AMINO-ACID TRANSPORT FROM THE LUMEN OF THE RAT UTERUS

The existence of carrier mechanisms for the uptake of amino acids from the uterine lumen of diestrous and estrogen-primed castrated adult rats was investigated using a technique developed for selective luminal perfusion combined with a dual-label system. After a 30-second luminal perfusion/incubation, ethanol-soluble [14C]-D-mannitol and [3H]-α-aminoisobutyric acid (AIB) were utilized to estimate diffusion and total acid uptake, respectively. The transport component of AIB uptake was considered to be the difference between total AIB and total D-mannitol uptake. The results of this study indicate the presence of a carrier-mediated transport mechanism for AIB which translocates amino acids faster than diffusion, is temperature sensitive, and can be inhibited by high concentrations of unlabeled AIB or natural amino acids (e.g., L-proline, L-threonine, L-leucine, glycine and L-alanine). The pattern of inhibition of AIB transport by the presence of natural amino acids is similar to the carrier mechanism described for the Ehrlich ascites tumor cell. The ability of ouabain to inhibit uterine transport of AIB suggests the dependence of this mechanism on a Na+-K+-activated ATPase. Additionally, the luminal transport mechanism for AIB appears to have a higher affinity for amino acids on the efflux surface than on the influx surface in uteri from-estrogen-primed rats. The transport mechanism described herein may represent a physiological regulation/control mechanism for amino acid levels in the uterine luminal fluid.