Low zinc intake decreases the lymphatic output of retinol in rats infused intraduodenally with β-carotene

Abstract

Previously, we have shown that the lymphatic absorption of retinol is significantly decreased in rats fed a low zinc diet. This study was conducted to determine whether the absorption of β-carotene also is altered in zinc-deficient male rats. The absorption of β-carotene was estimated by determining the amount of retinol appearing in the mesenteric lymph during intraduodenal infusion of β-carotene. One group of rats was fed the AIN-93G diet but low in zinc (LZ; 3 mg/kg) and the other was fed the same diet adequate in zinc (AZ; 30 mg/kg). The LZ and AZ rats were trained to meal feed equal amounts of the diets twice daily. At 6 weeks, each rat with lymph cannula was infused via an intraduodenal catheter at 3 ml/h for 8 h with a lipid emulsion containing 65.0 nmol β-carotene, 565.1 μmol triolein, 27.8 kBq 14C-triolein ( 14C-OA), 72 mg albumin, and 396 μmol Na-taurocholate in 24 ml PBS (pH, 6.7). The lymphatic output of retinol over the 8-h period was significantly lower in LZ rats than in AZ rats. The absorption of 14C-OA also was significantly lower in LZ rats. No significant differences were observed between groups in intestinal β-carotene 15,15′-dioxygenase, retinal reductase, and retinal oxidase activities. The findings demonstrate that low zinc intake or marginal zinc deficiency significantly lowers the absorption of β-carotene as estimated by lymphatic retinol output. The results also indicate that the decrease in retinol output in LZ rats is not linked to defects in β-carotene cleavage and subsequent conversion of retinal to retinol in the intestinal mucosa. This study suggests that zinc status is an important factor determining the intestinal absorption of β-carotene and hence the nutritional status of vitamin A.