation to the circadian variability is reviewed.