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Effect of Protein Intake on Amino Acid Transport and Adenosine 3',5'-Monophosphate Content in Rat Liver^{1 ,2}

The Departments of Biochemistry and Nutritional Sciences, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706

The effects of protein intake on hepatic amino acid transport and cyclic AMP content have been determined in the rat. Within 1 day after feeding an 80% casein diet ad libitum, net transport of -aminoisobutyric acid in liver slice preparations was doubled; the response decreased thereafter. Feeding one high protein meal to rats trained to eat a normal diet for 3 hours daily doubled and tripled hepatic AIB uptake at 0.5 and 1 hour, respectively; thereafter uptake decreased with time but at 24 hours was still slightly above that in control slices. Cycloleucine transport also increased rapidly and then declined with time in slices from trained rats fed one high protein meal. Adrenalectomized rats fed a high protein diet ad libitum for 1 to 5 days responded as did intact rats. Hepatic adenosine 3',5'-monophosphate concentration increased by factors of 2 and 2.5 within 15 and 30 minutes, respectively, after feeding one high protein meal to rats trained to eat once a day. This increase was maintained for several hours after feeding began but declined therafter. Stimulation of amino acid transport by feeding a high protein meal may be the result of a small, but rapid, increase in hepatic adenosine 3',5'-monophosphate content.

KEY WORDS: • amino acid transport • cyclic AMP • nonmetabolizable amino acids • protein intake

¹ Supported by funds from the College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin, by Public Health Service Grant AM 10747 from the National Institute of Arthritis and Metabolic Diseases and a grant from The Nutrition Foundation, New York.

² Preliminary reports have been presented at annual meetings of the Federation of American Societies for Experimental Biology: 1969 Federation Proc. 28: 301; 1971 Federation Proc. 30: 235.

Manuscript received 20 August 1971.