Study of Norepinephrine Levels and Sympathetic Nervous System Activity

Brain and nerve cells communicate with each other by releasing and picking up chemicals called neurotransmitters. Norepinephrine is a neurotransmitter used by part of the nervous system activated during stress called the sympathetic nervous system. The sympathetic nervous system is involved with regulating blood pressure and pulse rate. Researchers believe the level norepinephrine in the blood can be used to measure activity of the sympathetic nervous system. This study is designed to answer important questions about rates of release of norepinephrine into the blood stream, removal of released norepinephrine, and the sympathetic nervous system response to stress. Researchers will attempt to measure levels of norepinephrine and activity of the sympathetic nervous system in patients with high blood pressure, normal patients with family histories of high blood pressure, patients taking drugs that can effect levels of norepinephrine, and patients with diseases or conditions directly affecting the sympathetic nervous system. In order to examine sympathetic nervous system function in neurocardiological disorders and catecholaminergic effects of dietary manipulations or neuropsychiatric drugs, the protocol calls for evaluations of the kinetics of 3H-norepinephrine or 3H-epinephrine in patients with hypertension, dysautonomias, or disorders thought to involve abnormal catecholaminergic function, and in normotensive normal volunteers. Apparent spillover and clearance rates are estimated based on the norepinephrine or epinephrine concentration during the infusion and their steady-state specific activities, under resting conditions and in response to physiological or pharmacological manipulations thought to affect sympathetic outflows.