title: Ascorbic acid disposition kinetics in the plasma and tissues of calves.
abstract: Kinetic plasma disposition parameters and tissue distribution of ascorbic acid (AA) and dihydroascorbic acid (DHA) were determined in newborn calves. After a radiolabeled AA intravenous administration, the plasma clearance (Cl) was low (40.8 +/- 9.5 ml.kg-1.h-1), the steady-state volume of distribution (Vss) was very high (8.9 +/- 2.2 l/kg), and the AA mean residence time (MRT) was long (230 +/- 85 h). After administration of a 3-g dose of AA, the Cl was high (450 +/- 146 ml.kg-1.h-1), the Vss was low (0.658 +/- 0.236 l/kg), and the MRT was short (1.49 +/- 0.41 h), indicating a strong nonlinearity of AA disposition in calves and the impossibility of preventing scurvy with the use of a loading AA dose. Nonlinearity was explained by the saturation of both kidney reabsorption and tissue uptake. The estimated AA body pool size was 23.1 +/- 6.8 mg/kg. On the basis of a compartmental analysis and actual tissue concentration measurements, it is suggested that the lung (19% of the pool) constitutes a low-capacity but rapidly mobilized pool able to cover an acute need for AA, whereas muscle and liver (40 and 33% of the pool, respectively) are high-capacity AA pools, but slowly mobilized and involved in covering the calf's long-term AA requirements. The average daily AA entry rate over the first 7 days of life was 3.43 +/- 1.16 mg/kg, and it is suggested that the calf is able to synthesize AA at an early stage.
authors.affiliation: Ecole Nationale Vétérinaire de Toulouse, Unité Associée Institut National de la Recherche Agronomique de Pharmacologie et Toxicologie Expérimentales, France.
authors.forename: P L
authors.initials: PL
authors.lastname: Toutain
authors.forename: D
authors.initials: D
authors.lastname: Béchu
authors.forename: M
authors.initials: M
authors.lastname: Hidiroglou
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001205:Ascorbic Acid / Q000097:blood / Q000493:pharmacokinetics*; D002250:Carbon Radioisotopes; D002417:Cattle; D007700:Kinetics; D008168:Lung / Q000378:metabolism; D008433:Mathematics; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D011865:Radioisotope Dilution Technique; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D002250:Carbon Radioisotopes; D001205:Ascorbic Acid