Reduction of lead toxicity on the kidney and the small intestinal mucosa by kaolin and pectin in the diet

Abstract

The possibility that chemically inert intestinal adsorbents, such as koalin and pectin, may reduce the toxic effects of oral lead poisoning on growth, renal function, and active transport capacity of the jejunum was tested in rats. Seventy-gram rats were fed for 6 weeks diets containing 0.65% of lead (basic) carbonate, with or without a mixture of 4% kaolin and 1% pectin. Corresponding control groups fed cellulose instead of the lead salt were also followed. During the last week of the experiment, quantitative measurements of urinary lead, glucose, and amino nitrogen were carried out, and small intestinal absorptive capacity was determined by an in vivo perfusion technique. The inclusion of kaolin and pectin in the diets prevented growth stunting caused by lead. It also resulted in a greater weight gain in control rats (means ± SEM: 318.8 ± 5.4 g versus 296.5 ± 6.0 g, P < 0.02). However, these additives did not alter lead absorption and urinary excretion of lead, nor did it reduce glycosuria and aminoaciduria in heavy metal poisoning. In the lead-exposed rats, transport capacity for glucose was normalized by kaolin and pectin fed in the diet. These substances also produced a general enhancement of glucose transport capacity in control rats, concomitant with a V_max increase from 0.285 to 0.388 in animals fed lead-containing diets, and from 0.307 to 0.482 mmoles/min × cm in the lead-free groups. There was no change in the K_t affinity constant for glucose (range between 41 and 56 mM), regardless of the kind of diet. Comparable effects were observed for the intestinal absorption rates of sodium, , l-tryptophan, and glycine. No changes were observed in the transport capacity for l-phenylalanine, l-leucine, and α-aminoisobutyric acid by feedings of kaolin and pectin. Ingestion of these substances reduced l-tyrosine absorption. Intake of lead resulted in an elevation of gamma glutamyl-transpeptidase in the small intestinal mucosa. Kaolin and pectin had no specific effect on this enzyme. These findings indicate that two widely used intestinal adsorbents, kaolin and pectin, do not prevent the absorption of lead when fed simultaneously with high doses of the heavy metal. However, they act at the level of the small intestinal mucosa enhancing the absorptive capacity for glucose and certain amino acids, and allowing the rats a normal weight gain despite systemic lead poisoning.