Chronobiology international
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The nocturnal worsening of asthma is a common feature of this disease that recently has received extensive investigation. Most recent efforts have focused on the role of circadian biorhythms that could promote a nocturnal increase in airway inflammation, leading to a subsequent increase in airflow obstruction and asthma symptoms. ⋯ Potential mechanisms for such a sleep-related effect could include the supine posture, alterations in sympathetic and parasympathetic "balance," sleep-associated reductions in lung volume, intrapulmonary pooling of blood, and sleep-associated upper airway narrowing, both with and without snoring and obstructive sleep apnea (OSA). These potential contributors to this troublesome phenomenon deserve further consideration when investigating mechanisms of nocturnal asthma.
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Circadian rhythmicity in the hypotensive effects of sodium nitroprusside (SNP) was determined to characterize the rhythmicity in hypotension mediated by nitric oxide (NO) donor in rats. When SNP was infused for 90 seconds every hour for 48 hours and the mean blood pressure was determined automatically by telemetry under light-dark conditions (LD), the degree of SNP-induced hypotension was shown to be minimal at the onset of the dark phase and to have marked circadian rhythmicity. The possible relationship between the circadian rhythm of the sympathetic nervous system (SNS) activity and SNP-induced hypotension was examined under LD conditions. ⋯ The circadian rhythmicity determined by MEM was weakened, but persisted, in constant dark conditions (DD), suggesting partial involvement of endogenously driven circadian rhythms. In conclusion, the hypotensive effect of hourly infused SNP in rats was decreased in the dark phase in LD, especially at the onset of the dark phase, and clearly showed circadian rhythmicity in both LD and DD. The SNP-induced hypotension may be affected by rapid activation of the SNS at the onset of the dark phase in LD, and regulation of the circadian rhythm in SNP-induced hypotension in rats may be affected by both exogenous light stimuli and the endogenous biological clock.
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In 46 female outpatients with android-type obesity, body mass index (BMI) 36.6 +/- 1.0, waist to hip ratio (WHR) > 0.86, and normal glucose tolerance (NGT) who were hypertensive at entry study [blood pressure (BP) > 140/90 mm Hg] and in 10 clinically healthy, nonobese, normotensive women, we evaluated the relationship between BMI, fat mass, WHR, fasting blood glucose, sum of blood glucose levels during oral glucose tolerance test and casual BP levels, 24-h ambulatory BP monitoring (ABP) parameters as the 24-hour mean, day-time mean, night-time mean and, by using a periodic model of cosine regression, MESOR (midline estimating statistic of rhythm), amplitude, acrophase, and baric impact. In android obese women, a negative correlation between ABP levels (day-/night-time, MESOR, and baric impact of systolic BP; night-time and MESOR of diastolic BP) and BMI has been documented. A positive correlation between systolic BP (casual, night-time mean, MESOR, amplitude, and baric impact), diastolic baric impact, and the WHR has been found. ⋯ Our data could suggest that, when enrolling obese subjects, it must be taken into account that obesity is a heterogeneous disorder. There are in fact obese subjects with normal or impaired glucose tolerance, as well as diabetics with moderate to severe obesity and with gynecoid or android-type obesity. In our android obese subjects with NGT, the WHR rather than the BMI was found to be a better predictor of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study Clinical Trial
Can melatonin improve shift workers' tolerance of the night shift? Some preliminary findings.
The pineal hormone melatonin is potentially useful in the treatment of disorders, especially sleep disorders, associated with circadian rhythm disturbance. We have examined its effects on sleep, mood, and behaviour in a double-blind, placebo-controlled study of a small group of police officers working spans of seven successive night shifts. ⋯ Memory scanning speed and perception of mental load were adversely affected. This preliminary study suggests that melatonin has beneficial effects on sleep and alertness, but that its effects on performance need careful evaluation.