Intestinal handling of mercury in the rat: implications of intestinal secretion of inorganic mercury following biliary ligation or cannulation

Abstract

Three sets of experiments were carried out to determine if there is an intestinal secretory component in the fecal excretion of administered inorganic mercury. In the first set of experiments the disposition of a nontoxic 0.5-micromol/kg intravenous dose of inorganic mercury was evaluated in control rats and rats whose bile duct had been ligated. Data collected 24 h after the administration of mercuric chloride indicated that some inorganic mercury had moved from the blood across the epithelium into the lumen of the stomach, small intestine, and large intestine. This secretory movement of mercury was most prominent in the small intestine. Interestingly, the renal uptake and accumulation of mercury were diminished significantly in the rats whose bile duct had been ligated. A time-course experiment showed that the maximum amount of secretory movement of mercury into the lumen of the small intestine occurred during the initial 12 h after the injection of mercuric chloride. By the end of 24 h after the injection of mercuric chloride, much of the inorganic mercury secreted in the small intestine appeared to have moved down into the large intestine. In a third experiment, the disposition of mercury was evaluated in control rats and rats who had their bile duct cannulated. The rationale for this third experiment was to study the disposition of mercury under conditions where obstruction of biliary outflow from the liver would not be as much of an issue as with ligation of the bile duct. Evidence for movement of mercury into the lumen of the intestines was also obtained from the rats whose bile duct had been ligated. Eighteen hours after the injection of mercuric chloride the amount of mercury in the luminal compartment of the small intestine was not statistically different between the two groups of rats. Approximately 1.7-2.1% of the administered dose was present in the luminal contents of the small intestine. Decreased renal uptake of mercury was also detected in the rats whose bile duct had been cannulated. The findings from the present study show that when bile flow is obstructed or diverted, clear evidence for secretory movement of mercury into the lumen of the gastrointestinal (GI) tract can be demonstrated. These findings also indicate that the secretory movement of mercury into the lumen of the GI tract is a mechanism that contributes significantly to the pool of mercury that is excreted in the feces.