Decreased plasma and urinary dopamine during dietary sodium depletion in man

This study was designed to investigate the influence of dietary sodium restriction on plasma and urine dopamine levels. Five normal white male volunteer subjects wee studied in metabolic balance at constant 150 meq sodium, 60 meq potassium intake and then daily for 7 days on an isocaloric constant diet of 10 meq sodium and 60 meq potassium/day. With dietary sodium restriction, urinary sodium excretion decreased from 152 +/- 13 meq/day in stepwise fashion to 7 +/- 1 meq/day (P less than 0.001) on day 7. On the first day of dietary sodium restriction, a sodium deficit of 122 meq was associated with a decrease in supine plasma dopamine concentration from 58 +/- 10 to 45 +/- 7 pg/ml (P less than values for 2 days but decreased again to 43 +/- 12 pg/ml (P less than 0.05) on day 4 of sodium restriction and remained significantly lower than control on days 5-7 of sodium restriction (P less than 0.01). Supine plasma norepinephrine concentration increased from 193 +/- 34 to 232 +/- 29 pg/ml (P less than 0.05) on day 1 of sodium restriction and remained elevated during each subsequent day of low sodium intake (P less than 0.001). Supine plasma epinephrine concentration was unchanged by sodium restriction. Urinary dopamine excretion decreased from 12 +/- 2 to 8 +/- 1 microgram/h (P less than 0.05) on day 2 of sodium restriction and remained significantly low during each subsequent day of low sodium intake. Urinary norepinephrine was unchanged by sodium restriction. The data indicate a variable decrease in plasma dopamine concentration and a constant decrease in urinary dopamine excretion during the course of dietary sodium restriction in man.