Muscle Contraction In Rats Research Articles

Does Sertraline Affect Contraction in Endothelium Damaged Aorta

Aim: Selective Serotonin Reuptake Inhibitor (SSRI) group antidepressants are frequently used in heart patients. In the study, we aimed to investigate the effects of sertraline (SE) on aortic contraction on healthy/damaged rat aorta. Materials and Methods: Wistar albino rats (24) were divided into group1-aorta-intact endothelium and group2-aorta-damaged endothelium. The isolated aortic tissues were placed in organ baths. Changes in the isometric tension of the aortic rings were recorded. Contractions were recorded in both groups after the application of phenylephrine (PE 10-6M). Afterwards, cumulative sertraline (SE 50 mg) (10-9-10-4M) was given to group 1. In Group 2, to control aortic endothelial damage, acetylcholine (10-6M) was applied and the tissues were washed for an hour, the second dose of PE was given, then SE was given cumulatively (10-9-10-4M), and contractions were recorded. Results: After cumulative SE (10-9-10-4M) was given to Group 1, a significant inhibition in spontaneous contractions was detected in the first three sertraline doses (10-9,10-8,10-7)(p<0.05), and in the remaining sertraline doses contraction inhibition continued. When comparing SE 10 6,-5,-4 and 10-9,-8,-7 doses, there was inhibition of contractions (p<0.005). In group2, the inhibition of second PE contractions continued after sertraline doses, but the inhibition was observed less than in group1 (p<0.05). Conclusion: SE inhibited PE-induced smooth muscle contraction in rat isolated aorta. PE-induced smooth muscle contractions were inhibited more slowly in the endothelium-damaged aorta. It is thought that NO release and NO-dependent vasodilation in the aorta decrease as a result of damage. A clearer understanding of the effects of sertraline on the cardiovascular system will be possible with further research. Keywords: Aorta, endothelium, sertraline, contraction, vasorelaxation

Exaggerated blood pressure response to static exercise in hindlimb ischemia-reperfusion.

Peripheral artery disease (PAD) reduces the blood flow supply in the affected limbs as one of the significant cardiovascular concerns. Revascularization surgery in the femoral artery plays a central role in treating PAD. Exercise is also a rehabilitation strategy suggested for PAD patients to improve vascular functions. However, the effects of limb ischemia-reperfusion (IR), one of the most predominant complications in revascularization surgery, on exercise-induced arterial blood pressure (BP) response are poorly understood. In the present study, we determined 1) the blood flow status in the hindlimb muscles of rats (plantar muscle, red and white portions of gastrocnemius) with different time points of the hindlimb IR; and 2) the BP response to static muscle contraction in rats at different time points after the blood flow reperfusion procedure. Results of this study indicated that, compared with the Sham group, the blood flow in the hindlimb muscles evaluated by Evans blue concentration was significantly reduced at 6h of femoral artery occlusion (FAO 6h) (vs. sham control, p < 0.05). The decreased blood flow was gradually recovered after the blood flow reperfusion for 18 (IR 18h), 66 (IR 66h), and 114 (IR 114h) hours (p < 0.05 vs. FAO 6h for all IR groups). The response of mean arterial pressure was 20 ± 4mmHg in Sham rats (n = 7); 32 ± 10mmHg in IR 18h rats (n = 10); 27 ± 7mmHg in IR 66h rats (n = 13); 26 ± 4mmHg in IR 114h rats (n = 9) (p < 0.05 vs. Sham for all groups). No significant difference was observed in the peak-developed tension during muscle contraction among all the groups (p > 0.05). In conclusion, static exercise-induced BP response is exaggerated following IR. Whereas the BP response is not statistically significant but tends to decrease with a prolonged IR time, the exaggerated BP response remains through time points from post-IR 18h-114h.

C60 fullerene attenuates muscle force reduction in a rat during fatigue development

