Document Detail

Glycoconjugates as noninvasive probes of intrahepatic metabolism: III. Application to galactose assimilation by the intact rat.
MedLine Citation:
PMID:  3357416     Owner:  NLM     Status:  MEDLINE    
A tracer methodology has been developed for noninvasive assessment of intrahepatic metabolism of administered labeled sugars. In this procedure, we measure the output of the label from the liver in two glycoconjugates derived from hepatic UDP-glucose, namely, glucuronic acid formed through UDP-glucuronic acid and excreted in the urine following acetaminophen administration, and galactose formed through UDP-galactose and then secreted in the carbohydrate portion of glycoproteins in the plasma. Comparison of the distribution of label from various sugar precursors in these end-products can indicate exchanges between hepatic UDP-glucose, UDP-galactose, and UDP-glucuronic acid. In this study we apply the technique to explore whether the enzyme UDP-galactose-4-epimerase catalyzing the step UDP-galactose to UDP-glucose is nonequilibrium and therefore potentially has a regulatory role for utilization of free galactose. The specific activity in the two glycoconjugates was compared when either [1-3H]galactose or [U-14C]glucose was the infused precursor sugar. In rats under a variety of conditions (fasting, oral refeeding, intravenous administration of galactose), label from [1-3H]galactose accumulated in glycoprotein-bound galactose much more than in acetaminophen-bound glucuronic acid, in comparison to label from [U-14C]glucose, demonstrating limitation of the rate of transfer from UDP-galactose to UDP-glucose at the epimerase step. Accordingly, epimerase is suggested to have a regulatory role in the galactose assimilation pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
M K Hellerstein; H N Munro
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Metabolism: clinical and experimental     Volume:  37     ISSN:  0026-0495     ISO Abbreviation:  Metab. Clin. Exp.     Publication Date:  1988 Apr 
Date Detail:
Created Date:  1988-05-23     Completed Date:  1988-05-23     Revised Date:  2003-11-14    
Medline Journal Info:
Nlm Unique ID:  0375267     Medline TA:  Metabolism     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  312-7     Citation Subset:  IM    
USDA Human Nutrition Research Center on Aging at Tufts, Boston, MA 02111.
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MeSH Terms
Blood Glucose / analysis
Carbon Radioisotopes / diagnostic use
Galactose / metabolism*
Glucose / metabolism
Liver / metabolism*
Rats, Inbred Strains
Tritium / diagnostic use
UDPglucose 4-Epimerase / physiology
Uridine Diphosphate Glucose / metabolism
Reg. No./Substance:
0/Blood Glucose; 0/Carbon Radioisotopes; 10028-17-8/Tritium; 133-89-1/Uridine Diphosphate Glucose; 26566-61-0/Galactose; 50-99-7/Glucose; EC 4-Epimerase

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