The effect of chronic ingestion of lead on gastrointestinal transit in rats.

GI symptoms such as constipation and abdominal colic are signs of lead poisoning in man, but mechanisms of these effects have not been elucidated. To evaluate GI transit, male Wistar rats were dosed with 1% lead or 0.7% sodium acetate in their diet (AIN-76A). After 7 weeks, lead-treated animals exhibited decreased hematocrit, increased 24-hr urinary excretion of delta-ALA, increased kidney/body weight ratio, and decreased body weight. Blood-lead concentrations were elevated to 196 +/- 57 micrograms/dl. Lead treatment, however, did not result in change in GI transit of a nonabsorbable marker, 51Cr, 15 min or 6 hr after po administration. There was also no change in fecal percentage water content. Since in control animals the semipurified diet AIN-76A markedly decreased fecal excretion rate of 51Cr compared to a cereal-based diet, NIH-07, the latter was used in subsequent experiments. Rats fed 2 or 4% lead acetate in NIH-07 for 8 weeks exhibited renal and hematologic toxicity as in the initial experiment. Weight gain was impaired in the 4% group compared to pair-fed controls. No significant differences were observed in the 1-hr gastric emptying or the fecal excretion of 51Cr in the 2 or 4% lead-treated animals, although there was a trend for slower transit in rats receiving the higher dose. These observations indicate that concentrations of lead sufficient to induce renal and hematologic toxicity in rats do not substantially affect GI transit.