C60 fullerene (C60) as a nanocarbon particle, compatible with biological structures, capable of penetrating through cell membranes and effectively scavenging free radicals, is widely used in biomedicine. A protective effect of C60 on the biomechanics of fast (m. gastrocnemius) and slow (m. soleus) muscle contraction in rats and the pro- and antioxidant balance of muscle tissue during the development of muscle fatigue was studied compared to the same effect of the known antioxidant N-acetylcysteine (NAC). C60 and NAC were administered intraperitoneally at doses of 1 and 150 mg kg−1, respectively, daily for 5 days and 1 h before the start of the experiment. The following quantitative markers of muscle fatigue were used: the force of muscle contraction, the level of accumulation of secondary products of lipid peroxidation (TBARS) and the oxygen metabolite H2O2, the activity of first-line antioxidant defense enzymes (superoxide dismutase (SOD) and catalase (CAT)), and the condition of the glutathione system (reduced glutathione (GSH) content and the activity of the glutathione peroxidase (GPx) enzyme). The analysis of the muscle contraction force dynamics in rats against the background of induced muscle fatigue showed, that the effect of C60, 1 h after drug administration, was (15–17)% more effective on fast muscles than on slow muscles. A further slight increase in the effect of C60 was revealed after 2 h of drug injection, (7–9)% in the case of m. gastrocnemius and (5–6)% in the case of m. soleus. An increase in the effect of using C60 occurred within 4 days (the difference between 4 and 5 days did not exceed (3–5)%) and exceeded the effect of NAC by (32–34)%. The analysis of biochemical parameters in rat muscle tissues showed that long-term application of C60 contributed to their decrease by (10–30)% and (5–20)% in fast and slow muscles, respectively, on the 5th day of the experiment. At the same time, the protective effect of C60 was higher compared to NAC by (28–44)%. The obtained results indicate the prospect of using C60 as a potential protective nano agent to improve the efficiency of skeletal muscle function by modifying the reactive oxygen species-dependent mechanisms that play an important role in the processes of muscle fatigue development.

Botulinum Toxin A, a Better Choice for Skeletal Muscle Block in a Comparative Study With Lidocaine in Rats.

A positive response to scalene muscle block (SMB) is an important indication for the diagnosis of thoracic outlet syndrome. Lidocaine injection is commonly used in clinical practice in SMB, although there have been some cases of misdiagnosis. Botulinum toxin A (BTX-A) is one of the therapeutic agents in SMB, but whether it is also indicated for SMB diagnosis is controversial. To evaluate the muscle block efficiency of these two drugs, the contraction strength was repeatedly recorded on tibialis anterior muscle in rats. It was found that at a safe dosage, 2% lidocaine performed best at 40 μL, but it still exhibits an unsatisfactory partial blocking efficiency. Moreover, neither lidocaine injection in combination with epinephrine or dexamethasone nor multiple locations injection could improve the blocking efficiency. On the other hand, injections of 3, 6, and 12 U/kg BTX-A all showed almost complete muscle block. Gait analysis showed that antagonistic gastrocnemius muscle, responsible for heel rising, was paralyzed for nonspecific blockage in the 12 U/kg BTX-A group, but not in the 3 U/kg or 6 U/kg BTX-A group. Cleaved synaptosomal associated protein 25 (c-SNAP 25) was stained to test the transportation of BTX-A, and was additionally observed in the peripheral muscles in 6 and 12 U/kg groups. c-SNAP 25, however, was barely detectable in the spinal cord after BTX-A administration. Therefore, our results suggest that low dosage of BTX-A may be a promising option for the diagnostic SMB of thoracic outlet syndrome. SIGNIFICANCE STATEMENT: Muscle block is important for the diagnosis and treatment of thoracic outlet syndrome and commonly performed with lidocaine. However, misdiagnosis was observed sometimes. Here, we found that intramuscular injection of optimal dosage lidocaine only partially blocked the muscle contraction in rats, whereas low-dosage botulinum toxin, barely used in diagnostic block, showed almost complete block without affecting the central nervous system. This study suggests that botulinum toxin might be more suitable for muscle block than lidocaine in clinical practice.

Abstract 10234: Exaggerated Blood Pressure Response to Static Exercise Following Muscle Ischemia-Reperfusion: A Time-Course Investigation

Background: Peripheral artery disease (PAD) is one of the major cardiovascular concerns and dramatically reduces the blood flow supply in the affected limbs. A combination of revascularization surgery in the femoral artery and supervised exercise intervention is among the most general approaches for the treatment of PAD. However, the effects of ischemia-reperfusion (IR), which is one of the most predominant complications resulting from the revascularization surgery, on exercise-induced arterial blood pressure (BP) response are poorly understood. Methods: We examined the BP response to static muscle contraction in rats at different time points after the IR procedure. Four groups were included: 1. Sham rats; 2. Rats with 18 hours following IR (IR 18h); 3. Rats with 66 hours following IR (IR 66h); 4. Rats with 114 hours following IR (IR 114h). One-way ANOVA with LSD post-hoc test was applied to analyze the difference among groups. Data were presented as Mean ± Standard Deviation. Results: Compared with Sham group, the BP response to static muscle contraction was significantly increased in rats with all the investigated time points. The response of mean arterial pressure was 19±3 mmHg in Sham rats (n=6); 29±9 mmHg in IR 18h rats (n=8); 26±7 mmHg in IR 66h rats (n=10); 26±4 mmHg in IR 114h rats (n=9) ( P &lt;0.05; the groups at three time courses vs. Sham). There was no significant difference observed in the peak developed tension during muscle contraction among all the groups (Sham rats: 543±101g; IR 18h rats: 520±28g; IR 66h rats: 554±66g; IR 114h rats: 562±45g; P &gt;0.05). Conclusions: IR significantly exaggerates the static exercise-induced BP response. Whereas the BP response tends to decrease with the prolonged IR time, the exaggerated BP response remains through time points from post IR 18 hours to 114 hours. The data suggest that a chronic time course should be considered to alleviate IR-induced ischemic injury in PAD patients for clinical interventions appropriated and exercise.

