Irisin relaxes rat thoracic aorta through inhibiting signaling pathways implicating protein kinase C.

BACKGROUND: Irisin, a newly identified exercise-derived myokine, has been found involved in a peripheral vasodilator effect. However, little is known regarding the potential vascular activity of irisin, and the mechanisms underlying its effects on vascular smooth muscle have not been fully elucidated. This study was aimed to investigate the effects of irisin on vascular smooth muscle contractility in rat thoracic aorta, and the hypothesis that protein kinase C (PKC) may have a role in these effects. METHODS: Isometric contraction-relaxation responses of thoracic aorta rings were measured with an isolated organ bath model. The steady contraction was induced with 10 µM phenylephrine (PHE), and then the concentration-dependent responses of irisin (0.001-1 µM) were examined. The time-matched vehicle control (double distilled water) group was also formed. To evaluate the role of PKC, endothelium-intact thoracic aorta rings were incubated with 150 nM bisindolylmaleimide I (BIM I) for 20 min before the addition of 10 µM PHE and irisin. Also, a vehicle control group was formed for dimethyl sulfoxide (DMSO). RESULTS: Irisin exerted the vasorelaxant effects at concentrations of 0.01, 0.1, and 1 µM compared to the control group (p < 0.001). Besides, PKC inhibitor BIM I incubation significantly inhibited the relaxation responses induced by varying concentrations of irisin (p: 0.000 for 0.01 µM; p: 0.000 for 0.1 µM; p: 0.000 for 1 µM). However, DMSO, a solvent of BIM I, did not modulate the relaxant effects of irisin (p > 0.05). DISCUSSION: In conclusion, physiological findings were obtained regarding the functional relaxing effects of irisin in rat thoracic aorta. The findings demonstrated that irisin induces relaxation responses in endothelium-intact thoracic aorta rings in a concentration-dependent manner. Furthermore, this study is the first to report that irisin-induced relaxation responses are regulated probably via activating signaling pathways implicating PKC.

Irisin Relaxes Rat Trachea via KV Channels, KATP Channels, and BKCa Channels.

BACKGROUND: This study aimed to investigate the effects of irisin on rat tracheal smooth muscle contraction-relaxation responses and the roles of voltage-gated potassium (KV) channels, ATP-sensitive potassium (KATP) channels, and large-conductance calcium-activated potassium (BKCa) channels in these effects. METHODS: Isometric contraction and relaxation responses of tracheal segments were measured using the tissue bath method. Submaximal contractions were induced by ACh (10-5 M) or KCl (60 mM), and then concentration-response curves of irisin (10-9 to 10-6 M) were obtained. For the temporal control, a double-distilled water group was formed. ACh and irisin were added to the baths after tracheal segments were incubated with 4-AP (KV channel blocker), glibenclamide (KATP channel blocker), TEA, and iberiotoxin (BKCa channel blockers) to assess the role of K+ channels. In addition, a vehicle group was performed for the solvent dimethyl sulfoxide (DMSO). RESULTS: Irisin exhibited the relaxant effects in tracheal segments precontracted with both ACh and KCl at concentrations of 10-8-10-6 M (p<0.05). Besides, incubations of 4-AP, glibenclamide, TEA, and iberiotoxin significantly inhibited the irisin-mediated relaxation (p<0.05), whereas DMSO incubation did not modulate irisin responses (p>0.05). CONCLUSION: In conclusion, the first physiological results on the relaxant effects of irisin in rat trachea were obtained. Our findings demonstrated that irisin mediates concentration-dependent relaxation in rat tracheas. Moreover, the present study reported for the first time that irisin-induced bronchorelaxation is associated with the activity of the K+ channels.

Potassium Channels Contributes to Apelin-induced Vasodilation in Rat Thoracic Aorta.

