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Amino Acid Transport in Rat Liver and Morris Hepatomas: Effect of Protein Diet and Hormones on the Uptake of -Aminoisobutyric Acid-¹⁴C¹

McArdle Laboratory, Medical Center, University of Wisconsin, Madison, Wisconsin 53706

The uptake of -aminoisobutyric acid-¹⁴C, a nonmetabolizable amino acid, was compared for Morris hepatomas 5123C, 7800, 9633, and 9618A with that of host and normal liver from rats on controlled feeding regimens. The effect of the dietary protein level, hydrocortisone, and glucagon treatment and adrenalectomy on the uptake of the amino acid by the individual hepatomas and liver was also examined. The purpose of this study was to ascertain whether alterations occurred in the amino acid transport system of the hepatomas and to explore the possibility that transport changes might provide an explanation for the diversity in the activity of amino acid metabolizing enzymes reported for these tissues.

Uptake of -aminoisobutyric acid-¹⁴C by Hepatoma 7800 was as great as that of the host liver despite the limited circulation of the hepatoma. A diversity in the concentrative capacity of the amino acid was observed for the hepatomas studied. The uptake by Hepatoma 5123C was 4- to 5-fold greater than host and normal livers, while Hepatoma 7800 showed an uptake about twice that of liver. Hepatoma 9633 showed the same uptake as the host and normal livers, while Hepatoma 9618A showed one-fourth the uptake of liver.

The effect of adrenalectomy on the uptake by Hepatoma 5123C showed a complex relationship to the dietary protein level. Adrenalectomy lowered the level of the amino acid in the hepatoma from rats fed 12 and 60% protein diets, but adrenalectomy had no effect on rats fed a 30% protein diet. A complex relationship was also observed between the dietary protein level and the effect of hydrocortisone and glucagon treatment on the uptake of the amino acid by normal liver.

A diversity was observed in the response of the amino acid transport system of the diploid hepatomas to hydrocortisone and glucagon treatment. Hepatoma 7800 and the host liver both showed an increased uptake in response to hydrocortisone and glucagon. The uptake of the amino acid by Hepatoma 9618A did not respond to hydrocortisone or glucagon but was increased by glucagon administration to hydrocortisone-treated rats. However, Hepatoma 9633 showed no response to the separate or combined treatments with these hormones, although the host liver did respond.

The amino acid-concentrating abilities of these hepatomas and their response to hormonal treatments showed a positive correlation with the activities of serine dehydratase and tyrosine transaminase previously reported for these hepatomas (40). These data in conjunction with the previously reported data suggest a possible relationship between the control of amino acid transport and the adaptive amino acid-metabolizing enzymes in liver and hepatoma tissues.

¹ This study was supported in part by Grant CA-07175 and Training Grant T01-CA-5002 from the National Cancer Institute, USPHS.

² Postdoctoral fellow, USPHS, 1966–1968. Present address: Department of Physiology and Pharmacology, Duke University Medical Center, Durham, N. C. 27703.

³ Present address: Department of Biochemistry, College of Medicine, Howard University, Washington, D. C. 20001. Supported in part by USPHS Grant No. CA-10729.

Received 3/19/69. Accepted 6/12/69.

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