Effects of dihydropyridine receptor signal on sarcoplasmic reticulum Ca2+ leakage after muscle contractions in rats

The purpose of this study is to investigate the mechanism underlying sarcoplasmic reticulum (SR) Ca2+ leakage at recovery phase after in vivo contractions. Rat gastrocnemius muscles were electrically stimulated in vivo, and then mechanically skinned fibers were prepared from the muscles excised 30 min after repeated high-intensity contractions. SR Ca2+ leakage was increased in the skinned fibers from stimulated muscles. Thereafter, SR Ca2+ leakage in skinned fibers was measured (1) under a continuously depolarized condition and (2) in the presence of nifedipine in the sealed transverse tubular system. In either of the two conditions, SR Ca2+ leakage in the rested fibers reached a level similar to that in the stimulated fibers. Furthermore, 1 mM tetracaine (Tet) treatment, but not 3 mM Mg2+ (3 Mg) treatment, lessened SR Ca2+ leakage in stimulated fibers. Depolarization-induced force in skinned fibers was more greatly decreased by Tet treatment than by 3 Mg treatment (92% reduction in Tet versus 31% reduction in 3 Mg), whereas caffeine-induced force in skinned fibers was similarly decreased by either treatment (73% reduction in Tet versus 75% reduction in 3 Mg). This difference indicates that Tet exerts a greater inhibitory effect on the dihydropyridine receptor (DHPR) signal to ryanodine receptor (RYR) than 3 Mg, although their inhibitory effects on RYR are almost similar. These results suggest that the increased Ca2+ leakage after muscle contractions is mainly caused by the orthograde signal of DHPRs to RYRs.

Deletion of BK channels decreased skeletal and cardiac muscle function but increased smooth muscle contraction in rats

Large conductance calcium-activated potassium channel (BK channel) is widely expressed in skeletal muscle, myocardium, smooth muscle and other muscle tissues. Mutation, abnormal expression and altered activity of BK channel are linked to muscle-related diseases such as dyskinesia, epilepsy and erectile dysfunction. In order to compare the effects of BK channel on different muscle tissues, we constructed BK channel gene knockout rats‌‌‌‌‍‍‍ (BK-/- rats). HE staining, open field and grip strength tests, ultrasound, blood pressure measurement and vascular tension test were utilized to explore the effects of BK channel deletion on the structure and function changes in skeletal muscle, myocardium, and vascular smooth muscle (VSM). It was found that compared with wild-type rats, the BK-/- rats showed decreased skeletal muscle fiber area, grip, movement distance and speed at 2 and 12 months of ages. At heart, the muscle fiber area, cardiac systolic/diastolic function and heart rate decreased in BK-/- rats. The wall of the left ventricle became thin. However, the vascular wall of BK-/- rats thickened, the pulse wave velocity was increased, and the VSM contraction was enhanced. Unexpectedly, both systolic and diastolic blood pressure were reduced in BK-/- rats, while pulse pressure difference was increased. These results suggest that BK channel may have different effects on different types of muscle tissue, and it should be noted that different parts of muscle tissue may have different effects when BK channel-related drugs are used.

Effects of High Salt Intake on Detrusor Muscle Contraction in Dahl Salt-Sensitive Rats.

High salt intake has been reported as a risk factor for urinary storage symptoms. However, the association between high salt intake and detrusor muscle contraction is not clear. Therefore, we investigated the effects of high salt intake on the components of detrusor muscle contraction in rats. Six-week-old male Dahl salt-resistant (DR; n = 5) and Dahl salt-sensitive (DS; n = 5) rats were fed a high salt (8% NaCl) diet for one week. The contractile responses of the detrusor muscle to the cumulative administration of carbachol and electrical field stimulation (EFS) with and without suramin and atropine were evaluated via isometric tension study. The concentration–response curves of carbachol were shifted more to the left in the DS group than those in the DR group. Contractile responses to EFS were more enhanced in the DS group than those in the DR group (p < 0.05). Cholinergic component-induced responses were more enhanced in the DS group than those in the DR group (p < 0.05). High salt intake might cause urinary storage symptoms via abnormalities in detrusor muscle contraction and the enhancement of cholinergic signals. Excessive salt intake should be avoided to preserve bladder function.

