Efficacy and safety of hydrokinesitherapy in patients with dystrophinopathy

Duchenne muscular dystrophy (DMD) is one of the most common forms of hereditary muscular dystrophies in childhood and is characterized by steady progression and early disability. It is known that physical therapy can slow down the rate of progression of the disease. According to global recommendations, pool exercises, along with stretching, are preferable for children with DMD, as these types of activities have a balanced effect on skeletal muscles and allow simultaneous breathing exercises. The present study aimed to evaluate the effectiveness of regular pool exercises in patients with Duchenne muscular dystrophy who are capable of independent movement during 4 months of training. 28 patients with genetically confirmed Duchenne muscular dystrophy, who were aged 6.9 ± 0.2 years, were examined. A 6-min distance walking test and timed tests, namely, rising from the floor, 10-meter running, and stair climbing and descending, muscle strength of the upper and lower extremities were assessed on the baseline and during dynamic observation at 2 and 4 months. Hydrorehabilitation course lasted 4 months and was divided into two stages: preparatory and training (depend on individual functional heart reserve (IFHR)). Set of exercises included pool dynamic aerobic exercises. Quantitative muscle MRI of the pelvic girdle and thigh was performed six times: before training (further BT) and after training (further AT) during all course. According to the results of the study, a statistically significant improvement was identified in a 6-min walking test, with 462.7 ± 6.2 m on the baseline and 492.0 ± 6.4 m after 4 months (p < 0.001). The results from the timed functional tests were as follows: rising from the floor test, 4.5 ± 0.3 s on the baseline and 3.8 ± 0.2 s after 4 months (p < 0.001); 10 meter distance running test, 4.9 ± 0.1 s on the baseline and 4.3 ± 0.1 s after 4 months (p < 0.001); 4-stair climbing test, 3.7 ± 0.2 s on the baseline and 3.2 ± 0.2 s after 4 months (p < 0.001); and 4-stair descent test, 3.9 ± 0.1 s on the baseline and 3.2 ± 0.1 s after 4 months (p < 0.001). Skeletal muscle quantitative MRI was performed in the pelvis and the thighs in order to assess the impact of the procedures on the muscle structure. Muscle water T2, a biomarker of disease activity, did not show any change during the training period, suggesting the absence of deleterious effects and negative impact on disease activity. Thus, a set of dynamic aerobic exercises in water can be regarded as effective and safe for patients with DMD.

Fast, precise, and accurate myocardial T1 mapping using a radial MOLLI sequence with FLASH readout

PURPOSE

Quantitative cardiac MRI, and more particularly T₁ mapping, has become a most important modality to characterize myocardial tissue. In this work, the value of a radial variant of the conventional modified Look-Locker inversion recovery sequence (raMOLLI) is demonstrated.

METHODS

The raMOLLI acquisition scheme consisted of five radial echo trains of 80 spokes acquired using either a fast low-angle shot (FLASH) or a true fast imaging with steady-state-precession (TrueFISP) readout at different time points after a single magnetization inversion. View sharing combined with a compressed sensing algorithm allowed the reconstruction of 50 images along the T₁ relaxation recovery curve, to which a dictionary-fitting approach was applied to estimate T₁ . The sequence was validated on a nine-vial phantom, on 19 healthy subjects, and one patient suffering from dilated cardiomyopathy.

RESULTS

The raMOLLI sequence allowed a significant decrease of myocardial T₁ map acquisition time down to five heartbeats, while exhibiting a higher degree of accuracy and a comparable precision on T₁ value estimation than the conventional modified Look-Locker inversion recovery sequence. The FLASH readout demonstrated a better robustness to B₀ inhomogeneities than TrueFISP, and was therefore preferred for in vivo acquisitions.