BACKGROUND: Apelin is a newly discovered peptide hormone and originally discovered endogenous apelin receptor ligand. OBJECTIVE: In this study, we aimed to investigate the possible roles of potassium channel subtypes in the vasorelaxant effect mechanisms of apelin. METHODS: The vascular rings obtained from the thoracic aortas of the male Wistar Albino rats were placed into the isolated tissue bath system. The resting tension was set to 2 g. After the equilibration period, the aortic rings were precontracted with 10-5 M phenylephrine (PHE) or 45 mM KCl. Pyroglutamyl-apelin-13 ([Pyr1]apelin-13), which is the dominant apelin isoform in the human cardiovascular tissues and human plasma, was applied cumulatively (10-10-10-6 M) to the aortic rings in the plateau phase. The experimental protocol was repeated in the presence of specific K+ channel subtype blockers to determine the role of K+ channels in the vasorelaxant effect mechanisms of apelin. RESULTS: [Pyr1]apelin-13 induced a concentration-dependent vasorelaxation (p < 0.001). The maximum relaxation level was approximately 52%, according to PHE-induced contraction. Tetraethylammonium, iberiotoxin, 4-Aminopyridine, glyburide, anandamide, and BaCl2 statistically significantly decreased the vasorelaxant effect level of [Pyr1]apelin-13 (p < 0.001). However, apamin didn't statistically significantly change the vasorelaxant effect level of [Pyr1]apelin-13. CONCLUSION: In conclusion, our findings suggest that BKCa, IKCa, Kv, KATP, Kir, and K2P channels are involved in the vasorelaxant effect mechanisms of apelin in the rat thoracic aorta.

Vascular Functional Effect Mechanisms of Elabela in Rat Thoracic Aorta.

BACKGROUND: Elabela is a recently discovered peptide hormone. The present study aims to investigate the vasorelaxant effect mechanisms of elabela in the rat thoracic aorta. METHODS: The vascular rings obtained from the thoracic aortas of the male Wistar albino rats were placed in the isolated tissue bath system. Resting tension was set to 1 gram. After the equilibration period, the vessel rings were contracted with phenylephrine or potassium chloride. Once a stable contraction was achieved, elabela-32 was applied cumulatively (10-9-10-6 molar) to the vascular rings. The experimental protocol was repeated in the presence of specific signaling pathway inhibitors or potassium channel blockers to determine the effect mechanisms of elabela. RESULTS: Elabela showed a significant vasorelaxant effect in a concentration-dependent manner (P < 0.001). The vasorelaxant effect level of elabela was significantly reduced by the apelin receptor antagonist F13A, cyclooxygenase inhibitor indomethacin, adenosine monophosphate-activated protein kinase inhibitor dorsomorphin, protein kinase C inhibitor bisindolmaleimide, large-conductance calcium-activated potassium channel blocker iberiotoxin, and intermediate-conductance calcium-activated potassium channel blocker TRAM-34 (P < 0.001). However, the vasorelaxant effect level of elabela was not significantly affected by the endothelial nitric oxide synthase inhibitor nitro-L-arginine methyl ester and mitogen-activated protein kinase inhibitor U0126. CONCLUSIONS: Elabela exhibits a prominent vasodilator effect in rat thoracic aorta. Apelin receptor, prostanoids, adenosine monophosphate-activated protein kinase, protein kinase C, and calcium-activated potassium channels are involved in the vasorelaxant effect mechanisms of elabela.

Irisin relaxes rat thoracic aorta: MEK1/2 signaling pathway, KV channels, SKCa channels, and BKCa channels are involved in irisin-induced vasodilation.

