Slow component of VO2 kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity

Examines the relationship between the magnitude of the relative slow component (SC) of pulmonary oxygen uptake VO[sub 2], citrate synthase activity, UCP2 and UCP3 mRNA levels and muscle fiber composition in both endurance-trained and recreationally active subjects. Magnitude of the relative SC of the Tr group; Indicators of aerobic fitness; High negative correlations between the magnitude of the relative SC and citrate synthase activity and VO[sub 2] peak.

5`-aminoimidazole-4-carboxyamide-ribonucleoside- activated glucose transport is not prevented by nitric oxide synthase inhibition in rat isolated skeletal muscle

1. The nucleoside intermediate 5'-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) activates skeletal muscle AMP-activated protein kinase (AMPK) and increases glucose uptake. The AMPK phosphorylates neuronal nitric oxide synthase (nNOS)µ in skeletal muscle fibres. There is evidence that both AMPK and nNOSµ may be involved in the regulation of contraction-stimulated glucose uptake.
2. We examined whether both AICAR- and contraction-stimulated glucose uptake were mediated by NOS in rat skeletal muscle.
3. Rat isolated epitrochlearis muscles were subjected in vitro to electrically stimulated contractions for 10 min and/or incubated in the presence or absence of AICAR (2 mmol/L) or the NOS inhibitor NG-monomethyl-l-arginine (l-NMMA; 100 µmol/L).
4. Muscle contraction significantly (P < 0.05) altered the metabolic profile of the muscle. In contrast, AICAR and l-NMMA had no effect on the metabolic profile of the muscle, except that AICAR increased muscle 5'-aminoimidazole-4-carboxyamide-ribonucleotide (ZMP) and AICAR content. Nitric oxide synthase inhibition caused a small but significant (P < 0.05) reduction in basal 3-O-methylglucose transport, which was observed in all treatments. 5'-Aminoimidazole-4-carboxyamide-ribonucleoside significantly increased (P < 0.05) glucose transport above basal, with NOS inhibition decreasing this slightly (increased by 209% above basal compared with 184% above basal with NOS inhibition). Contraction significantly increased glucose transport above basal, with NOS inhibition substantially reducing this (107% increase vs 31% increase). 5'-Aminoimidazole-4-carboxyamide-ribonucleoside plus contraction in combination were not additive on glucose transport.
5. These results suggest that NO plays a role in basal glucose uptake and may regulate contraction-stimulated glucose uptake. However, NOS/nitric oxide do not appear to be signalling intermediates in AICAR-stimulated skeletal muscle glucose uptake.

Redistribution of glucose from skeletal muscle to adipose tissue during catch-up fat. A link between catch-up growth and later metabolic syndrome.

Catch-up growth, a risk factor for later obesity, type 2 diabetes, and cardiovascular diseases, is characterized by hyperinsulinemia and an accelerated rate for recovering fat mass, i.e., catch-up fat. To identify potential mechanisms in the link between hyperinsulinemia and catch-up fat during catch-up growth, we studied the in vivo action of insulin on glucose utilization in skeletal muscle and adipose tissue in a previously described rat model of weight recovery exhibiting catch-up fat caused by suppressed thermogenesis per se. To do this, we used euglycemic-hyperinsulinemic clamps associated with the labeled 2-deoxy-glucose technique. After 1 week of isocaloric refeeding, when body fat, circulating free fatty acids, or intramyocellular lipids in refed animals had not yet exceeded those of controls, insulin-stimulated glucose utilization in refed animals was lower in skeletal muscles (by 20–43%) but higher in white adipose tissues (by two- to threefold). Furthermore, fatty acid synthase activity was higher in adipose tissues from refed animals than from fed controls. These results suggest that suppressed thermogenesis for the purpose of sparing glucose for catch-up fat, via the coordinated induction of skeletal muscle insulin resistance and adipose tissue insulin hyperresponsiveness, might be a central event in the link between catch-up growth, hyperinsulinemia and risks for later metabolic syndrome.

