title: Formation of serotonin by rat kidneys in vivo.
abstract: Renal formation of serotonin by decarboxylation of its amino acid precursor L-5-hydroxytryptophan (L-5-HTP) has been demonstrated with renal tissue homogenates and isolated perfused rat kidneys. Our objective in the present study was to determine whether the conversion of L-5-HTP to serotonin was associated with functional changes by kidneys in vivo. Renal clearance studies were conducted in anesthetized, volume-expanded male Sprague-Dawley rats receiving either saline (n = 9) or L-5-HTP (15 and 75 micrograms/min iv, n = 9). No change in mean arterial pressure was measured during infusions of L-5-HTP at either dose, whereas glomerular filtration rate (GFR), as measured by the clearance of inulin, and effective renal plasma flow (CPAH) decreased by 34 +/- 5% (mean +/- SE, P less than 0.001) and 26 +/- 7% (P greater than 0.07), respectively. Urine flow and sodium excretion decreased by 41 +/- 9% (P less than 0.01). Serotonin and 5-HTP were determined in urine and plasma using HPLC. High levels of 5-HTP were present in plasma, but not urine. Urinary serotonin increased in the rats receiving L-5-HTP without concomitant increases in plasma serotonin. More than 20% of the infused L-5-HTP was recovered in the urine as serotonin. The decarboxylase inhibitor carbidopa (20 micrograms/min) markedly reduced urinary serotonin excretion in the rats which received L-5-HTP and reversed the changes in GFR, CPAH, urine flow, and sodium excretion. Infusions of the amino acid precursor of L-5-HTP, L-tryptophan (n = 7), did not alter kidney function or increase plasma or urinary 5-HTP or serotonin levels. These results are consistent with the intrarenal formation of serotonin by renal decarboxylase with attendant alterations in renal hemodynamics and salt and water excretion.
mesh_terms: D006916:5-Hydroxytryptophan / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D001794:Blood Pressure / Q000187:drug effects; D002230:Carbidopa / Q000494:pharmacology; D004231:Diuresis / Q000187:drug effects; D005919:Glomerular Filtration Rate / Q000187:drug effects; D007668:Kidney / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009318:Natriuresis / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012079:Renal Circulation; D012701:Serotonin / Q000096:biosynthesis* / Q000652:urine
chemical_list: D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D012701:Serotonin; D006916:5-Hydroxytryptophan; D002230:Carbidopa