EFFECT OF ZINC-DEFICIENCY ON INTESTINAL-ABSORPTION, PLASMA-CLEARANCE,AND URINARY-EXCRETION OF H-3 VITAMIN-A IN RATS

The intestinal absorption and tissue uptake of H-3-retinol (H-3-ROH) w ere examined in zinc-deficient (ZD) rats, as compared with zinc-restri cted (ZR), pair-fed (PF), and ad libitum-fed (CT) controls. Four h aft er gastric intubation of 1.6 mu Ci of H-3-ROH and 22 nmol retinol in 0 .8 ml corn oil, the intestinal absorption was determined by the differ ence between the H-3-ROH dose and the H-3 remaining in the GI tract. T he absorption of H-3-ROH and the H-3 radioactivities appearing in plas ma and liver were significantly lower in ZD rats, with no significant differences in H-3 radioactivities in the kidneys and testes. The plas ma clearance, hepatic uptake, and urinary excretion of H-3-retinyl pal mitate (H-3-ROP) were compared between ZD and PF rats after injecting i.v. a lipid emulsion containing 1.75 mu Ci of H-3-ROP and 10 mu g ret inyl palmitate (ROP). At 10 min, 78.9 +/- 0.7% of the H-3-ROP dose was cleared in ZD rats and 82.6 +/- 3.5% in PF controls, with the half-li ves (t(1/2)) of 4.5 min in ZD rats and 3.9 min in PF rats. The percent dose of the H-3-ROP appearing in the liver at 1 h postdosing also was significantly lower in ZD rats (49.3 +/- 4.3%) than in PF controls (5 7.1 +/- 4.4%). The labeled vitamin A was mobilized from the liver at a slower rate in ZD rats at 1 d. However, at 2 d and thereafter, the H- 3 radioactivity disappeared rapidly from the liver and the H-3 radioac tivity excreted in urine increased. The observations provide evidence for the existence of multiple sites of metabolic interaction between z inc and vitamin A. The impaired intestinal absorption and hepatic mobi lization and increased degradation of the vitamin may be responsible f or the low vitamin A status associated with zinc deficiency. (C) 1995 Wiley-Liss, Inc.