Vascular distribution of nitric oxide synthase and vasodilation in the Australian lungfish, Neoceratodus forsteri

The presence of nitric oxide synthase (NOS) and role of nitric oxide (NO) in vascular regulation was investigated in the Australian lungfish, Neoceratodus forsteri. No evidence was found for NOS in the endothelium of large and small blood vessels following processing for NADPH-diaphorase histochemistry. However, both NADPH-diaphorase histochemistry and neural NOS immunohistochemistry demonstrated a sparse network of nitrergic nerves in the dorsal aorta, hepatic artery, and branchial arteries, but there were no nitrergic nerves in small blood vessels in tissues. In contrast, nitrergic nerves were found in non-vascular tissues of the lung, gut and kidney. Dual-wire myography was used to determine if NO signalling occurred in the branchial artery of N. forsteri. Both SNP and SIN-1 had no effect on the pre-constricted branchial artery, but the particulate guanylyl cyclase (GC) activator, C-type natriuretic peptide, always caused vasodilation. Nicotine mediated a dilation that was not inhibited by the soluble GC inhibitor, ODQ, or the NOS inhibitor, L-NNA, but was blocked by the cyclooxygenase inhibitor, indomethacin. These data suggest that NO control of the branchial artery is lacking, but that prostaglandins could be endothelial relaxing factors in the vasculature of lungfish.

Local nitric oxide synthase inhibition reduces skeletal muscle glucose uptake but not capillary blood flow during in situ muscle contraction in rats

OBJECTIVE: We have previously shown in humans that local infusion of a nitric oxide synthase (NOS) inhibitor into the femoral artery attenuates the increase in leg glucose uptake during exercise without influencing total leg blood flow. However, rodent studies examining the effect of NOS inhibition on contraction-stimulated skeletal muscle glucose uptake have yielded contradictory results. This study examined the effect of local infusion of an NOS inhibitor on skeletal muscle glucose uptake (2-deoxyglucose) and capillary blood flow (contrast-enhanced ultrasound) during in situ contractions in rats.

RESEARCH DESIGN AND METHODS: Male hooded Wistar rats were anesthetized and one hindleg electrically stimulated to contract (2 Hz, 0.1 ms) for 30 min while the other leg rested. After 10 min, the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (arterial concentration of 5 µmol/l) or saline was infused into the epigastric artery of the contracting leg.

RESULTS: Local NOS inhibition had no effect on blood pressure, heart rate, or muscle contraction force. Contractions increased (P < 0.05) skeletal muscle NOS activity, and this was prevented by L-NAME infusion. NOS inhibition caused a modest significant (P < 0.05) attenuation of the increase in femoral blood flow during contractions, but importantly there was no effect on capillary recruitment. NOS inhibition attenuated (P < 0.05) the increase in contraction-stimulated skeletal muscle glucose uptake by ~35%, without affecting AMP-activated protein kinase (AMPK) activation.

CONCLUSIONS: NOS inhibition attenuated increases in skeletal muscle glucose uptake during contraction without influencing capillary recruitment, suggesting that NO is critical for part of the normal increase in skeletal muscle fiber glucose uptake during contraction.

Effect of nitric oxide synthase inhibition on mitochondrial biogenesis in rat skeletal muscle

The purpose of this study was to determine whether nitric oxide synthase (NOS) inhibition decreased basal and exercise-induced skeletal muscle mitochondrial biogenesis. Male Sprague-Dawley rats were assigned to one of four treatment groups: NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, ingested for 2 days in drinking water, 1 mg/ml) followed by acute exercise, no L-NAME ingestion and acute exercise, rest plus L-NAME, and rest without L-NAME. The exercised rats ran on a treadmill for 53 ± 2 min and were then killed 4 h later. NOS inhibition significantly (P < 0.05; main effect) decreased basal peroxisome proliferator-activated receptor-{gamma} coactivator 1beta (PGC-1beta) mRNA levels and tended (P = 0.08) to decrease mtTFA mRNA levels in the soleus, but not the extensor digitorum longus (EDL) muscle. This coincided with significantly reduced basal levels of cytochrome c oxidase (COX) I and COX IV mRNA, COX IV protein and COX enzyme activity following NOS inhibition in the soleus, but not the EDL muscle. NOS inhibition had no effect on citrate synthase or beta-hydroxyacyl CoA dehydrogenase activity, or cytochrome c protein abundance in the soleus or EDL. NOS inhibition did not reduce the exercise-induced increase in peroxisome proliferator-activated receptor-{gamma} coactivator 1{alpha} (PGC-1{alpha}) mRNA in the soleus or EDL. In conclusion, inhibition of NOS appears to decrease some aspects of the mitochondrial respiratory chain in the soleus under basal conditions, but does not attenuate exercise-induced mitochondrial biogenesis in the soleus or in the EDL.