CONCLUSIONS

This sequence represents a good candidate for ultrafast acquisition of myocardial T₁ maps. Magn Reson Med 79:1387-1398, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Anatomical and mesoscopic characterization of the dystrophic diaphragm: An in vivo nuclear magnetic resonance imaging study in the Golden retriever muscular dystrophy dog

Because respiratory failure remains a major issue in Duchenne Muscular Dystrophy patients, respiratory muscles are a key target of systemic therapies. In the Golden Retriever Muscular Dystrophy (GRMD) dogs, the disease shows strong clinical and histological similarities with the human pathology, making it a valuable model for preclinical therapeutic trials. We report here the first nuclear magnetic resonance (NMR) imaging anatomical study of the diaphragm in GRMD dogs and healthy controls. Both T1- and T2-weighted images of the diaphragm of seven healthy and thirteen GRMD dogs, from 3 to 36 months of age, were acquired on a 3 tesla NMR scanner. Abnormalities of texture and shape were revealed and consisted of increases in signal intensity on T2-weighted images and in signal heterogeneity on both T1- and T2-weighted images of the dystrophic diaphragm. These abnormalities were associated with a significant thickening of the muscle and we identified a clear 8-mm-threshold distinguishing clinically preserved GRMD dogs from those more severely affected. In this study, we demonstrated the feasibility of NMR imaging of the diaphragm and depicted several anatomical and mesoscopic anomalies in the dystrophic diaphragm. NMR imaging of the diaphragm shows a promise as an outcome measure in preclinical trials using GRMD dogs.

Quantitative ultrashort TE imaging of the short-T2 components in skeletal muscle using an extended echo-subtraction method

PURPOSE

To introduce an ultrashort echo time (UTE) based method for quantitative mapping of short-T₂ signals in skeletal muscle (SKM) in the presence of fat, with the aim of monitoring SKM fibrosis.

METHODS

From a set of at least five UTE images of the same slice, a long- T2* map, a fat-fraction map, and a map of short-T₂ -signal fraction are extracted. The method was validated by numerical simulations and in vitro studies on collagen solutions. Finaly, the method was applied to image the short-T₂ signals in the leg of eight healthy volunteers.

RESULTS

The imaged short-T₂ -signal fractions in the collagen solutions correlated with their respective collagen concentrations ( R=0.999,  P=0.009). Short-T₂ tissues such as cortical bone and fasciae were highlighted in the resulting short-T₂ fraction maps. A significant fraction of short-T₂ signal was systematically observed in the skeletal muscle of all of the subjects (4.5±1.2%).

CONCLUSION

The proposed method allows the quantitative imaging of short-T₂ components in tissues containing fat. By also having the fat-fraction and T2* maps as outcomes, long-T₂ suppression is accomplished without requiring modifications to the basic UTE sequence. Although the hypersignal observed in the fasciae suggests that the short-T₂ signal observed in SKM might arise from interstitial connective tissue, further investigation is necessary to confirm this statement. Magn Reson Med 78:997-1008, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Sepsis induces long-term metabolic and mitochondrial muscle stem cell dysfunction amenable by mesenchymal stem cell therapy

Sepsis, or systemic inflammatory response syndrome, is the major cause of critical illness resulting in admission to intensive care units. Sepsis is caused by severe infection and is associated with mortality in 60% of cases. Morbidity due to sepsis is complicated by neuromyopathy, and patients face long-term disability due to muscle weakness, energetic dysfunction, proteolysis and muscle wasting. These processes are triggered by pro-inflammatory cytokines and metabolic imbalances and are aggravated by malnutrition and drugs. Skeletal muscle regeneration depends on stem (satellite) cells. Herein we show that mitochondrial and metabolic alterations underlie the sepsis-induced long-term impairment of satellite cells and lead to inefficient muscle regeneration. Engrafting mesenchymal stem cells improves the septic status by decreasing cytokine levels, restoring mitochondrial and metabolic function in satellite cells, and improving muscle strength. These findings indicate that sepsis affects quiescent muscle stem cells and that mesenchymal stem cells might act as a preventive therapeutic approach for sepsis-related morbidity.

Sepsis patients often develop muscle atrophy that can last for years. Here the authors show in a mouse model that sepsis causes long-term impairment of the satellite cells, affecting mitochondrial function and energy metabolism, and that injection of mesenchymal stem cells restores satellite cell metabolism and muscle regeneration.

