Sites of protein conservation and loss during starvation: influence of adiposity.

Previous studies have established that older (16 wk) and more obese rats conserve body protein during prolonged starvation. This adaptation is due in part to a curtailment of muscle proteolysis. To determine whether this response occurs also in younger rats and whether protein is conserved at sites other than muscle, studies were conducted in young 6-wk-old rats previously fed either a chow or a high-fat diet before starvation.

Glucose uptake and insulin sensitivity in rat muscle: changes during 3-96 weeks of age.

It has been demonstrated that aging diminishes the rate of glucose utilization by rat skeletal muscle. To determine the basis for this occurrence as well as its temporal sequence, glucose utilization was examined in isolated hindquarters of 3-, 5-, 8-, 16-, 24-, 48-, and 96-wk-old male Sprague-Dawley rats. Glucose utilization diminished progressively during early development (3-5 wk) and adolescence (5-16 wk) in hindquarters perfused in the absence of added insulin.

Catecholamine-thyroid hormone interaction on myocardial ornithine decarboxylase.

Myocardial phosphorylase alpha activity responds to stimulation by catecholamines and thyroid hormone. In hyperthyroidism this enzyme is supersensitive to beta-adrenergic stimulation and blockade, indicating that its increased activity is an indirect effect of thyroid hormone. Myocardial ornithine decarboxylase (ODC) activity also responds to catecholamine and thyroid hormone stimulation.

Muscle glycogenolysis during exercise: dual control by epinephrine and contractions.

The interaction of epinephrine and contractions on muscle metabolism was studied in the isolated perfused rat hindquarter. Subtetanic contractions (180/min) through 20 min elicited glycogenolysis and increased phosphorylase a activity. In the soleus, a slow-twitch red muscle, these effects were transient, but when epinephrine at a physiological concentration (2.

Thyroid-hormone effects on ornithine decarboxylase.

We examined thyroidectomized, normal and hyperthyroid rats and found that ornithine decarboxylase activity was directly correlated with thyroid functional state in heart and liver and unaffected in brain, testes and spleen, phenomena that correlate with the known effect of thyroid hormone on protein synthesis.