Circadian variation in vascular tone and its relation to alpha-sympathetic vasoconstrictor activity

Article Abstract:

Everyone knows from their own experience that many biological processes follow daily rhythms. These circadian rhythms affect virtually all aspects of human physiological function. Curiously, events such as heart attacks, sudden cardiac death, and stroke are also affected by these daily cycles; these events are more common in the early morning hours than other times of the day. Many physiological processes that might play a role in the risk of heart attack or stroke follow circadian rhythms. Fibrinolytic activity, which dissolves clots that might be forming in a critical artery, is less in the morning. Platelet aggregation, often the first step in clot formation, is most likely to occur in the morning hours. Many hormones that might influence the risk of heart attack, such as norepinephrine, are at their highest levels in the morning. A study was conducted to determine if the muscle tone of blood vessels varies similarly in a daily cycle. The tone of a smaller artery influences the resistance to blood flow. It was found that arterial resistance to blood flow was higher in the morning than in the afternoon or evening. Furthermore, the rate of blood flow was found to be lower in the morning than at other times of the day. This circadian rhythm in the resistance of blood vessels could be eliminated by the infusion of the drug phentolamine. This drug causes blood vessels to relax by interfering with alpha-adrenoreceptors, specific hormone receptors in the sympathetic nervous system, which helps regulate blood pressure. This observation suggests that the alpha-adrenergic mechanisms of the sympathetic nervous system are responsible for the diurnal rhythm. This interpretation is strengthened by the observation that sodium nitroprusside, which causes blood vessels to relax by mechanisms unrelated to the alpha-adrenergic mechanisms, has no effect on the circadian rhythm. Arteries clogged by atherosclerosis are especially sensitive to changes in tone, and these daily rhythms of changing vessel tone may contribute to the increased likelihood of heart attack and stroke in the morning. It should be remembered, of course, that the contribution of vessel tone to the increased morning risk of these events does not rule out participation of other mechanisms such as increased platelet aggregability. (Consumer Summary produced by Reliance Medical Information, Inc.)

Heart attack, Stroke (Disease), Stroke, Circadian rhythms, Nervous system, Sympathetic, Sympathetic nervous system, Biological rhythms, Biorhythms, Vasoconstriction

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Calcium-antagonist receptors in the atrial tissue of patients with hypertrophic cardiomyopathy

Article Abstract:

Hypertrophic cardiomyopathy is characterized by an abnormally enlarged and constricted left ventricle, producing many associated symptoms related to abnormal contraction and relaxation of heart muscle. Calcium is involved in the electrophysiology of muscle contraction by its movement across cell membranes. It is suggested that the increased involvement of cardiac muscle cells and the increased calcium concentration resulting from the disease may cause the associated symptoms. Calcium antagonists, which reduce the amount of calcium and beta-receptor antagonists which attach to receptor sites on heart muscle reduce the effect of calcium and offer symptomatic relief. To determine the amount of calcium and calcium- antagonist receptors in heart tissue, samples were removed during heart surgery and evaluated. The examination revealed an increase in the number of calcium-antagonist receptors, justifying the use of calcium antagonist drugs such as verapamil. It is likely that the increase in calcium channels is responsible for the defect in hypertrophic cardiomyopathy.

Research, Analysis, Calcium channels, Cardiomyopathy, Myocardial diseases, Heart enlargement, Heart hypertrophy, Heart cells, Calcium channel blockers, Heart atrium, Radioligand assay, Heart biopsy

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Association between prior cytomegalovirus infection and the risk of restenosis after coronary atherectomy

Article Abstract:

Patients with coronary artery disease who also are infected with cytomegalovirus may be less likely to benefit from angioplasty and atherectomy. These two techniques are used to remove plaque from inside the artery, but the plaque often returns. Researchers tested 75 patients with coronary artery disease for cytomegalovirus infection before surgery. Forty-nine tested positive and almost half had recurring plaque six months after surgery compared to only 8% of those who tested negative.

Cytomegalovirus infections, Arteries, Coronary arteries, Arterial stenosis

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