Neuropeptide changes in the suprachiasmatic nucleus in primary hypertension indicate functional impairment of the biological clock

Abnormalities in autonomic activity resulting in disturbances of the diurna l rhythm of many physiologic processes were recently revealed in hypertensi ve patients. These findings suggest deteriorations in the functioning of th e suprachiasmatic nucleus (SCN), which is known to be the biological clock of mammals. To test this hypothesis, we carried out an immunocytochemical s tudy of the SCN of primary hypertension patients who had died due to myocar dial infarction or brain hemorrhage, and compared them with those of indivi duals with a normal blood pressure who had never had any autonomic disturba nces and died from myocardial infarction after chest trauma or from hypothe rmia. We found that the staining for the three main neuronal populations of the SCN; i.e., vasopressin, vasoactive intestinal polypeptide, and neurote nsin, reduced by more than 50% in the hypertensives compared with controls. The present data indicate a serious dysregulation of the biological clock in hypertensive patients. Such a disturbance may cause a harmful hemodynami c imbalance with a negative effect on circulation, especially in the mornin g, when the inactivity-activity balance changes. The difficulty in adjustin g from inactivity to activity might be involved in the morning clustering o f cardiovascular events.