DOPA, dopamine, and DOPAC concentrations in the rat gastrointestinal tractdecrease during fasting

The aim of the present study was to test the hypothesis that 3,4-dihydroxyp henylalanine (DOPA) and dopamine (DA) in the gastrointestinal tract are to a large extent of exogenous origin and derived from food. Tissue concentrat ions of norepinephrine (NE), epinephrine (Epi), DA, DOPA, and 3,4-dihydroxy phenylacetic acid (DOPAC), as measured by reverse-phase HPLC with electroch emical detection, were studied in fed and 4-day-fasted Wistar rats as well as in sympathectomized and adrenodemedullated rats. Sympathectomy and adren al demedullectomy decreased tissue concentrations of NE and Epi, respective ly, but had no effect on the level of tissue DOPA. Large amounts of DOPA an d DA were present in the gastrointestinal tract. Fasting decreased DOPA and DA in the stomach and DOPA concentrations in the quadriceps muscle but no concentrations in other organs. DOPAC in the heart decreased both in respon se to sympathectomy and to fasting, whereas DOPAC decreased in plasma after fasting and in skeletal muscle after sympathectomy. We conclude that the f ood content of DOPA and DA is of major importance for the metabolism of DA and, thus, for the dopamine-sulfate content in the gastrointestinal tract a nd in plasma. The decrease in muscle DOPA after fasting may be explained by less insulin being available during fasting for stimulation of DOPA uptake in the muscle depot. DOPAC in the organism seems to be of a dual origin, d erived partly from DA in the food and partly from DA synthesized in sympath etic nerves.