Effects of zinc and essential fatty acid deficiencies on the lymphatic absorption of vitamin A and secretion of phospholipids

Abstract

Effects of zinc (Zn) and essential fatty acid (EFA) deficiencies on the rates of lymphatic absorption of vitamin A and output of phospholipid (LP) were investigated. Twenty male rats were divided into four groups in a 2 × 2 factorial design: (1) Zn and EFA deficient (−Zn−EFA), (2) Zn deficient and EFA adequate (−Zn+EFA), (3) Zn adequate and EFA deficient (+Zn−EFA), and (4) Zn and EFA adequate (+Zn+EFA). At 9 weeks, rats with lymph cannula were infused at 3 mL/hr via an intraduodenal catheter with a triolein emulsion containing 5.4 μCi 3H-retinol ( 3H-ROH). The lymphatic absorption of 3H-ROH was lowered markedly in −Zn rats. 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 +Zn−EFA and 0.98 nmol/hr in +Zn+EFA rats. Dietary EFA alone produced only a mild effect on 3H-ROH absorption. Similarly, the effect of dietary Zn on the lymphatic output of PL was more pronounced than that of EFA. The output of PL was correlated closely with the absorption of 3H-ROH ( r = 0.90). No interaction between dietary Zn and EFA was noted in the lymphatic 3H-ROH absorption or PL output. The lymphatic output of linoleic acid (LA) or arachidonic acid (AA) in −Zn rats was approximately 50% of that in their respective Zn adequate controls. However, the PL output in −Zn rats was not related to the amount of EFAs released in the lymph. Dietary Zn had no effect on the rate of intestinal PL synthesis, as determined by incubating a micellar solution of lysophosphatidylcholine (LPC) and 3H-palmitic ( 3H-PA) or 3H-arachidonic acid ( 3H-AA) in a jejunal loop in situ. Dietary EFA also did not affect the rate of 3H-PA incorporation into PL. However, the rate of 3H-AA incorporation into PL was significantly lower in −EFA rats than in +EFA rats. In −EFA rats, more 3H-AA was distributed in phosphatidylethanolamine and less in phosphatidylcholine, compared with +EFA groups. The findings indicate that Zn deficiency has a pronounced adverse effect on the lymphatic absorption of retinol, with no interactive effect with dietary EFA. The lowering of 3H-retinol absorption in −Zn rats is correlated highly with a decrease in lymphatic PL output. The decreased 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.