Measuring perfusion and bioenergetics simultaneously in mouse skeletal muscle: a multiparametric functional-NMR approach

A totally noninvasive set-up was developed for comprehensive NMR evaluation of mouse skeletal muscle function in vivo. Dynamic pulsed arterial spin labeling-NMRI perfusion and blood oxygenation level-dependent (BOLD) signal measurements were interleaved with (31)P NMRS to measure both vascular response and oxidative capacities during stimulated exercise and subsequent recovery. Force output was recorded with a dedicated ergometer. Twelve exercise bouts were performed. The perfusion, BOLD signal, pH and force-time integral were obtained from mouse legs for each exercise. All reached a steady state after the second exercise, justifying the pointwise summation of the last 10 exercises to compensate for the limited (31)P signal. In this way, a high temporal resolution of 2.5  s was achieved to provide a time constant for phosphocreatine (PCr) recovery (τ(PCr)). The higher signal-to-noise ratio improved the precision of τ(PCr) measurement [coefficient of variation (CV) = 16.5% vs CV = 49.2% for a single exercise at a resolution of 30  s]. Inter-animal summation confirmed that τ(PCr) was stable at steady state, but shorter (89.3 ± 8.6  s) than after the first exercise (148  s, p < 0.05). This novel experimental approach provides an assessment of muscle vascular response simultaneously to energetic function in vivo. Its pertinence was illustrated by observing the establishment of a metabolic steady state. This comprehensive tool offers new perspectives for the study of muscle pathology in mice models.

Discrepancies between the fate of myoblast xenograft in mouse leg muscle and NMR label persistency after loading with Gd-DTPA or SPIOs

1H-NMR (nuclear magnetic resonance) imaging is regularly proposed to non-invasively monitor cell therapy protocols. Prior to transplantation, cells must be loaded with an NMR contrast agent (CA). Most studies performed so far make use of superparamagnetic iron oxide particles (SPIOs), mainly for favorable detection sensitivity. However, in the case of labeled cell death, SPIO recapture by inflammatory cells might introduce severe bias. We investigated whether NMR signal changes induced by preloading with SPIOs or the low molecular weight gadolinium (Gd)-DTPA accurately monitored the outcome of transplanted cells in a murine model of acute immunologic rejection. CA-loaded human myoblasts were grafted in the tibialis anterior of C57BL/6 mice. NMR imaging was repeated regularly until 3 months post-transplantation. Label outcome was evaluated by the size of the labeled area and its relative contrast to surrounding tissue. In parallel, immunohistochemistry assessed the presence of human cells. Data analysis revealed that CA-induced signal changes did not strictly reflect the graft status. Gd-DTPA label disappeared rapidly yet with a 2-week delay compared with immunohistochemical evaluation. More problematically, SPIO label was still visible after 3 months, grossly overestimating cell survival (<1 week). SPIOs should be used with extreme caution to evaluate the presence of grafted cells in vivo and could hardly be recommended for the long-term monitoring of cell transplantation protocols.

Characterization of dystrophic muscle in golden retriever muscular dystrophy dogs by nuclear magnetic resonance imaging

The Golden Retriever Muscular Dystrophy dog lacks dystrophin. Disease progression in this model shares many similarities with the Duchenne muscular dystrophy, both from anatomico pathological and clinical standpoints. The model is increasingly used in pre-clinical trials but needs to be further investigated, particularly with reference to the evaluation of therapies. The aim of this study was to identify quantitative indices that would help characterize the dystrophic dog non-invasively using NMR imaging. Two-month-old dystrophic dogs and healthy control animals were scanned at 4T. Standard T2- and T1-weighted images, fat-saturated T1-weighted images pre- and post-gadolinium chelate injection were acquired and kinetics of muscle enhancement were studied over a 2-h period. Several indices were found to be abnormally high in dystrophic dogs: the T2-weighted/T1-weighted signal ratio, T2-weighted image heterogeneity and maximal signal enhancement post-gadolinium. These may be proposed to evaluate muscle structural alterations non-invasively in this disease.