Identification of a by-product of nitric oxide synthase activity in human acute brain injury with in vivo proton magnetic resonance spectroscopy

BACKGROUND AND PURPOSE: Laboratory studies have been used to identify nitric oxide as a notable mediator in neuronal death after acute brain injury. To our knowledge, this has not previously been confirmed with in vivo study in humans. Our purpose was to seek in vivo evidence for the induction of nitric oxide synthase (NOS) in human acute brain injury by using proton MR spectroscopy.

METHODS: In vitro proton MR spectra were obtained in neural extracts from 30 human cadavers, and in vivo spectra were obtained in 20 patients with acute brain injury and in a similar number of control subjects.

RESULTS: We identified a unique peak at 3.15 ppm by using in vivo proton MR spectroscopy in eight of 20 patients with acute brain injury but not in 20 healthy volunteers (P < .002). On the basis of in vitro data, we have tentatively assigned this peak to citrulline, a NOS by-product.

CONCLUSION: To our knowledge, our findings suggest, for the first time, that excitotoxicity may occur in human acute brain injury. Confirmation with the acquisition of spectra in very early acute cerebral injury would provide a rationale for the use of neuroprotective agents in these conditions, as well as a new noninvasive method for quantification.

PPARγ ligands, 15-deoxy-Δ12,14-prostaglandin J2 and rosiglitazone regulate human cultured airway smooth muscle proliferation through different mechanisms

1. The influence of two peroxisome proliferator-activated receptor γ (PPARγ) ligands, a thiazolidinedione, rosiglitazone (RG) and the prostaglandin D2 metabolite 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) on the proliferation of human cultured airway smooth muscle (HASM) was examined.

2. The increases in HASM cell number in response to basic fibroblast growth factor (bFGF, 300 pm) or thrombin (0.3 U ml−1) were significantly inhibited by either RG (1–10 μm) or 15d-PGJ2 (1–10 μm). The effects of RG, but not 15d-PGJ2, were reversed by the selective PPARγ antagonist GW9662 (1 μm).

3. Neither RG nor 15d-PGJ2 (10 μm) decreased cell viability, or induced apoptosis, suggesting that the regulation of cell number was due to inhibition of proliferation, rather than increased cell death.

4. Flow-cytometric analysis of HASM cell cycle distribution 24 h after bFGF addition showed that RG prevented the progression of cells from G1 to S phase. In contrast, 15d-PGJ2 caused an increase in the proportion of cells in S phase, and a decrease in G2/M, compared to bFGF alone.

5. Neither RG nor 15d-PGJ2 inhibited ERK phosphorylation measured 6 h post mitogen addition. The bFGF-mediated increase in cyclin D1 protein levels after 8 h was reduced in the presence of 15d-PGJ2, but not RG.

6. Although both RG and 15d-PGJ2 can inhibit proliferation of HASM irrespective of the mitogen used, only the antiproliferative effects of RG appear to be PPARγ-dependent. The different antimitogenic mechanisms of 15d-PGJ2 and synthetic ligands for PPARγ may be exploited to optimise the potential for these compounds to inhibit airway remodelling in asthma.

Regulation of glycogen synthase and phosphorylase during recovery from high-intensity exercise in the rat

The aim of this study was to determine the role of the phosphorylation state of glycogen synthase and glycogen phosphorylase in the regulation of muscle glycogen repletion in fasted animals recovering from high-intensity exercise. Groups of rats were swum to exhaustion and allowed to recover for up to 120 min without access to food. Swimming to exhaustion caused substantial glycogen breakdown and lactate accumulation in the red, white and mixed gastrocnemius muscles, whereas the glycogen content in the soleus muscle remained stable. During the first 40 min of recovery, significant repletion of glycogen occurred in all muscles examined except the soleus muscle. At the onset of recovery, the activity ratios and fractional velocities of glycogen synthase in the red, white and mixed gastrocnemius muscles were higher than basal, but returned to pre-exercise levels within 20 min after exercise. In contrast, after exercise the activity ratios of glycogen phosphorylase in the same muscles were lower than basal, and increased to pre-exercise levels within 20 min. This pattern of changes in glycogen synthase and phosphorylase activities, never reported before, suggests that the integrated regulation of the phosphorylation state of both glycogen synthase and phosphorylase might be involved in the control of glycogen deposition after high-intensity exercise.