No abstract

The effects of endurance training on the enzyme activity, protein content, and mRNA abundance of Mn and CuZn superoxide dismutase (SOD) were studied in various phenotypes of rat skeletal muscle. Female Sprague-Dawley rats were randomly divided into trained (T, n = 8) and untrained (U, n = 8) groups. Training, consisting of treadmill running at 27 m/min and 12% grade for 2 h/day, 5 days/wk for 10 wk, significantly increased citrate synthase activity ( P < 0.01) in the type I (soleus), type IIa (deep vastus lateralis, DVL), and mixed type II (plantaris) muscles but not in type IIb (superficial vastus lateralis, SVL) muscle. Mitochondrial (Mn) SOD activity was elevated by 80% ( P < 0.05) with training in DVL. SVL and plantaris muscle in T rats showed 54 and 42% higher pooled immunoreactive Mn SOD protein content, respectively, than those in U rats. However, no change in Mn SOD mRNA level was found in any of the muscles. CuZn SOD activity, protein content, and mRNA level in general were not affected by training, except for a 160% increase in pooled CuZn SOD protein in SVL. Training also significantly increased glutathione peroxidase and catalase activities ( P < 0.05), but only in DVL muscle. These data indicate that training adaptations of Mn SOD and other antioxidant enzymes occur primarily in type IIa fibers, probably as a result of enhanced free radical generation and modest antioxidant capacity. Differential training responses of mRNA, enzyme protein, and activity suggest that separate cellular signals may control pre- and posttranslational regulation of SOD.

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Responses of contractile properties of soleus to unloading and/or changes in high-energy phosphate contents were studied in rats. Reduction of high-energy phosphates, especially phosphocreatine, in ankle extensors was induced by feeding beta-guanidinopropionic acid (beta-GPA). The major finding in the study was that the fatigability and speed-related contractile properties responded to unloading and creatine supplementation in a similar manner. The high-energy phosphate contents tended to be elevated after 10-d supplementation of creatine and hindlimb suspension. The shift toward slow-type, mainly due to an increased one-half relaxation time, was seen in rats fed beta-GPA. Such a shift was reversed by feeding creatine or by hindlimb suspension; however, the suspension-induced shift of contractile properties toward fast-type was not prevented completely by beta-GPA feeding. Although the muscle fatigue resistance did not change by beta-GPA feeding alone, the decrease in fatigue resistance following suspension and creatine supply was less in the beta-GPA group. It is suggested that the levels of high-energy phosphates and tension production play important roles in the regulation of contractile properties of the soleus muscle.

To elucidate mechanisms underlying acute cold stress-induced immunosuppression, functions of murine peritoneal cells of monocyte/ macrophage lineage from acute cold-stressed mice (exposed to 5 degrees C for 24 h) were investigated. Proliferative responses of spleen cells from control mice (reared at 25 degrees C) stimulated with concanavalin A (ConA) were significantly suppressed by adding peritoneal exudate cells from mice immediately after acute cold stress. The proportion of adherent cells was markedly increased in the peritoneal exudate cells from acute cold-stressed mice. These adherent cells from acute cold-stressed mice were shown to be the cells responsible for the suppressor activity for ConA responses of control spleen cells. Nonadherent cells did not suppress the ConA responses. The adherent cells in peritoneal exudate cells from control mice also suppressed the ConA responses, the inhibitory effect being considerably lower than that from acute cold-stressed mice. Addition of a nitric oxide synthase substrate analogue, NG-monomethyl-L-arginine, to the mixed cell cultures of normal spleen cells and adherent cells from acute cold-stressed mice inhibited nitric oxide release and completely abolished the suppressive effect of the adherent cells, suggesting that reactive nitrogen oxide released from the activated macrophages is apparently involved in the downregulation of proliferative responses of T cells. Thus the present findings suggest that acute cold stress induces macrophages with suppressor function and that this may contribute to the immune-suppressive state seen in spleen cells from acute cold-stressed mice.

Holter ECG in addition to ECG on admission is important for detecting persistent AF or PAF in patients with ischemic stroke, especially with cardioembolism as diagnosed by neuroimaging.

Changes of contractile properties of extensor digitorum longus in response to hindlimb suspension and/or altered high-energy phosphate contents were studied in rats. A reduction of high-energy phosphates, especially phosphocreatine, was seen in rats fed creatine analogue beta-guanidinopropionic acid (beta-GPA), but they were elevated after 10-d supplementation of creatine. The one-half relaxation time was increased by feeding beta-GPA, but was normalized by creatine supply. The fatigue resistance of creatine-depleted muscle was significantly improved, but tended to decrease by suspension and creatine supply, although it was still better than that in the control diet group. It is indicated that the contractile properties of muscle are influenced by the high-energy phosphate content. It is also suggested that the endurance capacity may be influenced by the mitochondrial respiratory capacity, but not necessarily by the levels of high-energy phosphates.

1. We investigated the effect of intermittent exposure to hypobaric hypoxia on the ability of neutrophils to generate.O2-. 2. Seven male volunteers were exposed intermittently to hypobaric hypoxia, equivalent to an altitude of 4500 m, for 7 successive days. Peripheral blood samples were collected before and after the 2 h course of hypobaric hypoxia on days 1 and 7 and neutrophils were subjected to a chemiluminescence assay for.O2- production. 3. On day 1, 2 h exposure to hypobaric hypoxia induced granulocytosis (P < 0.01), but the ability of neutrophils to generate.O2- was unchanged. 4. On day 7, such granulocytosis was not observed, suggesting acclimatization to hypobaric hypoxia. 5. The ability of neutrophils to generate.O2- was significantly increased on day 7 (P < 0.01), although there was no definite change in the mRNA expression of NADPH oxidase subunits in the cells. 6. The results suggest that the ability of neutrophils to generate.O2- may be gradually potentiated by intermittent exposure to hypobaric hypoxia, even after the number of neutrophils in peripheral blood stabilizes.