AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 5 1238-R1241, Copyright © 1990 by American Physiological Society
Intestinal absorption and metabolism of ascorbic acid in rainbow trout
R. C. Rose and J. L. Choi
Department of Physiology, University of North Dakota School of Medicine, Grand Forks 58202.
Transport and metabolism of the reduced and oxidized forms of vitamin C
were evaluated in trout intestine in vitro. Transepithelial fluxes of
[14C]ascorbic acid were determined with the substrate present at 10 microM.
The mucosa-to-serosa flux was fourfold greater than the serosa-to-mucosa
flux with ascorbic acid present in both bathing solutions. Cellular
accumulation of the reduced molecule occurred with a final tissue-to-medium
ratio of 1.64. Ascorbic acid influx across the brush-border membrane was
determined under conditions that inhibit transport of other nutrients.
Influx was not reduced because of the presence of the D- or
L-stereoisomeric form of glucose but was highly dependent on the presence
of Na in the bathing medium. Brush-border influx was saturable with a Km of
220 microM. Short-term (8 min) exposure of intestinal loops to the oxidized
form of vitamin C, dehydro-L-ascorbic acid, was followed by
high-performance liquid chromatography analysis of the 14C label present in
the tissue. Total uptake of substrate was greater from the serosal solution
than from the mucosal solution; in either situation most of the 14C label
was found in the reduced state. It is concluded that transport and
metabolic capabilities are present in the trout intestine to absorb
oxidized and reduced forms of vitamin C and to help regulate the redox
potential of circulating ascorbic acid by recycling dehydro-L-ascorbic
acid.
