Early stimulation by estradiol of amino acid penetration in rabbit uterus.

The biochemical events by which estrogen causes rapid growth of the uterus have been investigated principally by studies of the intermediary metabolism or specific enzyme relations within the uterus (1, 2). The tissue-proliferating effect is apparent only after a period of sustained estrogen stimulation whereas the effect of estrogen on the water content and the electrolytes of the uterus is very prompt (3,4). Electrolyte-water relationships and intermediary metabolism have been linked together by the observation that there is a reciprocal relation between the transport of amino acids into cells and the intracellular concentration of the inorganic cations (5). However, studies on the action of estrogen on uterine permeability and its relation to tissue proliferation have been difficult because of the metabolizable nature of most of the available substrates, The demonstration by Christensen (6) that cr-methylamino acids are transported across the plasma membrane in a manner similar to their natural counterparts has led to the development of a-aminoisobutyric acid-l-c” as a tool with which penetration phenomena may be studied without the complication of further metabolism of the substrate (7). Brief communications have reported the utility of cy-aminoisobutyric acid-l-Cl4 in the study of the estrogen-dependent transport process in the uterus (7, 8). The present study extends these observations to the very early effects of estradiol on amino acid transport in uterine tissue.