HIF-1α inhibition alleviates the exaggerated exercise pressor reflex in rats with peripheral artery disease induced by femoral artery occlusion.

Hypoxia‐inducible factor 1α (HIF‐1α) is a transcription factor mediating adaptive responses to hypoxia and ischemia. Our previous work showed that HIF‐1α is increased in muscle sensory nerves of rats with peripheral artery disease (PAD) induced by femoral artery occlusion. The present study was further to examine the role played by HIF‐1α in regulating the response of arterial blood pressure (BP) to the activation of muscle afferent nerve during static muscle contraction in rats with femoral artery occlusion. A rat model of femoral artery ligation was used to study PAD in this study. Western blot analysis was employed to examine the protein levels of HIF‐1α in the dorsal root ganglion (DRG) tissues. BAY87, a synthesized compound with the characteristics of highly potent and specific suppressive effects on expression and activity of HIF‐1α, was given into the arterial blood supply of the ischemic hindlimb muscles before the exercise pressor reflex was evoked by static muscle contraction. First, HIF‐1α was increased in the DRG of occluded limbs (optical density: 0.89 ± 0.13 in control versus 1.5 ± 0.05 in occlusion; p < 0.05, n = 6 in each group). Arterial injection of BAY87 (0.2 mg/kg) then inhibited expression of HIF‐1α in the DRG of occluded limbs 3 hr following its injection (optical density: 1.02 ± 0.09 in occluded limbs with BAY87 versus 1.06 ± 0.1 in control limbs; p > 0.05, n = 5 in each group). In addition, muscle contraction evoked a greater increase in BP in occluded rats. BAY87 attenuated the enhanced BP response in occluded rats to a greater degree than in control rats. Our data suggest that the inhibition of HIF‐1α alleviates the exaggeration of the exercise pressor reflex in rats under ischemic circumstances of the hindlimbs in PAD induced by femoral artery occlusion.

The effect of swimming training on adrenomedullin levels, oxidative stress variables, and gastrocnemius muscle contractile properties in hypertensive rats

ABSTRACT Introduction/Aim: Regular exercise may have beneficial effects on high blood-pressure, as shown in different types of experimental hypertension models in rats. The present study aims to investigate the effects of 6-week swimming training on blood pressure, oxidative stress variables of selected tissues, serum adrenomedullin (ADM) levels, and in situ muscle contraction in rats with hypertension induced by Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), an inhibitor of endothelial nitric oxide synthases (eNOs). Materials and Methods: Twenty-six male Sprague Dawley, 8 weeks of age, rats were randomly divided into four groups: (I) normotensive (C), (II) normotensive + exercise (E), (III) hypertensive (L), and (IV) hypertensive + exercise (LE). Hypertension was induced by the oral administration of L-NAME (60 mg/kg) for 6 weeks. Exercise was performed 5 times (1-h each) per week for 6 weeks. At the end of the experiment, blood and tissue samples (the gastrocnemius muscle, heart, kidney, and thoracic aorta) were collected following contractile properties of the gastrocnemius muscle in situ weredetermined. In the collected tissues, oxidative stress (e.g., lipid oxidation and antioxidant enzyme activity) and serum ADM levels were measured. 6-week L-NAME administration per se (Group L) led to a significant increase in systolic and diastolic blood pressure compared to other groups. Results: Importantly, 6-week exercise caused a protective effect of high blood pressure in the rats received L-NAME (Group LE). The level of ADM was lower in the rats received L-NAME than that of the control group. L-NAME increased lipid peroxidation in the thoracic aorta and decreased superoxide dismutase in the heart, kidney and muscle, and decreased catalase and glutathione in the heart. However, the exercise intervention did not have protective effect on the L-NAME-mediated oxidative damage in the collected tissues. Conclusion: In conclusion, 6-week exercise intervention rescued rats from high blood pressure, but did not have ameliorative effect on the decreased ADM levels.

Fiber‐Type Effects of KATP Channel Inhibition via Glibenclamide on the Recovery of Interstitial PO2 Following Muscle Contractions in Rats

