The effect of oral zinc loading on the absorption of 65zinc in the rat.

Seven groups of 8 rats each were orally loaded with zinc, the daily dose varying from 1.8 to 58 mg, corresponding to about 3 to 100 times of their estimated daily intake of zinc. To record the absorption of zinc, the rats were given a single dose of 65Zn. The retention of the isotope was measured in a whole animal counter at regular intervals. The dose of 58 mg was obviously toxic, since half of the animals died within 5 days. The net absorption of zinc in the remaining experimental groups was found to vary from about 7% in the group receiving the smallest loading dose to 1.8% in the group receiving the highest dose. From the absorption values, as determined by extrapolation of semilog retention curves, the total amount of absorbed zinc was estimated. It was found to differ from about 170 micrograms to about 530 micrograms zinc daily, increasing three times as the loading dose was increased 16 times. This discrepancy suggests the existence of regulatory mechanisms of the absorption of zinc from the intestine.