Protein depletion and replenishment in mice: different roles of
muscle and liver..
Scornik, Oscar A., Scott K. Howell, and Violeta Botbol.
Department of Biochemistry, Dartmouth Medical School, 7200 Vail
Building, Room 402, Hanover, NH 03755-3844, Tel (603) 650-1630, Fax
(603) 650-1128, email oscar.scornik@dartmouth.edu
APStracts 4:0189E, 1997.
Fully grown male CD-1 mice, fed a protein-free diet for 3 days,
received 1 g of starch with or without 300 mg casein by intragastric
intubation. We surveyed the acute effects of these nutrients on
protein synthesis in all tissues (by extrapolating to infinity the
incorporation of radioactive leucine after its injection in massive
doses), and protein degradation in skeletal muscle and liver (by the
accumulation of bestatin-induced peptide intermediates). Muscle
proteolysis was the major source of N during depletion. Compared to
postabsorptive animals, starch suppressed muscle protein loss
(synthesis +21%, degradation -24%, p<0.01) and stimulated hepatic
proteolysis (degradation +28%, p<0.01). Addition of casein to the
starch was anabolic in liver (synthesis +41%, degradation -33%,
p<0.01), gastrointestinal tract, pancreas, and skin (synthesis +38,
+69 and +38%, p<0.01), but had no effect on muscle. Protein
turnover proved uniquely sensitive to the dietary supply of
carbohydrates in muscle, and to the endogenous or exogenous supply of
amino acids in liver.
Received 13 February 1997; accepted in final form 15 August 1997.
APS Manuscript Number E70-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 27 August 1997