Do leukocytes have a role in hypertension?

In this issue of Hypertension, Schmid-Schonbein and colleagues investigate the possible role of leukocytes in the pathophysiology of hypertension. The authors measured leukocyte counts and spontaneous leukocyte activation of freshly drawn blood in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Special care was taken to control various factors (source of rats, age, seasonal changes, type of anesthesia) that may influence leukocyte count and function. The total leukocyte count was greater in SHR when compared with WKY rats. Young SHR (4-8 weeks) already showed a 40% higher leukocyte count as controls at a stage when mean blood pressure was near normal values. Spontaneous formation of superoxide anions, as an indicator for leukocyte activation, was more frequent in SHR than WKY rats. Schmid-Schdnbein et al speculate that leukocytes contribute to the pathogenesis of vascular changes and subsequent organ injury in hypertension. Epidemiological studies have shown correlations between an elevated blood leukocyte count and the risk of various cardiovascular diseases such as myocardial infarction and stroke. Leukocyte count has also been shown to correlate with the extent of coronary artery disease observed at coronary angiography. Moreover, recent studies have demonstrated that activation of leukocytes occurs more frequently in patients with intermittent claudication, unstable angina pectoris, and acute myocardial infarction and may be associated with the incidence and severity of ventricular arrhythmias in the early phase of myocardial infarction. It is possible that the elevated leukocyte count and activation is not an epiphenomenon but instead that leukocytes play a central role in the pathogenesis of the diseases mentioned above. It has been suggested that leukocytes may play a key role in the development of atherosclerosis. However, little is known about the role of leukocytes in hypertension. Activated leukocytes may contribute to the