This study investigated the effects of irisin on vascular smooth muscle contractility in rat thoracic aorta, and the hypothesis that mitogen-activated protein kinase kinase (MEK1/2) signaling pathway, voltage-gated potassium (KV) channels, small-conductance calcium-activated potassium (SKCa) channels, and large-conductance calcium-activated potassium (BKCa) channels may have roles in these effects. Isometric contraction-relaxation responses of isolated thoracic aorta rings were measured with an organ bath model. The steady contraction was induced with 10-5 M phenylephrine (PHE), and then the concentration-dependent responses of irisin (10-9-10-6 M) were examined in endothelium-intact and -denuded rat thoracic aortas. Also, the effects of irisin incubations on PHE-mediated contraction and acetylcholine (ACh) - mediated relaxation were studied. Irisin exerted the vasorelaxant effects in both endothelium-intact and -denuded aortic rings at concentrations of 10-8, 10-7, and 10-6 M compared with the control groups (p < 0.001). Besides, pre-incubation of aortic rings with irisin (10 nM, 100 nM, or 1 µM for 30 min) augmented ACh-mediated (10-9-10-5) vasodilation in PHE-precontracted thoracic aorta segments but did not modulate PHE-mediated (10-9-10-5) contraction. In addition, MEK1/2 inhibitor U0126, KV channel blocker XE-991, SKCa channel blocker apamin, and BKCa channel blocker tetraethylammonium (TEA) incubations significantly inhibited the irisin-induced relaxation responses. In conclusion, the first physiological findings were obtained regarding the functional relaxing effects of irisin in rat thoracic aorta. The findings demonstrated that irisin induces relaxation responses in endothelium-intact and (or) endothelium-denuded aortic rings in a concentration-dependent manner. Furthermore, this study is the first to report that irisin-induced relaxation responses are related to the activity of the MEK1/2 pathway, KV channels, and calcium-activated K+ (SKCa and BKCa) channels.

Physiological role of K+ channels in irisin-induced vasodilation in rat thoracic aorta.

Irisin, an exercise-induced myokine, has been shown to have a peripheral vasodilator effect. However, little is known about the mechanisms underlying its effects. In this study, it was aimed to investigate the vasoactive effects of irisin on rat thoracic aorta, and the hypothesis that voltage-gated potassium (KV) channels, ATP-sensitive potassium (KATP) channels, small-conductance calcium-activated potassium (SKCa) channels, large-conductance calcium-activated potassium (BKCa) channels, intermediate-conductance calcium-activated potassium (IKCa) channels, inward rectifier potassium (Kir) channels, and two-pore domain potassium (K2P) channels may have roles in these effects. Isometric contraction-relaxation responses of isolated thoracic aorta rings were measured with an organ bath model. The steady contraction was induced with both 10-5 M phenylephrine and 45 mM KCl, and then the concentration-dependent responses of irisin (10-9-10-6 M) were examined. Irisin exerted the vasorelaxant effects in both endothelium-intact and -denuded aortic rings at concentrations of 10-8, 10-7, and 10-6 M (p < 0.001). Besides, KV channel blocker 4-aminopyridine, KATP channel blocker glibenclamide, SKCa channel blocker apamin, BKCa channel blockers tetraethylammonium and iberiotoxin, IKCa channel blocker TRAM-34, and Kir channel blocker barium chloride incubations significantly inhibited the irisin-induced relaxation responses. However, incubation of K2P TASK-1 channel blocker anandamide did not cause a significant decrease in the relaxation responses of irisin. In conclusion, the first physiological findings were obtained regarding the functional relaxing effects of irisin in rat thoracic aorta. Furthermore, this study is the first to report that irisin-induced relaxation responses are associated with the activity of KV, KATP, SKCa, BKCa, IKCa, and Kir channels.

[Pyr1]apelin-13 relaxes the rat thoracic aorta via APJ, NO, AMPK, and potassium channels.

In this study, the effect and effect mechanisms of [Pyr1]apelin-13, the dominant apelin isoform in the human cardiovascular tissues and human plasma, on vascular contractility were investigated. The vascular rings obtained from the thoracic aortas of the male Wistar Albino rats were placed in the isolated tissue bath system. After the equilibration period, [Pyr1]apelin-13 (10-9 to 10-6 M) was applied cumulatively to the aortic rings pre-contracted with phenylephrine in the plateau phase. The protocol was repeated in the presence of specific signaling pathway inhibitors (F13A, L-NAME, dorsomorphin, TEA, U0126, or indomethacin) to determine the effect mechanisms of [Pyr1]apelin-13. [Pyr1]apelin-13 induced a dose-dependent relaxation in the pre-contracted aortic rings. APJ, eNOS, AMPK, and potassium channel inhibition statistically significantly decreased the vasodilator effect of [Pyr1]apelin-13. MAPK and COX inhibition didn't statistically significantly changed the vasodilator effect of [Pyr1]apelin-13. In conclusion, [Pyr1]apelin-13 relaxes the rat thoracic aorta via APJ, NO, AMPK, and potassium channels.

