title: Excretion and metabolism of nicotinic acid by the avian kidney.
abstract: The renal tubular transport and metabolism of nicotinic acid (NA) were investigated using the Sperber technique in unanesthetized hens. Infusion of [14C]NA into the avian renal portal circulation at 10(-10) mol/kg/min revealed that the 14C label was actively transported into urine at a rate 74% that of simultaneously infused tetraethylammonium. Increases in NA infusion rates enhanced 14C label transport so that it eventually equalled the excretion rate of tetraethylammonium. At a NA infusion rate of 10(-8) mol/kg/min, this transport was not affected by probenecid, pyrazinoic acid or p-aminohippurate. Above infusion rates of 10(-7) mol/kg/min, saturation of 14C label transport was reached. Electrophoretic analysis of the 14C label excreted in urine at NA infusion rates less than 10(-7) mol/kg/min revealed a single, unidentified metabolite. At infusion rates greater than 10(-7) mol/kg/min, both the radiolabeled metabolite and [14C]NA were found in the urine. We conclude that NA is transported by a specific mechanism into the avian tubule cell where it is metabolized. As the body's load of this vitamin increases, NA is excreted first in the form of a metabolite and then as both metabolite and unutilized NA.
authors.affiliation: Department of Pharmacology, State University of New York, Buffalo.
authors.forename: J
authors.initials: J
authors.lastname: Springate
authors.forename: B
authors.initials: B
authors.lastname: Rennick
authors.forename: P
authors.initials: P
authors.lastname: Palumbo
authors.forename: D
authors.initials: D
authors.lastname: Bruckenstein
authors.forename: M
authors.initials: M
authors.lastname: Acara
mesh_terms: D000818:Animals; D001692:Biological Transport; D002645:Chickens; D005260:Female; D006706:Homeostasis; D007684:Kidney Tubules / Q000378:metabolism*; D009525:Niacin / Q000378:metabolism*
chemical_list: D009525:Niacin