The proposed studies will utilize new, state-of-the-art radioenzymatic assay methodology to quantify dopamine (DA) and one of its major metabolites, dihydroxyphenylacetic acid (DOPAC), as well as norepinephrine (NE) and its metabolites, dihydroxymandelic acid (DOMA), dihydroxyphenylglycol (DOPEG) and normetanephrine (NM) in blood and urine. These measurements will be applied, under carefully controlled and standardized conditions of study, to normotensive subjects and those with specifically categorized forms of hypertension to examine the hypothesis that renal sodium handling is, in part, regulated by a balance of relative dopaminergic and noradrenergic activity in the kidney. When established in normotensives during dynamic alterations in sodium balance, abnormalities in this relationship will be sought in subjects in whom altered renal handling of sodium is known to be associated with hypertension or predisposition to the development of hypertension. Further studies are propsed to explore the cause-and-effect nature of observed abnormalities, and to develop new therapeutic and diagnostic approaches.