INTRADUODENAL PHOSPHATIDYLCHOLINE INFUSION RESTORES THE LYMPHATIC ABSORPTION OF VITAMIN-A AND OLEIC-ACID IN ZINC-DEFICIENT RATS

Previously, the lymphatic absorption of retinol was shown to be lowere d markedly in zinc-deficient (ZD) rats, in parallel with a decrease in phospholipid (PL) output. The present study investigated whether an i ntraduodenal infusion of PL would restore the intestinal absorption of vitamin A in ZD rats fed 3 mg of Zn/kg of diet, as compared with a zi nc adequate pair fed (PF) rats fed 31 mg of Zn/kg. Both ZD and PF rats were trained for meal feeding and fed equal amounts of the respective diets twice daily for 5 weeks. Each rat with lymph cannula was infuse d at 3 mL/hr via a duodenal catheter with a triolein emulsion containi ng 5.4 mu Ci H-3-retinol (H-3-ROH) and 70 nmol retinol with or without 40 mu mol phosphatidylcholine (PC). The absorption of H-3-ROH was mea sured by collecting lymph hourly for 8 hr during lipid infusion. When infused with no PC, the absorption of 3H-ROH was significantly lower i n ZD rats beginning at 2 hr. Until it plateaued at 5 hr, the retinol a bsorption in ZD rats occurred at 0.42 nmol/hr, which was about 50% of the rate observed in PF rats. The cumulative absorption of H-3-ROH for 8 hr was 19.0 +/-C 1.4% in ZD and 29.7 +/- 1.6% dose in PF rats. The cumulative PL secretion was 7.5 +/- 1.1 mu mol in ZD and 14.2 +/ 1.1 m u mol in PF rats. Also, the output of PL remained significantly lower at each hourly interval in ZD than in PF rats. The hourly PL output wa s correlated closely with the hourly H-3-ROH absorption (r = 0.80, P < 0.05). When PC was infused, the rate of H-3-ROH absorption and total absorption for 8 hr in ZD rats were restored completely to the PF leve l, with a simultaneous increase in lymphatic PL output. In both ZD and PF rats, the H-3-ROH absorption increased at 0.97 nmol/hr prior to 5 hr and reached a maximum at 3.9 nmol/hr at 5 hr. The PL outputs for 8 hr in ZD and PF rats were 14.6 and 21.6 mu mol, respectively. The lymp hatic output of oleic acid was correlated highly with SH-ROH absorptio n (r = 0.80, P < 0.05). These findings provide the first evidence that a limited supply of PL to the enterocyte is a primary cause of the im paired absorption of retinol and oleic acid in ZD rats. This may be du e to a defect in the biliary secretion of PL into the intestinal lumen . It is postulated that, because of the lack of PL, the enterocyte of ZD rats fails to form chylomicrons, principal carriers of dietary lipi ds and lipid-soluble nutrients.