Competing pathways in drug metabolism. I. Effect of input concentration on the conjugation of gentisamide in the once-through in situ perfused rat liver preparation
Sulfation and glucuronidation are two parallel pathways for the metabolism of phenolic substrates. Gentisamide (GAM) was used as a model compound to examine the effects of parallel competing pathways on drug disappearance and metabolite formation in the once-through perfused rat liver preparation. GAM was found to form one glucuronide (GAM-5G) and two sulfate (GAM-2S and GAM-5S) conjugates. These GAM conjugates were biosynthesized in recirculating rat liver preparations, and were isolated by preparative high-performance liquid chromatography. Specific incorporation of 35S-sodium sulfate and (14C)glucose into GAM sulfate and glucuronide conjugates revealed corresponding elution patterns as labeled GAM metabolites. Their identities were characterized by enzymatic and acid hydrolyses and by NMR spectroscopy. Gentisamide-5-sulfate (GAM-5S) and gentisamide-5-glucuronide (GAM-5G) are major metabolites, and gentisamide-2-sulfate (GAM-2S) is a minor metabolite. Single-pass rat liver perfusions were used to examine the effect of stepwise increases/decreases of input GAM concentration (CIn) on the extraction ratio (E) of GAM and formation of metabolites. The E of GAM remained constant (about 0.89) at input concentrations from 0.9 to 120 microM and decreased at CIn greater than 120 microM. Metabolite patterns, however, changed with GAM CIn, even when E was constant at CIn up to 120 microM. GAM-5S was present as the major metabolite of GAM at all GAM CInS in most liver preparations but the proportions of GAM-5S and GAM-2S decreased at increasing CIn; the proportion of GAM-5G, a minor metabolite at low CIn, increased with increasing CIn. Biliary excretion rates at steady state accounted for 5.3 +/- 2.7% (mean +/- S.D.) of the input rate: GAM-5G was the predominant metabolite found.
- Research Organization:
- Univ. of Toronto, Ontario (Canada)
- OSTI ID:
- 6991755
- Journal Information:
- J. Pharmacol. Exp. Ther.; (United States), Vol. 245:2
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
AMIDES
METABOLISM
BILE
BIOLOGICAL PATHWAYS
CARBON 14 COMPOUNDS
ENZYMATIC HYDROLYSIS
LIQUID COLUMN CHROMATOGRAPHY
LIVER
METABOLITES
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
PERFUSED ORGANS
RATS
SULFUR 35
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIOLOGICAL MATERIALS
BODY
BODY FLUIDS
CHEMICAL REACTIONS
CHROMATOGRAPHY
DAYS LIVING RADIOISOTOPES
DECOMPOSITION
DIGESTIVE SYSTEM
EVEN-ODD NUCLEI
GLANDS
HYDROLYSIS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
LYSIS
MAGNETIC RESONANCE
MAMMALS
MATERIALS
NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
RADIOISOTOPES
RESONANCE
RODENTS
SEPARATION PROCESSES
SOLVOLYSIS
SPECTRA
SULFUR ISOTOPES
VERTEBRATES
560300* - Chemicals Metabolism & Toxicology
550501 - Metabolism- Tracer Techniques