Bio-clocks and cardiovascular talk: blood pressure meets nature

OTERO-LOSADA M; GRANA DANIEL R; PEREZ-LLORET SANTIAGO; AZZATTO FRANCISCO; MILEI JOSE

Circadian Rhythms: Biology, Cognition and Disorders

Nova Science Publishers, Inc.

Lugar: New York; Año: 2011; p. 347 - 376

Bio-clocks and cardiovascular talk: blood pressure meets nature Matilde E. Otero-Losada1, Daniel R. Grana1, Santiago Pérez Lloret1,2, Francisco Azzato1, José Milei1 1 Instituto de Investigaciones Cardiológicas, “Prof. Dr. Alberto C. Taquini”, Facultad de Medicina, Universidad de Buenos Aires – ININCA-CONICET. Marcelo T. de Alvear 2270, (C1122AAJ), Ciudad Autónoma de Buenos Aires, Argentina 2 Departamento de Fisiología, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, (C1121ABG), Ciudad Autónoma de Buenos Aires, Argentina Biological clocks, mainly circadian clock, developed early in life as an evolutive behavior pertaining to the adaptation of organisms, nearly from algae to mammals, to the cycles of day and night that result from earth´s rotation around its axis. The ubiquity and importance of chronobiological regulation is such that similar mechanisms that govern central clocks are thought to be functional at the cell level in peripheral organs. In that way peripheral clocks may be able to synchronize the activity of the organ with the central ´master´ clock by receiving and sending (feed-back) information. Nearly all behaviors and physiology appear to be somewhat adjusted to the process. Almost all organisms display circadian rhythms, indicating an evolutionary benefit to enable coping with the cyclic nature of the environment. Every day is a new twist on the question of how biological clocks work. Evidence-based experience shows that biological clocks help organize a vertiginous array of biochemical processes in the body. Yet, despite a number of hypotheses, exactly how the microscopic pacemakers in every cell in the body exert such a widespread influence still remains a mystery. High variability in response to a wide variety of stimuli that characterizes blood pressure challenges the reliability of cardiovascular morbidity and mortality predictions based on isolated measures. Only multiple measures over time are acceptable in order to reach meaningful and reliable conclusions according to the present knowledge status. The earliest known account of a circadian process dates from the 4th century BC, when Androsthenes of Thasos described diurnal leaf movements of the tamarind tree (1. Bretzl H. (1903). Botanische Forschungen des Alexanderzuges. Leipzig: Teubner). The first modern observation of endogenous circadian oscillation was made by the French scientist Jean-Jacques d´Ortous de Mairan (1678-1771) who noted circadian movement of the leaves of the plant Mimosa pudica that were not dependent on light-dark cycles [2. De Mairan, JJO. Observation Botanique. Histoire de l´Academie Royale des Sciences, Paris 1729; 35-36). This review compiles, summarizes and discusses specific aspects that characterize the variation of blood pressure over time as suggested by current evidence. Topics contents: 1.       Infradian rhythms (seasonal cycles) in blood pressure. Reports by Pérez-Lloret et al. 2006 (from our Institute), Goodwin et al 2001, Nakajima et al 2000, Brennan et al 1982 and others are contrasted. 2.      Circadian rhythm (a roughly 24-hour cycle comprising early morning surge in blood pressure, diurnal vs nocturnal values, nocturnal dipping behavior, etc.). The papers of White and Larocca 2003, Leary et al 2000, Cavelaars et al 2004, O´Shea and Murphy 2000 and of Pérez-Lloret et al. 2008 and 2006 and Sánchez Gelos et al. 2010 (from our Institute) among others are commented. Discussion evolves around the goal of identifying reliable predictors of risk for cardiovascular disease development. Next, a brief commentary is made on chaos theory and concepts of fractal mathematics in relation with the chronobiologic regulation of blood pressure. Fractal geometry is observed in the physical structure of the vascular tree and the His-Purkinje network of the heart, as in chronophysiological processes, such as heart rate variability. Chaos theory may contribute to broaden our comprehension of time-dependent cardiovascular behavior. Finally, the advantages of chronotherapeutics in the blood pressure–lowering effects of conventional once-a-day antihypertensive drugs are discussed. Chronobiological and chronopharmacological studies are important experimental and clinical approaches to get a deeper insight into the physiological and pathophysiological regulation of the cardiovascular system including their rhythmic organization. Circadian time-dependent clinical studies also provide relevant information to the issue of drug therapy in hypertension. Like as the waves make towards the pebbled shore, So do our minutes hasten to their end; Each changing place with that which goes before, In sequent toil all forwards do contend. Nativity, once in the main of light, Crawls to maturity, wherewith being crown’d, Crooked eclipses ’gainst his glory fight, And Time that gave doth now his gift confound. Time doth transfix the flourish set on youth And delves the parallels in beauty’s brow, Feeds on the rarities of nature’s truth, And nothing stands but for his scythe to mow: And yet to times in hope my verse shall stand, Praising thy worth, despite his cruel hand. Shakespeare’s Sonnet LX