The Effects Of Different Dosing Schedule Of Amlodipine On The Circadian Rhythm Of ET-1 And NO In Rat

Object: Biological functions and processes exhibit significant circadian (rhythms with a period of approximately 24hours) and other period rhythms. The cardiovascular system is organized according to an oscillatory pattern, and most cardiovascular functions exhibit circadian changes. The circadian body rhythms are of particular relevance to cardiovascular disease, including hypertension, myocardial infarction, stroke, cardiac arrhythmias, sudden cardiac death, and other cardiac events. In chronotherapy, an understanding of chronobiological variations in disease states and pharmacodynamic properties of drugs is used to optimize prevention and treatment.Studies have confirmed that the level of plasma endothelin(ET), nitric oxide(NO) and the activity of nitric oxide synthase ( NOS ) show circadian rhythms, and their chronobiology characters have closely correlation to the circadian rhythm of cardiovascular diseases. Therefore, thoroughly recognized these kinds of biological rhythm have important significance in deeply understand the relationship between endothelium function and physiological phenomena as well as pathological events in cardiovascular system. It also has important value to improve cardiovascular diseases therapy and decrease malignant heart events. At present, a few authors have studied circadian rhythm of those substances at molecular level. It requires deeply study to the influence of vasoactive substances circadian rhythm under the amlodipine-administrating.Therefore in this study, we investigated the levels and rhythm of ET-1, NO, eNOS in plasma and myocardial tissue and eNOS-mRNA in myocardial tissue in rats under different time of amlodipine-dosing schedules. These studies play a very important role in explaining these vasoactive substances's circadian rhythm under different drug-dosing schedules in molecular level. They can provid a new train of thought for prevention and cure of cadiovascular disease and its complications.Methods: One hundred twenty-eight age-matched male SPRD rats (with body weight 250³00g)were included in this study. They were divided randomly into four groups according to the dosing time: rats that were administrated with amlodipine at 07:00 in the morning were designated as the"MT group"; rats that were treated with amlodipine at 19:00 were designated as the"NT group"; rats that were treated with water at 07:00 in the morning were designated as the"MC group"; rats that were treated with water at 19:00 were designated as the"NC group". The rats those in amlodipine-treated group were gorged 2.5mg·kg^-1·d^-1 amlodipine. Each group includes 32 rats, every group divided randomly into 4 sub-groups(with 8 rats/group). After 4 weeks, we measured ET-1, NO, eNOS and eNOS-mRNA at different time of the same day acrossing 24 hours. Cosinor fitting analysis and zero amplitude test were introduced to analyze the chronobiological features of the indices above. The compare of circadian values among 4 groups was managed based on Analysis of Variance (ANOVA), and p<0.05 was defined as statistically different borderline.Results:1. The levels of ET-1 in plasma and myocardial tissue were significantly lower in MT and NT group than those in MC and NC group(p<0.01). But the differences between MT group and NT group were not significant (p=0.117). It showed that amlodipine could impact the expression of ET-1: amlodipine treated groups could significantly cut down the levels of ET-1 in plasma and myocardial tissue. There were not different between the two groups with different amlodipine dosing schedules.2. The levels of NO, NOS in plasma and myocardial tissue in MT and NT group were significantly higher than those in MC and NC group.3. The expression of eNOS-mRNA in myocardial tissue of MT and NT group were significantly higher than those in MC and NC group.4. Based on cosinor fitting analysis and zero amplitude test, all ET-1, NO, eNOS and eNOS-mRNA showed typical circadian rhythm. The peak value times of ET-1, NO and eNOS in plasma of MC group occurred in turn were 22:28, 10:40, 7:51, of NC group were 22:22, 10:36, 8:40, of MT group occurred in turn were 16:41, 7:28, 4:29, which were earlier than those in MC and NC group. Of NT group were 2:16, 15:50, 12:36, which were later than those in MC and NC group. The amplitudes of ET-1, NO, eNOS in plasma were similar in the four groups. The peak values and amplitudes of ET-1, NO, eNOS and eNOS-mRNA in myocardial tissue were nearly the same of those in plasma. The peak value times of ET-1,NO and eNOS in myocardial tissue of MC group occurred in turn were 01:49, 14:33, 12:37, of NC group were 02:13, 15:03, 12:26, of MT group occurred in turn were 22:23, 10:17, 09:06, which were earlier than those in MC and NC group. Of NT group were 04:46, 20:39, 16:50, which were later than those in MC and NC group.5. Based on cosinor fitting analysis and zero amplitude test, eNOS-mRNA in myocardial tissue of the 4 groups showed typical circadian rhythm. The peak of eNOS-mRNA in myocardial tissue of MC, NC, MT and NT group were 11:41, 11:55, 01:49, and 17:04, respectively. The amplitudes of eNOS-mRNA in myocardial tissue of the 4 groups were similar.Conclusion:1 The expression of ET-1, NO and eNOS in plasma and myocardial tissue of MC and NC group showed significantly circadian rhythm, and so did eNOS-mRNA. 2 The expression of ET-1, NO and eNOS in plasma and myocardial tissue of MT and NT group showed significantly circadian rhythm, and so did eNOS-mRNA. Administrating amlodipine (either morning dose or evening dose) resulted the significantly decreased in the level of ET-1, while th levels of NO, eNOS as well as eNOS-mRNA were significantly raised.3 Administrating amlodipine at different time schedule could be helpful in resuming the circadian rhythm of above indicesThe results mentioned above suggested that, ET-1, NO, eNOS and eNOS-mRNA all showed typical circadian rhythm. Treated with amlodipine might decrease the level of ET-1, and increase the levels of NO and eNOS. Moreover, administrating amlodipine at different time schedule might be helpful in resuming the circadian rhythms of those indices.