KATP channels allow influx of potassium (K+) which hyperpolarizes cell membranes. Glibenclamide (GLI) is a second‐order sulphonylurea often prescribed to Type II diabetic patients to increase insulin release via the inhibition of pancreatic KATP channels. Unfortunately, in vivo studies demonstrate that GLI impairs vasodilation and O2 delivery‐utilization matching (assessed via interstitial PO2, PO2is) in contracting skeletal muscle. Determination of GLI’s impact on PO2is kinetics (T63; time taken to reach 63% of the final response) across muscles comprised of different fiber types during post‐exercise recovery may provide novel insights into mechanisms of fatigue in patients prescribed this medication, particularly in repeated bouts of activity.PurposeTo test the hypothesis that KATP channel inhibition via GLI will slow PO2is kinetics, thus lengthening recovery time following contractions in rat fast‐(mixed gastrocnemius, MG) and slow‐(soleus, SOL) twitch muscles.MethodsIn twenty Sprague‐Dawley rats (male (n=5), female (n=8) and ovariectomized female (F‐OVX; n=7)), PO2is was determined, before and after GLI superfusion (5 mg kg−1), via phosphorescence quenching (G4). Measurements were taken for 3 min throughout the duration of, and 3 min following, the cessation of electrically‐induced contractions (180 s, 1 Hz, 7V). Blood flow was measured via fluorescent‐labeled microspheres in the last 30 seconds of contractions (15 μm).ResultsIn both muscles, PO2is recovered to its precontracting level in control and GLI conditions within the 3 min measurement window. However, GLI significantly slowed PO2is recovery following contractions in the MG (T63: 87.7 ± 4.6 vs 117.4 ± 7.9 s; p &lt; 0.05), but not in the SOL (73.7 ± 8.8 vs 84.8 ± 11.2 s; p &gt; 0.05). The PO2is value at which T63 occurred was not significantly different between the control and GLI conditions for MG or SOL. During contractions, blood flow was attenuated in the MG following GLI (53 ± 4 vs 39 ± 3 ml/100 g/min; p &lt; 0.05), but not in the SOL (37 ± 4 vs 35 ± 5; p &gt; 0.05).ConclusionThese data highlight the role of KATP channel function in supporting PO2is recovery of fast‐twitch oxidative fiber types due in part to elevated blood flow. These effects of sulphonylurea medication (i.e. GLI) may explain, in part, the early onset of exhaustion in patients performing high‐intensity exercise and/or activities of daily living that recruit fast‐twitch muscles.Support or Funding InformationSupported by NIH Grants: HL108328 (T.I.M and D.C.P) and F31HL145981 (T.D.C)

Phosphoproteomics reveals conserved exercise-stimulated signaling and AMPK regulation of store-operated calcium entry.

Exercise stimulates cellular and physiological adaptations that are associated with widespread health benefits. To uncover conserved protein phosphorylation events underlying this adaptive response, we performed mass spectrometry-based phosphoproteomic analyses of skeletal muscle from two widely used rodent models: treadmill running in mice and insitu muscle contraction in rats. We overlaid these phosphoproteomic signatures with cycling in humans to identify common cross-species phosphosite responses, as well as unique model-specific regulation. We identified >22,000 phosphosites, revealing orthologous protein phosphorylation and overlapping signaling pathways regulated by exercise. This included two conserved phosphosites on stromal interaction molecule 1 (STIM1), which we validate as AMPK substrates. Furthermore, we demonstrate that AMPK-mediated phosphorylation of STIM1 negatively regulates store-operated calcium entry, and this is beneficial for exercise in Drosophila. This integrated cross-species resource of exercise-regulated signaling in human, mouse, and rat skeletal muscle has uncovered conserved networks and unraveled crosstalk between AMPK and intracellular calcium flux.

Sexual dimorphism in the control of skeletal muscle interstitial Po2 of heart failure rats: effects of dietary nitrate supplementation.

Sex differences in the mechanisms underlying cardiovascular pathophysiology of O2 transport in heart failure (HF) remain to be explored. In HF, nitric oxide (NO) bioavailability is reduced and contributes to deficits in O2 delivery-to-utilization matching. Females may rely more on NO for cardiovascular control and as such experience greater decrements in HF. We tested the hypotheses that moderate HF induced by myocardial infarction would attenuate the skeletal muscle interstitial Po2 response to contractions (Po2is; determined by O2 delivery-to-utilization matching) compared with healthy controls and females would express greater dysfunction than male counterparts. Furthermore, we hypothesized that 5 days of dietary nitrate supplementation (Nitrate; 1 mmol·kg-1·day-1) would raise Po2is in HF rats. Forty-two Sprague-Dawley rats were randomly assigned to healthy, HF, or HF + Nitrate groups (each n = 14; 7 female/7 male). Spinotrapezius Po2is was measured via phosphorescence quenching during electrically induced twitch contractions (180 s; 1 Hz). HF reduced resting Po2is for both sexes compared with healthy controls (P < 0.01), and females were lower than males (14 ± 1 vs. 17 ± 2 mmHg) (P < 0.05). In HF both sexes expressed reduced Po2is amplitudes following the onset of muscle contractions compared with healthy controls (female: -41 ± 7%, male: -26 ± 12%) (P < 0.01). In HF rats, Nitrate elevated resting Po2is to values not different from healthy rats and removed the sex difference. Female HF + Nitrate rats expressed greater resting Po2is and amplitudes compared with female HF (P < 0.05). In this model of moderate HF, O2 delivery-to-utilization matching in the interstitial space is diminished in a sex-specific manner and dietary nitrate supplementation may serve to offset this reduction in HF rats with greater effects in females. NEW & NOTEWORTHY Interstitial Po2 (Po2is; indicative of O2 delivery-to-utilization matching) determines, in part, O2 flux into skeletal muscle. We show that heart failure (HF) reduces Po2is at rest and during skeletal muscle contractions in rats and this negative effect is amplified for females. However, elevating NO bioavailability with dietary nitrate supplementation increases resting Po2is and alters the dynamic response with greater efficacy in female HF rats, particularly at rest and following the onset of muscle contractions.

