Plasma free and sulfoconjugated dopamine in man: relationship to sympathetic activity, adrenal function and meals

Peripheral venous plasma free and sulfoconjugated catecholamines, dopamine (DA), noradrenaline (NA) and adrenaline (A) were measured in normal men (n = 6-7) during conditions significantly altering adrenal and sympathoadrenal function (influence of corticotropin, furosemide, hypoglycaemia and clonidine), after dopamine receptor blockade with metoclopramide and after meals. Median (range) basal plasma free DA concentration was 0.13 (0-0.72) nmol/l and median (range) basal plasma conjugated DA concentration was 15.16 (6.34-45.03) nmol/l. Meals increased plasma sulfoconjugated DA markedly from a median value of 14.97 nmol/l during fasting experiments to a median value of 33.01 nmol/l (p less than 0.05). Plasma free DA did not change in the meal experiments. No changes in plasma DA were observed after administration of corticotropin, furosemide, clonidine, and metoclopramide or during hypoglycaemia. The results suggest that plasma sulfoconjugated DA is derived at least in part from the gastrointestinal tract and not from the sympathoadrenomedullary system as hitherto proposed.