The Influence of Amino Acids and other Organic Compounds on the Gatrointestinal Absorption of Calcium45 and Strontium89 in the Rat

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Abstract
Eighteen amino acids, including those essential for the rat, were assayed for effect on the gastrointestinal absorption of Ca45 and Sr89. The minerals and amino acid were ingested simultaneously; radioassay values for the femur obtained 24 hours after dosage were used as a measure of absorption. L-Lysine and L-arginine were the most potent in promoting mineral absorption, approximately doubling the Ca45 and Sr89 found in the femurs. L-Tryptophan, L-leucine, and L-aspartic acid also produced notable increases. The other amino acids were less effective or ineffective. Lactose produced a greater response than L-lysine and L-arginine. The latter two were more effective in promoting mineral absorption than either gluconate, lactate, citrate, or a mixture of B vitamins. Injection of Ca45 and Sr89 into lysine-treated rats resulted in no increase in radioactivity in the femur while ingestion of both the minerals and lysine produced the usual twofold increase in femur values. The rat preferentially absorbed Ca45 over Sr89 by a factor of about 1.7. Analysis of the Ca*/Sr* ratios in the femurs revealed that most substances were slightly more effective in promoting Sr89 absorption than Ca45 absorption. A dose-response curve of lysine versus femur Ca45 and Sr89 values showed that a molar ratio of lysine:CaCl2 between 1 and 2 was necessary for significant increases in mineral absorption. These findings were discussed in terms of possible mechanisms of action for the stimulatory amino acids.