Biochemical consequences of protein depletion in the rabbit heart

We showed previously that cardiac function was depressed in rabbits subjected to 6 weeks of protein depletion and was restored after 4 weeks of protein refeeding. To identify nutritional or metabolic factors that underlie cardiac dysfunction, we assessed the nutritional status and myocardial content of energy-providing substrates in three groups of rabbits: group I served as control; group II was fed a protein-free diet; and group III was fed a protein-free diet and then repleted. Animal weights were 2.73 +/- 0.22 kg in group I, 1.92 +/- 0.28 kg in group II, and 2.78 +/- 0.12 kg in group III. Serum albumin concentrations decreased from 3.70 +/- 0.12 g/dl in group I to 2.81 +/- 0.10 g/dl in group II, and returned to normal (3.71 +/- 0.11 g/dl) in group III. The heart weights; myocardial contents of water, nitrogen (N), total fat, and glycogen; skeletal muscle N concentrations; and liver N contents were measured. Protein depletion produced a reduction in total cardiac mass due to decreased nitrogen and glycogen contents, but there was an increased fat content. Comparison with other organs suggests that cardiac muscle plays a role in energy homeostasis, undergoing glycogenolysis and proteolysis similar to those of liver and skeletal muscle. Protein repletion restored normal mass of the heart, but not of the liver. We conclude that adequate nutrition may be important in maintaining cardiac function.