Neuroprotective effects of melatonin administered alone or in combination with topiramate in neonatal hypoxic-ischemic rat model.

PURPOSE: The objective of this study was to compare the effects of two neuroprotective agents; melatonin, a free radical scavenger and topiramate, AMPA/kainate receptor antagonist, administered alone or in combination in neonatal hypoxic-ischemic model. METHODS: After being anesthetized, 7-day-old pups underwent ischemia followed by exposure to hypoxia. The pups were divided into 4 groups in order to receive the vehicle, melatonin, topiramate and combination of topiramate and melatonin. These were administered intraperitoneally for three times; the first before ischemia, the second after hypoxia and the third 24 hours after the second dose. After sacrification, infarct volume and apoptosis were evaluated. RESULTS: Percent infarcted brain volume was significantly reduced in rats which received drugs compared with those which received the vehicle. The number of TUNEL positive cells per unit area in hippocampus and cortex were markedly reduced in drug treated groups compared with control group. No significant differences were found regarding percent infarcted brain volume and number of TUNEL positive cells among drug-treated groups. CONCLUSIONS: Melatonin and topiramate, administered either alone or in combination significantly reduced the percent infarcted brain volume and number of TUNEL positive cells suggesting that these agents may confer benefit in treatment of infants with hypoxic-ischemic encephalopathy.

The contribution of "resting" body muscles to the slow component of pulmonary oxygen uptake during high-intensity cycling.

Oxygen uptake (VO2) kinetics during moderate constant-workrate (WR) exercise (>lactate-threshold (θL)) are well described as exponential. AboveθL, these kinetics are more complex, consequent to the development of a delayed slow component (VO2sc), whose aetiology remains controversial. To assess the extent of the contribution to the VO2sc from arm muscles involved in postural stability during cycling, six healthy subjects completed an incremental cycle-ergometer test to the tolerable limit for estimation of θL and determination of peak VO2. They then completed two constant-WR tests at 90% of θL and two at 80% of ∆ (difference between θL and VO2peak). Gas exchange variables were derived breath-by-breath. Local oxygenation profiles of the vastus lateralis and biceps brachii muscles were assessed by near-infrared spectroscopy, with maximal voluntary contractions (MVC) of the relevant muscles being performed post-exercise to provide a frame of reference for normalising the exercise-related oxygenation responses across subjects. Above supra-θL, VO2 rose in an exponential-like fashion ("phase 2), with a delayed VO2sc subsequently developing. This was accompanied by an increase in [reduced haemoglobin] relative to baseline (∆[Hb]), which attained 79 ± 13 % (mean, SD) of MVC maximum in vastus lateralis at end-exercise and 52 ± 27 % in biceps brachii. Biceps brachii ∆[Hb] was significantly correlated with VO2 throughout the slow phase. In contrast, for sub- L exercise, VO2 rose exponentially to reach a steady state with a more modest increase in vastus lateralis ∆[Hb] (30 ± 11 %); biceps brachii ∆[Hb] was minimally affected (8 ± 2 %). That the intramuscular O2 desaturation profile in biceps brachii was proportional to that for VO2sc during supra-θL cycle ergometry is consistent with additional stabilizing arm work contributing to the VO2sc.

Possible neuroprotective effects of magnesium sulfate and melatonin as both pre- and post-treatment in a neonatal hypoxic-ischemic rat model.

