Chronic ouabain treatment increases the contribution of nitric oxide to endothelium-dependent relaxation

The aim of this study was to analyze the contribution of nitric oxide, prostacyclin and endothelium-dependent hyperpolarizing factor to endothelium-dependent vasodilation induced by acetylcholine in rat aorta from control and ouabain-induced hypertensive rats. Preincubation with the nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl esther (L-NAME) inhibited the vasodilator response to acetylcholine in segments from both groups but to a greater extent in segments from ouabain-treated rats. Basal and acetylcholine-induced nitric oxide release were higher in segments from ouabain-treated rats. Preincubation with the prostacyclin synthesis Inhibitor tranylcypromine or with the cyclooxygenase inhibitor indomethacin inhibited the vasodilator response to acetylcholine in aortic segments front both groups. The Ca(2+)-dependent potassium channel blocker charybdotoxin inhibited the vasodilator response to acetylcholine only In segments from control rats. These results indicate that hypertension induced by chronic ouabain treatment is accompanied by increased endothelial nitric oxide participation and impaired endothelium-dependent hyperpolarizing factor contribution In acetylcholine-induced relaxation. These effects might explain the lack of effect of ouabain treatment oil acetylcholine responses in rat aorta.

Chronic low frequency/low volume resistance training reduces pro-inflammatory cytokine protein levels and TLR4 mRNA in rat skeletal muscle

Skeletal muscle is the source of pro- and anti-inflammatory cytokines, and recently, it has been recognized as an important source of interleukin 6 (IL-6), a cytokine that exerts inhibitory effects on several pro-inflammatory cytokines. Although dynamic chronic resistance training has been shown to produce the known ""repeated bout effect"", which abolishes the acute muscle damage, performing of high-intensity resistance training has been regarded highly advisable, at least from the hypertrophy perspective. On the other hand, a more therapeutic, ""non-damaging"" resistance training program, mainly composed of concentric forces, low frequency/low volume of training, and the same exercise, could theoretically benefit the muscle when the main issue is to avoid muscle inflammation (as in the treatment of several ""low-grade"" inflammatory diseases) because the acute effect of each resistance exercise session could be diminished/avoided, at the same time that the muscle is still being overloaded in a concentric manner. However, the benefits of such ""less demanding"" resistance training schedule on the muscle inflammatory profile have never been investigated. Therefore, we assessed the protein expression of IL-6, TNF-alpha, IL-10, IL-10/TNF-alpha ratio, and HSP70 levels and mRNA expression of SCF(beta-TrCP), IL-15, and TLR-4 in the skeletal muscle of rats submitted to resistance training. Briefly, animals were randomly assigned to either a control group (S, n = 8) or a resistance-trained group (T, n = 7). Trained rats were exercised over a duration of 12 weeks (two times per day, two times per week). Detection of IL-6, TNF-alpha, IL-10, and HSP70 protein expression was carried out by western blotting and SCF(beta-TrCP) (SKP Cullin F-Box Protein Ligases), a class of enzymes involved in the ubiquitination of protein substrates to proteasomal degradation, IL-15, and TLR-4 by RT-PCR. Our results show a decreased expression of TNF-alpha and TLR4 mRNA (40 and 60%, respectively; p < 0.05) in the plantar muscle from trained, when compared with control rats. In conclusion, exercise training induced decreased TNF-alpha and TLR-4 expressions, resulting in a modified IL-10/TNF-alpha ratio in the skeletal muscle. These data show that, in healthy rats, 12-week resistance training, predominantly composed of concentric stimuli and low frequency/low volume schedule, down regulates skeletal muscle production of cytokines involved in the onset, maintenance, and regulation of inXammation.

Switching control of sympathetic activity from forebrain to hindbrain in chronic dehydration

We investigated the mechanisms responsible for increased blood pressure and sympathetic nerve activity (SNA) caused by 2-3 days dehydration (DH) both in vivo and in situ preparations. In euhydrated (EH) rats, systemic application of the AT(1) receptor antagonist Losartan and subsequent pre-collicular transection (to remove the hypothalamus) significantly reduced thoracic (t) SNA. In contrast, in DH rats, Losartan, followed by pre-collicular and pontine transections, failed to reduce tSNA, whereas transection at the medulla-spinal cord junction massively reduced tSNA. In DH but not EH rats, selective inhibition of the commissural nucleus tractus solitarii (cNTS) significantly reduced tSNA. Comparable data were obtained in both in situ and in vivo (anaesthetized/conscious) rats and suggest that following chronic dehydration, the control of tSNA transfers from supra-brainstem structures (e. g. hypothalamus) to the medulla oblongata, particularly the cNTS. As microarray analysis revealed up-regulation of AP1 transcription factor JunD in the dehydrated cNTS, we tested the hypothesis that AP1 transcription factor activity is responsible for dehydration-induced functional plasticity. When AP1 activity was blocked in the cNTS using a viral vector expressing a dominant negative FosB, cNTS inactivation was ineffective. However, tSNA was decreased after pre-collicular transection, a response similar to that seen in EHrats. Thus, the dehydration-induced switch in control of tSNA from hypothalamus to cNTS seems to be mediated via activation of AP1 transcription factors in the cNTS. If AP1 activity is blocked in the cNTS during dehydration, sympathetic activity control reverts back to forebrain regions. This unique reciprocating neural structure-switching plasticity between brain centres emphasizes the multiple mechanisms available for the adaptive response to dehydration.