Arteriolar responses to vasodilator stimuli and elevated P(O2) in renin congenic and Dahl salt-sensitive rats

OBJECTIVES: Angiotensin II suppression leads to impaired vascular relaxation in normotensive animals on a high-salt diet. The goal of this study was to determine whether normal vascular reactivity could be restored by transferring the chromosomal region carrying the Dahl salt-resistant (R) renin gene into the Dahl salt-sensitive (SS) genetic background in a strain of renin congenic rats (RGRR). METHODS: Male RGRR and SS rats were fed low-salt (0.4%) and high-salt (4%) diets for 4 weeks. The responses of cremaster muscle arterioles to acetylcholine (ACh), sodium nitroprusside (SNP), and elevated PO2 were assessed using video microscopy. RESULTS: ACh-induced dilation was significantly enhanced in RGRR on a high-salt diet compared to SS rats, while dilation to the NO donor SNP was similar in both strains. A high-salt diet significantly enhanced arteriolar constriction in response to elevated PO2, in both SS and RGRR rats. CONCLUSIONS: These data suggest that transfer of the chromosomal region containing the renin gene is crucial in the recovery of ACh-induced dilation of arterioles in RGRR rats vs. SS rats, and that factors in the SS genetic background contribute to an enhanced sensitivity to elevated PO2, independent of genes on chromosome 13.     

Hand‐held Dynamometer Positioning Impacts Discomfort During Quadriceps Strength Testing: A Validity and Reliability Study

Purpose/Background

A belt‐stabilized hand‐held dynamometer (HHD) offers the ability to quantify quadriceps muscle strength in a clinical environment, but a limitation is participant discomfort at the interface between the HHD and the tibia. The purpose of this study was to quantify the level of discomfort associated with a modified belt‐stabilized HHD configuration compared to a standard belt‐stabilized configuration and an isokinetic dynamometer. The secondary purpose of this study was to determine the validity and reliability of a modified configuration used to measure quadriceps strength compared to the “gold‐standard” isokinetic dynamometer.

Methods

Twenty healthy participants (5 males, 15 females; age=24.7±2.2 years, height=171.1±8.8 cm, mass=72.0±18.7 kg) performed maximal knee extension isometric contractions during each of three testing conditions: isokinetic dynamometer, standard configuration with HHD placement on the tibia, and an alternative configuration with the HHD interfaced with the leg of a table. Discomfort was quantified using a Visual Analog Scale (VAS). Differences in discomfort and torque (N•m) associated with the testing positions were determined using Friedman test or repeated measures analysis of variance. Validity was quantified using Pearson correlations and within‐session intrarater reliability was determined using an intraclass correlation coefficient (ICC2,1) and associated confidence intervals (95% CI).

Results

The isokinetic dynamometer configuration resulted in the least discomfort (p< .01) and the modified configuration was more comfortable than the standard configuration (p= .003). There was a significant correlation between measures from the isokinetic dynamometer and the standard configuration (r=.87) and modified configuration (r=.93). Within‐session intrarater reliability was good for both the standard configuration (ICC_2,1=0.93) and modified configuration (ICC_2,1=0.93) conditions.

Conclusions

The use of the modified belt‐stabilized HHD configuration, where the HHD was interfaced with the leg of a table, offers a more comfortable alternative compared to the standard belt‐stabilized configuration to obtain isometric quadriceps strength measures in a clinical environment. This configuration is also a valid and reliable alternative to the “gold standard” isokinetic dynamometer when testing isometric quadriceps strength at 90° of knee flexion.

Level of Evidence

Diagnostic, Level 3     

Functional recovery of denervated muscle by neurotization using nerve guidance channels

Tissue‐engineered muscle has been proposed as a means of repairing volumetric muscle defects to restore anatomical and functional recovery. We have previously demonstrated that denervated muscle, which is analogous to engineered muscle construct, can be reinnervated by direct transplantation of host nerve (neurotization) in a rat model. However, the use of this approach is not possible if the length of host nerve is inadequate and cannot be mobilized to the insertion site of the engineered muscle. In this study we investigated whether neurotization coupled with nerve guidance channels would increase the regeneration of neuromuscular junctions (NMJs) in completely denervated muscle and encourage neurofunctional recovery. Seventy‐two Lewis rats were evaluated in three groups, a normal control group (n = 8), a denervated group (n = 32) and a neurotization coupled with nerve guidance group (n = 32). Neurofunctional behaviour and histological evaluations were performed at 4, 8, 12 and 20 weeks postoperatively. Extensor postural thrust (EPT) and compound muscle action potential (CMAP) amplitude were significantly improved in the nerve guidance group when compared with the denervated group, even though these values were different from those of the normal control group at 20 weeks postoperation. Regeneration of axons and NMJs was demonstrated histologically in the nerve guidance group. Neurotization coupled with nerve guidance channels leads to regeneration of axons and NMJs in completely denervated muscle. To our knowledge, this is the first report to show that nerve guidance can allow re‐innervation in denervated muscle containing long‐gap nerve injuries. Copyright © 2013 John Wiley & Sons, Ltd.