Role of factors derived from activated macrophages in regulation of muscle protein turnover.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
V E Baracos
Publications and source records attributed to V E Baracos.
Effect of bovine somatotropin on the distribution of immunoreactive insulin-like growth factor-I in lactating bovine mammary tissue.
The distribution pattern of immunoreactive insulin-like growth factor-I in normal lactating bovine mammary tissue and in tissue obtained after bovine somatotropin treatment was determined by indirect immunofluorescence. In normal tissue, insulin-like growth factor-I immunoreactivity was observed almost exclusively associated with stromal elements. Intralobular stromal cells, small blood vessels, and capillaries all expressed moderate to high immunoreactivity. In contrast, mammary epithelial cells displayed only sparse cytoplasmic immunoreactivity. Immunoreactive material was also present in the periductular connective tissue area, possibly associated with the basal plasma membrane of epithelial cells. Somatotropin treatment of animals resulted in elevated serum insulin-like growth factor-I concentrations and altered the distribution of insulin-like growth factor-I-stainable material in mammary tissue. After somatotropin treatment, immunoreactivity was still detected in mammary stroma; however, prominent staining was also observed in the cytoplasm of mammary epithelial cells. Given the possible role of insulin-like growth factor-I in the regulation of bovine mammary epithelial cell growth and function, our findings raise the possibility that somatotropin may induce insulin-like growth factor-I production in mammary tissue, or other tissues, to influence indirectly the growth or function of the epithelial cells. This offers a possible mechanism for bovine somatotropin stimulation of lactation.
Animals↗
The metabolic cost of fever.
Indirect calorimetry has been employed to demonstrate that fever and infection result in increased metabolic heat production. This response contributes, with reduced dietary energy intake, to negative energy balance in the infected host and constitutes a metabolic "cost". Clinical and experimental studies concerning quantitative aspects of metabolic heat production during fever are summarized. The possible adaptive value of increased heat production in the context of host defence reactions is discussed. The magnitude of increased heat production varies with the severity and duration of the insult, the nutritional and metabolic status of the host, treatment with various drugs, and the ambient temperature at which the measurements are made. More information about these factors is required to assess the metabolic and nutritional needs of individual patients during a febrile illness and subsequent recovery.
Animals↗
Maintenance of normal length improves protein balance and energy status in isolated rat skeletal muscles.
To clarify how muscle length or tension influences protein balance, we examined rates of protein synthesis and degradation in rat muscles incubated at different lengths. In soleus and extensor digitorum longus, protein degradation was lowest at resting length in situ (Lo), where the muscles are under slight tension. Muscles that were unrestrained shortened spontaneously and showed 25-45% greater net protein breakdown than muscles fixed at Lo. Protein synthesis did not differ in the two groups initially, but by 4 or 6 h was 25% greater in muscles at Lo. Maintenance of Lo improved overall protein balance largely through the reduction in proteolysis. In addition, muscles at Lo maintained high levels of ATP and phosphocreatine for 6 h, whereas the unrestrained muscles lost about half their energy stores. The acceleration of proteolysis in the shortened muscle appears independent of prostaglandin E2. However, the acceleration of protein breakdown in the unrestrained muscles could be prevented with inhibitors of thiol proteases (e.g., Ep-475 or leupeptin) or by incubation in Ca2+-free medium or with dantrolene (an inhibitor of Ca2+ release from sarcoplasmic reticulum). These treatments did not reduce the low level of proteolysis in muscles at Lo. Thus, if muscles are allowed to shorten in vitro, proteolysis is activated by a Ca2+-dependent mechanism, involving thiol proteases.
Adenosine Triphosphate↗
Ca2+, interleukin-1 and failure to maintain normal length stimulate protein degradation in isolated skeletal muscle.
Explore the source record for details and available documents.
Animals↗
Effects of temperature on protein turnover in isolated rat skeletal muscle.
To understand the net loss of muscle protein during fever and the possible changes in body protein balance with hyperthermia, we investigated the influence of temperature on protein synthesis and degradation in rat skeletal muscles. In the incubated soleus, extensor digitorum longus, or diaphragm, net protein degradation increased by about 11%/degrees C between 33 and 42 degrees C. This loss of muscle protein resulted from an increase in protein degradation (172% between 33 and 42 degrees C). By contrast, protein synthesis increased by only 25% between 33 and 39 degrees C and fell markedly by 42 degrees C. Unlike muscle, in isolated rat hepatocytes, protein breakdown did not increase significantly between 36 and 39 degrees C. The stimulation of protein degradation between 36 and 39 degrees C was not reduced by leupeptin or Ep-475, which inhibit lysosomal thiol proteases and reduce net protein degradation in the incubated muscles. Prostaglandin E2 (PGE2) has been implicated in the accelerated muscle proteolysis during fever. However, PGE2 release by muscles was unchanged between 33 and 42 degrees C, and inhibition of PGE2 synthesis by indomethacin did not reduce the stimulation of proteolysis at 40 degrees C. This catabolic effect of increased temperature may contribute to the negative nitrogen balance during fever.
Adenosine Triphosphate↗