| Summary: | Rat livers were perfused with [15N]glycine and unlabeled sodium benzoate by the single-pass technique via the portal vein or in retrograde fashion via the inferior vena cava. Perfusate [15N]hippurate enrichment was significantly greater than that of hepatic free glycine from 15 to 90 min, regardless of the direction of the perfusion. This result implies that differential labeling by periportal versus perivenous hepatocytes is not likely. When fasted animals were compared to those fed a chow diet or a sucrose-enriched diet, the labeling ratio of medium hippurate/hepatic free glycine decreased by only 9% in spite of a 5-fold decrease in the concentration of intrahepatic free glycine. Administration of nembutal to the intact animal significantly increased the enrichment of medium hippurate by 24% but did not affect the enrichment of the hepatic free glycine. We conclude that the difference between hippurate and free glycine enrichment is related to intracellular compartmentation of glycine transport. We suggest that measurement of the enrichment of hippurate after the administration of [15N]glycine with benzoate in intact animals or human subjects can therefore be used to estimate the enrichment of the intracellular precursor pool of glycine with a correction factor that does not vary appreciably under fed or fasted conditions. When uniformly labeled deuteroglycine was used as the tracer, enrichment of hepatic free glycine was decreased fivefold compared with [15N]glycine. Isotopic enrichments of apoBH and apoBL from the d less than 1.063 g/ml lipoprotein fraction isolated from the perfusion medium between 30 and 90 min averaged 3.7 and 4.1% excess, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
|
|---|
