Transport of amino acids into the estrogen-primed uterus I. General characteristics of the uptake in vitro

Abstract

The uptake of free amino acids by the immature rat uterus has been studied in vitro. 1. 1. The uptake of the model amino acid, α-aminoisobutyric acid, showed properties of active transport. It was saturable; it occurred against a gradient of the free amino acid; it could be decreased by metabolic inhibitors such as cyanide, 2,4-dinitrophenol and lack of O 2; and it was temperature sensitive. It was also decreased by the presence of high levels of other amino acids or of K +, and by the absence of extracellular Na +. 2. 2. Under appropriate conditions, 1 μg estradiol injected into the rats could increase the uptake in vitro of α-aminoisobutyric acid, l-serine, l-alanine, glycine, l-proline, l-lysine, 1-aminocyclopentanecarboxylic acid, l-valine and dl-norleucine. As short a time as 1 h in vivo was sufficient for this level of the hormone to stimulate uptake of α-aminoisobutyric acid, 1-aminocyclopentanecarboxylic acid, l-alanine and l-proline. A 10 −6 M level of estradiol added in vitro stimulated α-aminoisobutyric acid uptake if incubation periods were extended to 6 h. 3. 3. Estradiol increased uptake at all α-aminoisobutyric acid levels tested (0.3–10 mM). Approximation of kinetic constants showed that the hormone increased the ν max of α-aminoisobutyric acid uptake without altering its K m .