Muscle blood flow and oxygenation measured by NMR imaging and spectroscopy

Tissue perfusion and oxygenation in many organs can be evaluated by various NMR techniques. This review focuses on the specificities, limitations and adaptations of the NMR tools available to investigate perfusion and oxygenation in the skeletal muscle of humans and animal models. A description of how they may be used simultaneously is provided as well. 1H NMR spectroscopy of myoglobin (Mb) monitors intramyocytic oxygenation. It measures the level of deoxy-Mb, from which Mb concentration, Mb desaturation/resaturation rates, muscle oxygenation changes and intracellular partial oxygen pressure (pO2) can be calculated. Positive and negative blood oxygen level-dependent (BOLD) contrasts exist in skeletal muscle. BOLD contrasts primarily reflect changes in capillary-venous oxygenation, but are also directly or indirectly dependent on muscle blood volume, perfusion, vascular network architecture and angulation, relative to the main magnetic field. Arterial spin labelling (ASL) techniques, having high spatial and temporal resolution, are the methods of choice to quantify and map skeletal muscle perfusion non-invasively. Limitations of ASL are poor contrast-to-noise ratio and sensitivity to movement; however, with the introduction of specific adaptations, it has been proven possible to measure skeletal muscle perfusion at both rest and during exercise. The possibility of combining these NMR measurements with others into a single dynamic protocol is most interesting. The 'multiparametric functional (mpf) NMR' concept can be extended to include the evaluation of muscle energy metabolism simultaneously with 31P NMR or with lactate double quantum filtered 1H NMR spectroscopy, an approach which would make NMR an exceptional tool for non-invasive investigations of integrative physiology and biochemistry in skeletal muscle in vivo.

Influence of vascular filling and perfusion on BOLD contrast during reactive hyperemia in human skeletal muscle

Mechanisms generating BOLD contrast are complex and depend on parameters that are prone to large variations, in particular in skeletal muscle. Here, we simultaneously measured perfusion by ASL, and BOLD response in the calf muscle of 6 healthy volunteers during post-ischemic reactive hyperemia. We tested whether the relation between the two was altered for varying degrees of leg vascular replenishment induced by prior positioning of the leg at different heights relative to the heart. We found that the BOLD response depended on perfusion, but also on the degree of repletion of leg blood vessels. We conclude that simultaneous determination of perfusion by ASL is important to identify the mechanisms underlying BOLD contrast in the skeletal muscle.

In vivo NMR imaging evaluation of efficiency and toxicity of gene electrotransfer in rat muscle

In vivo gene electrotransfer (ET) is a simple method of gene delivery in various tissues relying on the injection of plasmid DNA followed by application of electric pulses. Noninvasive tools are needed to evaluate the ET efficiency and the resulting tissue damages. In this study, we performed ET of rat tibialis muscle after injection of either a plasmid coding for luciferase or a contrast agent (CA) detected by using magnetic resonance imaging (MRI). Plasmid expression and CA intracellular trapped quantity were compared throughout the electric field intensity range 0-300 V/cm. Although the CA trapped quantity reflects only the electropermeabilization step, both measurements were correlated. MRI measurements gave easy access to tridimensional visualization of the labelled zones where the CA has been injected and the applied electric field had a value allowing permeabilization. We also performed MRI measurements of the water transverse relaxation time T2 as an indicator of tissue modification, and tested whether another CA specific for necrosis could be used to detect muscle necrosis at high electric field intensity. In conclusion, MRI measurements may bring multiparametric information upon the efficiency and tissue toxicity of an ET protocol by using a simple and safe CA.

Metabolic and vascular support for the role of myoglobin in humans: a multiparametric NMR study

