High salt intake blunts plasma catecholamine and renin responses to exercise: less suppressive epinephrine in...

Graded physical exercise was associated with a parallel increase in plasma epinephrine and norepinephrine concentrations, and increments in the latter correlated directly with concurrent increases in plasma renin activity, heart rate, and blood pressure as studied in four normal subjects. With a high salt intake, plasma catecholamine levels were lower at each grade of exercise; the norepinephrine-renin response curve was shifted to the right and the norepinephrine-heart rate response curve to the left. In five patients with borderline essential hypertension, after salt loading epinephrine concentrations were higher and their responses during exercise greater than in normal subjects. A high salt intake suppresses the activity of the sympathetic nervous system as well as the renin system but increases cardiovascular responsiveness to pressor hormones. A high dietary salt intake may contribute to elevated concentrations of plasma epinephrine and to its cardiovascular effects in borderline essential hypertension.