Ovariectomy and obesity have equal impact in causing mitochondrial dysfunction and impaired skeletal muscle contraction in rats

Previous studies have demonstrated that either an obese-insulin resistance condition or a condition involving loss of estrogen impaired skeletal muscle function as indicated by a decrease in muscle contraction. The differing effects of combined estrogen deficiency over obese-insulin resistance on skeletal muscle function have, however, not yet been determined. Our hypothesis was that estrogen deficiency aggravates skeletal muscle dysfunction in obese-insulin resistant rats, via increased muscle oxidative stress and mitochondrial dysfunction. Twenty-four female Wistar rats were divided into 2 groups and animals in each group were fed either a normal diet (ND) or a high-fat diet (HFD) for 24 weeks. At week 13, rats in each group were subdivided into 2 subgroups: sham-operated or ovariectomized (n = 6/subgroup). At the end of the experimental period the contraction of the gastrocnemius muscles was tested before the rats were sacrificed. Skeletal muscle was removed to assess oxidative stress and mitochondrial function. We found that an obese-insulin resistant condition was observed in sham-operated HFD-fed rats, ovariectomized ND-fed rats, and ovariectomized HFD-fed rats. Skeletal muscle contractile function (peak-force ratio [g/g]; 25.40 ± 2.03 [ovariectomized ND-fed rats], 22.44 ± 0.85 [sham-operated HFD-fed rats] and 25.06 ± 0.61 [ovariectomized HFD-fed rats]), skeletal muscle mitochondrial function, and oxidative stress were equally significantly impaired in all 3 groups, when compared with those of sham-operated ND-fed rats (31.12 ± 1.88 g/g [NDS]; P < 0.05). Surprisingly, loss of estrogen did not aggravate these dysfunctions of skeletal muscles in HFD-fed rats. These findings suggest that skeletal muscle dysfunction may occur due to increased muscle oxidative stress and mitochondrial dysfunction as a result of ovariectomy and obese-insulin resistance. Loss of estrogen, however, did not aggravate these impairments in the muscle of rats with obese-insulin resistant condition.

Deep Tissue Incision Enhances Spinal Dorsal Horn Neuron Activity During Static Isometric Muscle Contraction in Rats

Translational correlates to pain with activities after deep tissue injury have been rarely studied. We hypothesized that deep tissue incision causes greater activation of nociception-transmitting neurons evoked by muscle contraction. In vivo neuronal activity was recorded in 203 dorsal horn neurons (DHNs) from 97 rats after sham, skin-only, or skin + deep muscle incision. We evaluated DHN responses to static, isometric muscle contractions induced by direct electrical stimulation of the muscle. The effect of pancuronium on DHN response to contractions was also examined. Approximately 50% of DHNs with receptive fields in the hindpaw were excited during muscle contraction. One-second .5- and 1.0-g muscle contractions produced greater DHN activity after skin + deep muscle incision (median [interquartile range], 32 [5–39] impulses, P = .021; and 36 [26–46] impulses, P = .006, respectively) than after sham (6 [0–21] and 15 [8–32] impulses, respectively). Neuromuscular blockade with pancuronium inhibited the muscle contractions and DHN activation during electrical stimulation, demonstrating contraction-induced activation. The greater response of spinal DHNs to static muscle contraction after skin + deep muscle incision may model and inform mechanisms of dynamic pain after surgery. PerspectiveCompletion of various activities is an important milestone for recovery and hospital discharge after surgery. Skin + deep muscle incision caused greater activation of nociception-transmitting DHNs evoked by muscle contraction compared with skin-only incision. This result suggests an important contribution of deep muscle injury to activity-evoked hyperalgesia after surgery.

