%0 Journal Article
%T Circadian Variations in Blood Pressure, Heart Rate, and HR-BP Cross-Correlation Coefficient during Progression of Diabetes Mellitus in Rat
%A Chikodi N. Anigbogu
%A Daniel T. Williams
%A David R. Brown
%A Dennis L. Silcox
%A Richard O. Speakman
%A Laura C. Brown
%A Dennis G. Karounos
%A David C. Randall
%J International Journal of Hypertension
%D 2011
%I Hindawi Publishing Corporation
%R 10.4061/2011/738689
%X Circadian changes in cardiovascular function during the progression of diabetes mellitus in the diabetes prone rat (BBDP) ( ) were studied. Age-matched diabetes-resistant rats (BBDR) served as controls. BP was recorded via telemetry in contiguous 4£¿hr time periods over 24 hours starting with 12 midnight to 4£¿am as period zero (P0). Prior to onset of diabetes BP was high at P0, peaked at P2, and then fell again at P3; BP and heart rate (HR) then increased gradually at P4 and leveled off at P5, thereby exhibiting a bipodal rhythm. These patterns changed during long-term diabetes. The cross-correlation coefficient of BP and HR was not significantly different across groups at onset, but it fell significantly at 9 months of duration of diabetes (BBDP: 0.39 ¡À 0.06; BBDR: 0.65 ¡À 0.03; ). These results show that changes in circadian cardiovascular rhythms in diabetes mellitus became significant at the late stage of the disease. 1. Introduction Circadian variations in most bodily functions have been recognized. The circadian variation enables the organism, system, and individual organs to maximize efficiency by ensuring optimal performance with minimal energy expenditure. The diurnal variation in blood pressure rhythm has been demonstrated in man [1¨C3] and various mammalian species [4¨C6]. Some variations in the circadian blood pressure patterns have been attributed to endocrine influences [7, 8] while others are thought to be of neural origin [9]. Blood pressure and heart rate are thought to vary in different ways, with diurnal changes in weather, time of day, and temperature. Circadian rhythm involves changes in autonomic function controlled by the hypothalamus and influenced by the higher brain centers. Therefore variation in circadian rhythm may also be an indicator of autonomic changes. Vinik and Erbas [10] have stressed the importance of recognizing and treating autonomic neuropathy in diabetes, but early detection of autonomic neuropathy is difficult with current assessment techniques. The search for more sensitive, less invasive, and less stressful markers of autonomic and cardiovascular dysfunction is still imperative. Young et al. [11] have reported that the heart possesses an internal circadian clock, which is associated with gene expression, metabolism, and contractile performance. They reported loss of synchronization in the phases of these circadian rhythms in streptozotocin-induced diabetes in rats. Loss of circadian rhythm of blood pressure following acute stroke has been reported in human patients [12¨C14]. Diabetes mellitus is known to produce
%U http://www.hindawi.com/journals/ijhy/2011/738689/