BACKGROUND: Perinatal hypoxia-ischemia is a major cause of mortality and long-term neurological deficits. OBJECTIVES: The objective of this study was to compare the effects of two neuroprotective agents; magnesium sulfate and melatonin, administered alone or in combination, on brain infarct volume and TUNEL positivity in a neonatal hypoxic-ischemic (HI) rat model. METHODS: After being anesthetized, 7-day-old pups (n = 80) underwent ischemia followed by exposure to hypoxia for 2 h. The pups were then divided equally and randomly into 4 groups in order to receive the vehicle (saline, control group), magnesium sulfate, melatonin or a combination of magnesium sulfate and melatonin. Treatments were administered intraperitoneally three times; the first being just before ischemia, the second after hypoxia and the third 24 h after the second dose. The pups were sacrificed on postnatal day 10, their brains harvested and evaluated for infarct volume and neuronal apoptosis. RESULTS: Percent infarcted brain volume was significantly reduced in pups receiving the drugs (either magnesium sulfate, melatonin or their combination) compared with those receiving the vehicle. In addition, TUNEL staining showed markedly reduced numbers of TUNEL-positive cells per unit area in the CA1, CA3 and dentate gyrus regions of the hippocampus and in the cortex. However, no statistically significant differences were found regarding percent infarcted brain volume and number of TUNEL-positive cells among the drug-treated groups. CONCLUSIONS: Magnesium sulfate and melatonin, two agents acting at different stages of HI brain damage, administered either alone or in combination, significantly reduced the percent infarcted brain volume and TUNEL positivity, suggesting that these agents may confer a possible benefit in the treatment of infants with HI encephalopathy.

Oxygen uptake kinetics during incremental- and decremental-ramp cycle ergometry.

The pulmonary oxygen uptake (VO2) response to incremental-ramp cycle ergometry typically demonstrates lagged-linear first-order kinetics with a slope of ~10-11 ml·min(-1)·W(-1), both above and below the lactate threshold (θL), i.e. there is no discernible VO2 slow component (or "excess" VO2) above θL. We were interested in determining whether a reverse ramp profile would yield the same response dynamics. Ten healthy males performed a maximum incremental -ramp (15-30 W·min(-1), depending on fitness). On another day, the work rate (WR) was increased abruptly to the incremental maximum and then decremented at the same rate of 15-30 W.min(-1) (step-decremental ramp). Five subjects also performed a sub-maximal ramp-decremental test from 90% of θL. VO2 was determined breath-by-breath from continuous monitoring of respired volumes (turbine) and gas concentrations (mass spectrometer). The incremental-ramp VO2-WR slope was 10.3 ± 0.7 ml·min(-1)·W(-1), whereas that of the descending limb of the decremental ramp was 14.2 ± 1.1 ml·min(-1)·W(-1) (p < 0.005). The sub-maximal decremental-ramp slope, however, was only 9. 8 ± 0.9 ml·min(-1)·W(-1): not significantly different from that of the incremental-ramp. This suggests that the VO2 response in the supra-θL domain of incremental-ramp exercise manifest not actual, but pseudo, first-order kinetics. Key pointsThe slope of the decremental-ramp response is appreciably greater than that of the incremental.The response dynamics in supra-θL domain of the incremental-ramp appear not to manifest actual first-order kinetics.The mechanisms underlying the different dynamic response behaviour for incremental and decremental ramps are presently unclear.

Effect of time of day on the relationship between lactate and ventilatory thresholds: a brief report.

The purpose of this investigation was to study the effect of time of day on the relationship between lactate (LT) and ventilatory thresholds (VT) of pulmonary oxygen uptake (VO2). Seven moderately active male volunteers (26.3 ± 3.0 years, 1.74 ± 0.08 m, 76 ± 5 kg) performed a maximal incremental test (increases of 30 W every 2 min) on a cycle ergometer on consecutive days at 0900 h, 1400h and 1900 h in a randomized fashion. The anaerobic threshold was determined using both ventilatory gas analysis and blood lactate measures. Each of the following variables was recorded both at VT and the LT; heart rate (HR, beats.min(-1)), minute ventilation (VE, L.min(-1)), respiratory exchange ratio (RER), time to threshold (Time, sec), oxygen uptake (VO2, ml·kg(-1).min(-1)) and VO2 as a percentage of maximal oxygen uptake (%VO2max). The correlations between VT and LT variables analyzed by Pearson product moment correlations for each time of day. ANOVA was used to compare the data obtained at different times of the day. There were no significant differences for the data related to time of day either for ventilatory gas analysis or lactate measurements. The correlation coefficients between VT and LT variables were moderate to high (r=0.56-0.94) for time of day. However, the correlations for HR, VO2, and %VO2max (r=0.81-0.94) were slightly stronger compared with Time, VE and RER (r=0.56-0.88). It was concluded that, the data at VT and LT were not influenced by time of day.