Influence of picolinic acid on the uptake of 65zinc-amino acid complexes by the everted rat gut.

Three hundred fifty rats were used in three experiments to: 1) validate the everted gut procedure as an in vitro technique for estimating Zn absorption, 2) determine the effect of increasing ratios of picolinic acid (PA) to Zn on Zn absorption and 3) determine the effect of PA on absorption of Zn and amino acid complexes at pH 6, 7 and 8. In the first experiment the time delay between tissue collection with subsequent storage in ice-cold saline and start of tissue incubation was 0, 10, 20 or 30 min. A linear decrease was observed for 65Zn uptake with increasing delay time. Lysine absorption was not affected by delay time. In the second experiment, molar ratios of PA:Zn of 0, .5, 1.0, 1.5, 2.0 and 2.5 with Zn held constant were evaluated. A linear decrease in 65Zn absorption from 65ZnCl2 occurred as the molar ratio of PA to Zn increased. In the third experiment, 0 and 5 molar ratios of PA to a constant Zn level were evaluated using 65ZnCl2, 65Zn-14C-methionine (ZnMet) and 65Zn-3H-lysine (ZnLys) at pH 6, 7 and 8. The addition of PA decreased Zn absorption regardless of Zn source. The data suggest that the Zn sources used were of similar biological value. The data do not support the theory that PA facilitates Zn absorption.