Longitudinal pattern of enzymatic and absorptive functions in the small intestine of rats after short-term exposure to dietary cadmium chloride

In vitro and in situ findings suggest an impairment of digestive and absorp tive functions in the small intestine by enteral cadmium salts. In the rat, diets with up to 1 mmol Cd/kg are well tolerated, however, so that the imp airment might not be this drastic or compensated by adaptive changes. To el ucidate whether small intestinal functions are altered, we studied the effe ct of dietary cadmium on the longitudinal pattern of mucosal enzymes and th e in vitro uptake of methyl alpha-D-glucoside in the small intestine of fem ale rats. Three groups of rats were employed, a control group and two group s receiving dietary CdCl2 either at 0.3 or 1.0 mmol Cd/kg of diet. Rats wer e killed after 1 week of feeding. The entire small intestine was removed, r insed with ice-cold saline and divided into 12 segments of equal length. Mu cosal scrapings from each segment were used to measure mucosal cadmium leve ls, sucrase, lactase, alkaline phosphatase, glycylleucine-hydrolase, and di amine oxidase activities. Sugar uptake was determined in vitro in all segme nts using everted rings tissue accumulation method. Although cadmium levels in the mucosa were high (>100 ng Cd/mg protein or >100 mu mol Cd/kg WW) mo st enzyme activities were only slightly changed. When significant decreases in activity were detected, they were only observed in the proximal small i ntestine. Sugar uptake was also impaired only in proximal segments, the max imal transport capacity was reduced by approximately 20%. These findings su ggest that cadmium even at dietary levels of 1 mmol/kg do not lead to a dra stic impairment of digestive and absorptive functions in the small intestin e and that in the rat presently observed, mostly proximal impairments are e asily compensated by unaltered distal functions. Certainly, absorption of m icronutrients, for which an impaired proximal function cannot be compensate d, e.g. iron, might be critical in this respect.