Factors affecting circadian variability

Several unfavorable cardiovascular events show a well-defined pattern in their occurrence throughout the day. Myocardial infarction and ischemia, sudden cardiac death and stroke occur with greater frequency in the morning hours after awakening. Multiple biologic functions such as blood pressure, heart rate, sympathetic neurotransmission, vascular tone, platelet aggregability, and coagulation parameters also show a diurnal variation and appear to contribute to adverse cardiac outcomes. Recent studies have emphasized the importance of 24 h control in decreasing cardiovascular risk. The renin-angiotensin system (RAS), through the important effector peptide, angiotensin II (Ang II), has potent effects on blood pressure, salt and water homeostasis, and target-organ damage. Inhibiting the RAS consequently becomes an important therapeutic avenue for treating hypertension and target-organ damage. Ang II receptor antagonists selectively compete with the binding of Ang II to the Ang II type 1 receptor and, by inhibiting the multiple activities mediated by Ang II at this receptor, may confer cardiovascular benefits additional to that of blood pressure control. Ang II receptor antagonists with an intrinsically long duration of action that produce smooth, sustained antihypertensive activity over the dosing period provide a similar 24 h benefit of Ang II inhibition. Blood Press Monit 5 (suppl 1):S3-S7 (C) 2000 Lippincott Williams & Wilkins.