To the Editor:
We have read with great interest the recent review by Angiolillo et al1 that provided an excellent overview of inflammation in acute coronary syndromes, but we were surprised that the authors did not mention light-dark cycles of proinflammatory cytokines.
The implication or association of physiological rhythms with peak activity at a certain time of day or night might be suspected, given that the onset of cardiovascular accidents follows a circadian pattern.2 Several studies suggest that increased cardiovascular mortality in winter might be related to alterations in the biological clock controlled by the suprachiasmatic nucleus. This is regulated by day-night alternations, that is, by light-dark cycles.3,4 Other functions such as cortisol secretion,5 blood pressure variations,6 and vasomotor tone9 also depend on these rhythms.
Our group has shown that interleukin 6 follows a light-dark cycle in patients with acute myocardial infarction.8 These variations can be attributed to the centrally controlled release of this compound by the neuroendocrine system. Such control would be exercised through synthesis and release of melatonin by the pineal gland, which, in turn, is regulated by light-dark variations.9
Although the study of the light-dark variations in proinflammatory cytokines in itself lacks clinical relevance, these findings point the way to new lines of investigation in the field of biological rhythms in humans. More studies will be needed to help clarify the mechanisms that underlie the cyclic nature of the presentation of some acute coronary syndromes. Such knowledge will undoubtedly lead to therapeutic interventions that provide better protection at times of greatest risk.