Systemic intestinal metabolism of 1-naphthol. A study in the isolated vascularly perfused rat small intestine

Using a vascularly and luminally perfused rat small intestine, we studied the systemic intestinal metabolism of the model substrate 1-naphthol (1-N) to 1-naphthol-beta-D-glucuronide (1-NG). An intestinal extraction ratio of 0.30 +/- 0.02 was found for 1-N. This implies that intestinal metabolism represents up to 14% of the total plasma clearance of 1-N in the rat in vivo. The formed 1-NG was preferentially released into the vascular perfusate, suggesting specialized transport carriers for 1-NG in brushborder and basolateral membrane. When the vascular flow rate was decreased from 10 to 0.5 ml/min, the clearance of 1-N appeared to be completely flow dependent. The apparent conflict between a low extraction ratio (0.30 +/- 0.02 at all flows investigated) and a flow rate-limited 1-N clearance can be explained by the presence of an intestinal vascular bed with a high extraction ratio. We suggest that 1-N is completely extracted from the mucosal blood flow. This view was confirmed by the results of experiments in which the capillary flow of the intestinal mucosa was decreased by infusion of noradrenaline. As a result a temporary decrease in the 1-N extraction ratio was observed. The contribution of the intestine to the total clearance can be masked by the hepatic clearance, because the blood supply to the intestine and liver is coupled in series. An equation was derived to describe the relative contribution of the intestine to the mesenteric clearance of the intestine-liver system. It appears that the effective contribution of the intestine to the mesenteric clearance is of little interest for high extraction drugs.(ABSTRACT TRUNCATED AT 250 WORDS)