In the acquired form of myasthenia gravis in dogs, there are circulating antibodies to acetylcholine receptors (AChRs) and a reduction in the number of AChRs in the postsynaptic membrane. In this study, immune complexes were localized at the neuromuscular junctions in biopsy samples from 10 myasthenic dogs by immunocytochemical means employing conjugates of staphylococcal protein A and horseradish peroxidase. Immune complexes were observed in approximately 70% of the neuromuscular junctions studied in both type 1 and type 2 myofibers. Thus, acquired canine myasthenia gravis appears to involve immune-mediated mechanisms that destroy AChRs in a manner similar to myasthenia gravis in humans. Protein A was also observed to bind principally to elastic fibers in small arteries and arterioles of some myasthenic and control dogs; however, the significance of that localization is unknown.

Animals↗

PubMedDate not supplied

Innovations in mission architectures for exploration beyond low Earth orbit.

Through the application of advanced technologies and mission concepts, architectures for missions beyond Earth orbit have been dramatically simplified. These concepts enable a stepping stone approach to science driven; technology enabled human and robotic exploration. Numbers and masses of vehicles required are greatly reduced, yet the pursuit of a broader range of science objectives is enabled. The scope of human missions considered range from the assembly and maintenance of large aperture telescopes for emplacement at the Sun-Earth libration point L2, to human missions to asteroids, the moon and Mars. The vehicle designs are developed for proof of concept, to validate mission approaches and understand the value of new technologies. The stepping stone approach employs an incremental buildup of capabilities, which allows for future decision points on exploration objectives. It enables testing of technologies to achieve greater reliability and understanding of costs for the next steps in exploration.

Astronomy↗

PubMedDate not supplied

Muscle protein metabolism of rats in surgical trauma.

The effects of decreased food intake and degree of surgical trauma on total, myofibrillar and sarcoplasmic muscle protein synthesis and degradation were assessed in two experiments (A and B). Trauma consisted of an abdominal incision with or without hysterectomy. The degree of trauma in experiment B was increased relative to that in experiment A by extending the length of the incision, operative manipulation and time required to perform the surgery. To account for postoperative diminutions in food intake on protein turnover, a group of nonoperated rats were pair-fed to the level of food consumed by hysterectomized rats. Traumatized rats in experiment B lost more weight, ate less, and had a lower muscle total protein concentration than corresponding rats in experiment A, confirming a more severe trauma in experiment B. In both experiments, trauma depressed total protein content of muscle. Synthesis was measured by the incorporation of L-[U-14C] tyrosine from a single meal into total, sarcoplasmic and myofibrillar proteins of gastrocnemius muscle. Degradation was calculated as the difference between the growth rate and the synthetic rate. Synthetic rate (ks) of total protein was depressed by surgical trauma; the more severe the trauma, the greater the depression. In mild trauma, the depression in ks was due only to a decrease in sarcoplasmic protein synthesis (ke), whereas with more severe trauma, synthetic rates of both sarcoplasmic (kes) and myofibrillar (kem) proteins were decreased. Protein degradation (kd,) was increased on day 2 in experiments A and B, had returned to control values on day 4 in experiment A and had decreased below control values in experiment B.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗

PubMedDate not supplied

Postsurgical muscle protein turnover in perfused hindquarters of the rat.

Skeletal muscle protein synthesis and degradation were measured simultaneously in perfused hindquarters of adult female rats 0, 2, and 4 days after surgical trauma. In order to explore the role of decreased postoperative nutrient intake on muscle protein turnover, a group of rats were pair-fed to the level of food consumed by surgical traumatized animals. Protein synthesis was measured by the incorporation of 3H-L-phenylalanine into the myofibrillar (contractile) and sarcoplasmic (soluble) proteins of gastrocnemius muscle. Protein degradation rates were calculated from the release of myofibrillar 3-methyl histidine (3MH) during the perfusion. Surgical trauma significantly depressed myofibrillar and sarcoplasmic protein synthetic rates by 33 and 29%, respectively. Protein degradation, as assessed by 3MH release into perfusate, increased 25% on the second postoperative day but returned to control levels by the 4th day after surgery. Food restriction of the pair-fed control rats did not alter protein synthesis, however, protein degradation decreased significantly. In conclusion, the effect of trauma on protein turnover appears not to be due to decreased nutrient consumption.

Animals↗

PubMedDate not supplied

Comparative effects of thermal and surgical trauma on rat muscle protein metabolism.

A modified intraperitoneal pool flooding technique, employing L-3H-tyrosine, was developed for measuring muscle protein synthetic rates following traumatic injury. Sufficient radiolabeled tyrosine was injected intraperitoneally to effect a six-fold increase in plasma tyrosine concentration (124-800 microM) resulting in constant, sustained specific radioactivities in plasma- and intracellular-free tyrosine pools. Localized vs systemic effects of thermal and surgical trauma on gastrocnemius muscle protein turnover were assessed 2 and 4 days postinjury. Thermal trauma increased total, myofibrillar, and sarcoplasmic muscle protein synthesis (44%) and protein degradation (300%). Conversely, surgical trauma decreased synthesis of total (24%), myofibrillar (14%), and sarcoplasmic (43%) muscle proteins without altering protein degradation. Short-term restriction of pair-fed controls did not affect either aspect of protein turnover.

Animals↗