EFFECTS OF ZINC AND ESSENTIAL FATTY-ACID DEFICIENCIES ON THE LYMPHATIC ABSORPTION OF VITAMIN-A AND SECRETION OF PHOSPHOLIPIDS

Effects of zinc (Zn) and essential fatty acid (EFA) deficiencies on th e rates of lymphatic absorption of vitamin A and output of phospholipi d (LP) were investigated. Twenty male rats were divided into four grou ps in a 2 x 2 factorial design: (1) Zn and EFA deficient (-Zn-EFA), (2 ) Zn deficient and EFA adequate (-Zn+EFA), (3) Zn adequate and EFA def icient (+Zn-EFA), and (4) Zn and EFA adequate (+Zn+EFA). At 9 weeks, m rs with lymph cannula were infused at 3 mL/hr via an intraduodenal cat heter with a triolein emulsion containing 5.4 mu Ci H-3-retinol (H-3-R OH). The lymphatic absorption of H-3-ROH was lowered markedly in -Zn r ats. The rates of 3H-ROH absorption in -Zn-EFA and -Zn+EFA groups were 0.44 and 0.58 nmol/hr, respectively, compared with 0.78 nmol/hr in +Z n-EFA and 0.98 nmol/hr in +Zn+EFA rats. Dietary EFA alone produced onl y a mild effect on H-3-ROH absorption. Similarly, the effect of dietar y Zn an the lymphatic output of PL was more pronounced than that of EF A. The output of PL was correlated closely with the absorption of H-3- ROH (r = 0.90). No interaction between dietary Zn and EFA was noted in the lymphatic H-3-ROH absorption or PL output. The lymphatic output o f linoleic acid (LA) or arachidonic acid (AA) in -Zn rats was approxim ately 50% of that in their respective Zn adequate controls. However, t he PL output in -Zn rats was not related to the amount of EFAs release d in the lymph. Dietary Zn had no effect on the rare of intestinal PL synthesis, as determined by incubating a micellar solution of lysophos phatidylcholine (LPC) and H-3-palmitic (H-3-PA) or H-3-arachidonic aci d (H-3-AA) in a jejunal loop in situ. Dietary EFA also did nor affect the rate of H-3-PA incorporation into FL. However, the rate of H-3-AA incorporation into PL was significantly lower in -EFA rats than in +EF A rats. in -EFA rats, more H-3-AA was distributed in phosphatidylethan olamine and less in phosphatidylcholine, compared with +EFA groups. Th e findings indicate that Zn deficiency has a pronounced adverse effect on the lymphatic absorption of retinol, with no interactive effect wi th dietary EFA. The lowering of H-3-retinol absorption in -Zn rats is correlated highly with a decrease in lymphatic PL output. The decrease d PL output is not due to a defect in the intestinal acylation of LPC but probably to impaired biliary secretion of PL into the intestine.