Low zinc intake decreases the lymphatic output of retinol in rats infused intraduodenally with beta-carotene.
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 beta-carotene also is altered in zinc-deficient male rats. The absorption of beta-carotene was estimated by determining the amount of retinol appearing in the mesenteric lymph during intraduodenal infusion of beta-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 nM beta-carotene, 565.1 microM triolein, 27.8 kBq 14C-triolein (14C-OA), 72 mg albumin, and 396 microM 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 beta-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 beta-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 beta-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 beta-carotene and hence the nutritional status of vitamin A.
Noh
Sang K
SK
Department of Human Nutrition, Kansas State University, Manhattan, KS 66506, USA.
Koo
Sung I
SI
D000042:Absorption; D000818:Animals; D002250:Carbon Radioisotopes; D004032:Diet; D004386:Duodenum / Q000187:drug effects*; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008196:Lymph / Q000502:physiology; D008208:Lymphatic System / Q000378:metabolism*; D008297:Male; D008643:Mesentery; D010743:Phospholipids / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014304:Triolein / Q000008:administration & dosage; D014801:Vitamin A / Q000378:metabolism*; D015032:Zinc / Q000008:administration & dosage* / Q000097:blood; D019207:beta Carotene / Q000008:administration & dosage*
D002250:Carbon Radioisotopes; D010743:Phospholipids; D019207:beta Carotene; D014801:Vitamin A; D014304:Triolein; D015032:Zinc