PO-126 Inhibition of HIF-1α Alleviates Exaggerated Pressor Response Induced by Static Muscle Contraction in Rats with Peripheral Arterial Disease

Objective Hypoxia-inducible factor 1α (HIF-1α) is a transcription factor mediating adaptive responses to hypoxia and ischemia. A prior work showed that HIF-1α is increased in sensory nerves of rats with femoral artery occlusion. The present study was to examine if the reflex response of blood pressure induced by muscle contraction was altered after injection of HIF-1α inhibitor BAY 87-2243 (BAY87) into the arterial blood supply of the ischemic hindlimb muscles. &#x0D; Methods A rat model of femoral artery ligation was used to study peripheral artery disease. Western blot analysis was employed to examine the protein levels of HIF-1α in the dorsal root ganglion (DRG) tissues. The exercise pressor reflex was evoked by static muscle contraction. &#x0D; Results HIF-1α was increased in the DRG of occluded limbs (optical density: 0.89±0.13 in control vs. 1.5±0.05 in occlusion; P &lt; 0.05, n=6 in each group). Arterial injection of BAY87 (0.2 mg/kg) inhibited expression of HIF-1α in the DRG of occluded limbs three hours following its injection (optical density: 1.02±0.09 in occluded limbs with BAY87 vs. 1.06±0.1 in control limbs; P &gt; 0.05, n=5 in each group). In addition, muscle contraction evoked a greater increase in blood pressure in occluded rats. BAY87 attenuated the enhanced pressor response in occluded rats to a greater degree than in control rats.&#x0D; Conclusions Inhibition of HIF-1α alleviates exaggeration of the exercise pressor reflex in rats under ischemic circumstances of the hindlimbs induced by femoral artery occlusion. &#x0D;

S-adenosyl methionine regulates calcium channels and inhibits uterine smooth muscle contraction in rats with infectious premature delivery through the transient receptor protein 3/protein kinase Cβ/C-kinase-activated protein phosphatase-1 inhibitor of 17 kDa signaling pathway.

The aim of the present study was to investigate the effects of S-adenosyl methionine (SAMe) on infectious premature inflammatory factors and uterine contraction, and to further explore its mechanism of action via the transient receptor protein 3 (TRPC3)/protein kinase Cβ (PKCβ)/C-kinase-activated protein phosphatase-1 inhibitor of 17 kDa (CPI-17) signaling pathway, following intervention by a TRPC3 inhibitor. A rat model of premature delivery induced by lipopolysaccharide (LPS) was established. Following treatment with SAMe and inhibiting TRPC3 expression, rat serum and uterus were isolated. Hematoxylin and eosin staining was used to observe the histopathological changes in the uterus. Uterine muscle strips in vitro were selected to measure the changes in muscle tension. ELISA was utilized to measure the changes in serum inflammatory factor and oxidative stress indexes. Immunohistochemistry, western blot assay and reverse transcription-quantitative polymerase chain reaction were applied to detect calcium channel protein expression in the uterus. Western blot analysis was employed to measure the expression of TRPC3/PKCβ/CPI-17 signaling pathway-related proteins. TRPC3 was highly expressed in the uterus of rat models of premature delivery induced by LPS. Following treatment with SAMe, inflammatory cell infiltration markedly reduced in the uterus and the tension of in vitro uterine muscle strips significantly decreased. SAMe treatment suppressed inflammatory reaction and oxidative stress, and diminished L-type and T-type calcium channel protein expression. TRPC3/PKCβ/CPI-17 signaling pathway-related protein expression was also reduced. When TRPC3 expression was suppressed, the effects of SAMe against inflammation and oxidative stress were diminished. TRPC3/PKCβ/CPI-17 signaling pathway-related protein expression significantly increased. SAMe was able to reduce inflammatory reaction and oxidative stress in the uterus of rat model of infectious premature delivery induced by LPS, prolong delivery time, reduce the mortality rate of offspring rats, and serve a therapeutic role. This effect is likely achieved via the regulation of uterine contractions and childbirth through the TRPC3/PKCβ/CPI-17 signaling pathway.

Exercise (In)Tolerance in Sickle Cell Disease: Potential Disruptive Role of Free Hemoglobin on Skeletal Muscle Oxygen Delivery/Utilization Matching and Functional Capacity

Sickle cell disease (SCD) reduces exercise tolerance likely due to vascular and skeletal muscle abnormalities stemming from increased free hemoglobin (Hb, a known scavenger of nitric oxide). However, there has been little advancement in our understanding of the precise mechanisms responsible for the reduction in physical functionality. Therefore, the purpose of this investigation was 1) determine the degree by which exercise tolerance is impaired in a mouse model of SCD (BERK) and 2) examine the impact of free Hb on the skeletal muscle microvascular PO2 (PO2mv, the principal driving force that facilitates blood-muscle O2 flux) at rest and during muscle contractions in rats exposed to acutely elevated free [Hb]. We hypothesized that exercise capacity, as measured by the running speed/exercise duration relationship (critical speed, CS), would be lower in BERK relative to wild-type mice (WT) with a lower PO2mv observed during muscle contractions following Hb infusion. Twenty female mice (WT, n=10 and BERK, n=10) performed 4 constant-speed treadmill tests that resulted in fatigue within 1.5 to 20 min. Time to fatigue vs. treadmill speed were fit to a hyperbolic model to determine CS. PO2mv was measured (phosphorescence quenching) at rest and during 180 s of electrically induced (1-Hz) spinotrapezius muscle contractions during control, following free Hb infusion (Hb, 50 mg), and L-nitro arginine methyl ester superfusion (L-NAME, 1.5 mM) conditions in 9 rats. Speed and time to exhaustion for WT and BERK conformed to a hyperbolic relationship (WT: r2 = 0.93 ± 0.02, BERK: r2 = 0.97 ± 0.01, p>0.05). CS was significantly lower in BERK when compared to WT (WT: 33.1 ± 1.5, BERK: 25.2 ± 0.7 m/min, p<0.05). Following the onset of muscle contractions, Hb and L-NAME significantly increased the amplitude of the fall in PO2mv when compared to control, with no significant differences between Hb and L-NAME conditions (Δ1PO2mv: control: 9.5±0.7, Hb: 11.7±1, L-NAME 10.4±0.8 mmHg, p<0.05). The increased Δ1PO2mv resulted in a significantly lower PO2mv during the steady-state of muscle contractions in both Hb and L-NAME conditions, with no differences between Hb and L-NAME (PO2mv(steady-state): control: 24.1±0.9, Hb: 21.3±0.7, L-NAME: 19.6±1 mmHg, p<0.05). To summarize, exercise tolerance, as measured via CS, was significantly lower in BERK mice relative to WT. Furthermore, the lower PO2mv(steady-state) in Hb and L-NAME represents a compromised blood-myocyte O2 driving force during muscle contractions. Collectively, these data suggest that SCD impacts physical capacity via a disruption in the tight matching between oxygen delivery and utilization within the skeletal muscle and that this dysfunction could be mediated by a reduced nitric oxide bioavailability consequent of elevated free [Hb]. Support or Funding Information Funded by NIH (R01HL125642) to DCI and Colorado Nutrition and Obesity Research Center (P30DK048520) award to SKF. Mean percent PO2mv for the spinotrapezius muscle for control, Hb, and L-NAME conditions. Time “zero” represents the onset of electrically stimulated 1-hz twitch muscle contractions. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of 3-substituted 1,4-benzodiazepin-2-ones on bradykinin-induced smooth muscle contraction.

Biochemical properties of 3-substituted 1,4-benzodiazepine determined by the characteristics of their chemical structure. Influence of 3-substituted 1,4-benzodiazepin-2-ones on maximal normalized rate and amplitudes of isometric smooth muscle contraction in rats was investigated. Compounds MX-1775 and MX-1828 demonstrated the similar inhibition effect on bradykinin-induced contraction of smooth muscle like competitive inhibitor des-arg9-bradykinin-acetate to bradykinin B2-receptors. MX-1626 demonstrated unidirectional changes of maximal normalized rate and force of smooth muscle that proportionally depended on bradykinin concentration in the range 10-10-10-6 M. MX-1828 has statistically significant decrease of normalized rate of smooth muscle contraction for bradykinin concentrations 10-10 and 10-9 M by 20.7 and 8.6%, respectively, but for agonist concentration 10-6 M, this parameter increased by 10.7% and amplitude was reduced by 29.5%. Compounds MX-2011, MX-1785 and MX-2004 showed no natural effect on bradykinin-induced smooth muscle contraction. Compounds MX-1775, MX-1828, MX-1626 were selected for further research of their influence on kinin-kallikrein system and pain perception.

Effects of magnesium sulfate on airway smooth muscle contraction in rats.

Aim To investigate the effect of magnesium sulfate (MgSO4) at different doses on isolated tracheal smooth muscle contraction in rats induced by different mechanisms. Methods Twelve rats' tracheas were placed into organ bath. Consecutively, acetylcholine (10-6,10-5,10-4 M), histamine(10-8,10-5,10-3 M) and KCl (30,60 mM) solutions was administered for contractions. MgSO4 from 10-4 to 10-1 M concentrations were subsequently administered after each constrictive agent and relaxation degrees were recorded. Results In the acetylcholine and KCl groups, dose dependent strong contractions were observed, but not in the histamine group and that group was excluded. Significant relaxation occurred with gradually increasing doses of MgSO4. In the high dose KCl group, a slight increase in contractions after the administration of 10-4 and 10-3 M MgSO4 was recorded. Conclusion We suggest that MgSO4 is effective in relaxing airway smooth muscle contractions caused by different factors; however, it must be considered that low doses of MgSO4 may only lead to a slight increase in contractions.