In human muscle the role of myoglobin (Mb) and its relationship to factors such as muscle perfusion and metabolic capacity are not well understood. We utilized nuclear magnetic resonance (NMR) to simultaneously study the Mb concentration ([Mb]), perfusion, and metabolic characteristics in calf muscles of athletes trained long term for either sprint or endurance running after plantar flexion exercise and cuff ischemia. The acquisitions for 1H assessment of Mb desaturation and concentration, arterial spin labeling measurement of muscle perfusion, and 31P spectroscopy to monitor high-energy phosphate metabolites were interleaved in a 4-T magnet. The endurance-trained runners had a significantly elevated [Mb] (0.28 ± 0.06 vs. 0.20 ± 0.03 mmol/kg). The time constant of creatine rephosphorylation (τPCr), an indicator of oxidative capacity, was both shorter in the endurance-trained group (34 ± 6 vs. 64 ± 20 s) and negatively correlated with [Mb] across all subjects ( r = 0.58). The time to reach maximal perfusion after cuff release was also both shorter in the endurance-trained group (306 ± 74 vs. 560 ± 240 s) and negatively correlated with [Mb] ( r = 0.56). Finally, Mb reoxygenation rate tended to be higher in the endurance-trained group and was positively correlated with τPCr ( r = 0.75). In summary, these NMR data reveal that [Mb] is increased in human muscle with a high oxidative capacity and a highly responsive vasculature, and the rate at which Mb resaturates is well correlated with the rephosphorylation rate of Cr, each of which support a teleological role for Mb in O2 transport within highly oxidative human skeletal muscle.

A comparison of voluntary and electrically induced contractions by interleaved 1H- and 31P-NMRS in humans

Skeletal muscle voluntary contractions (VC) and electrical stimulations (ES) were compared in eight healthy men. High-energy phosphates and myoglobin oxygenation were simultaneously monitored in the quadriceps by interleaved (1)H- and (31)P-NMR spectroscopy. For the VC protocol, subjects performed five or six bouts of 5 min with a workload increment of 10% of maximal voluntary torque (MVT) at each step. The ES protocol consisted of a 13-min exercise with a load corresponding to 10% MVT. For both protocols, exercise consisted of 6-s isometric contractions and 6-s rest cycles. For an identical mechanical level (10% MVT), ES induced larger changes than VC in the P(i)-to-phosphocreatine ratio [1.38 +/- 1.14 (ES) vs. 0.13 +/- 0.04 (VC)], pH [6.69 +/- 0.11 (ES) vs. 7.04 +/- 0.07 (VC)] and myoglobin desaturation [43 +/- 15.9 (ES) vs. 6.1 +/- 4.6% (VC)]. ES activated the muscle facing the NMR coil to a greater extent than did VCs when evaluated under identical technical conditions. This metabolic pattern can be interpreted in terms of specific temporal and spatial muscle cell recruitment. Furthermore, at identical levels of energy charge, the muscle was more acidotic and cytoplasm appeared more oxygenated during ES than during VC. These results are in accordance with a preferential recruitment of type II fibers and a relative muscle hyperperfusion during ES.

[Exploration of exercise intolerance by 31P NMR spectroscopy of calf muscles coupled with MRI and ergometry]

One hundred patients presenting with exercise intolerance or rhabdomyolysis episodes have been examined successively by 31P Nuclear Magnetic Resonance Spectroscopy (MRS) of leg plantar flexor muscles with exercise test. In all cases a muscle biopsy was performed. At the end of investigations, diagnosis of a metabolic myopathy was made in 33 patients: glycogenolysis or glycolysis deficiency in 8 cases, mitochondrial myopathy in 24 cases and CPT II deficiency in one case. Muscular dystrophy or congenital myopathy were diagnosed in 6 cases. No precise etiology could be found in 30 patients with either high CK levels or muscle biopsy abnormalities. Seven patients had rhabdomyolysis related to excessive physical activities. Twenty-four patients had functional symptoms. The principal MRS parameters used for diagnosis were the values of intracellular pH at the end of exercise and the time constant of phosphocreatine resynthesis during recovery. Lack of acidosis after exercise was observed in all patients with blockade of glycogenolysis or glycolysis. A slowing in phosphocreatine resynthesis was found in 66 p.cent of patients with definite mitochondrial myopathy. The specificity of these parameters were respectively 92.4 p.cent and 85.5 p.cent for the two groups. In conclusion (31)P MRS allows the detection of muscular glycogenoses with a sensitivity close to 100 p.cent. However, its sensitivity was lower for the detection of mitochondrial myopathies, as is also known for the other in vivo metabolic investigations, reflecting the heterogeneity of expression of mitochondrial abnormalities in a given muscle. The integration of imaging in the examination protocol may help to orientate towards the diagnostic of a dystrophy in some patients.

Determination of skeletal muscle perfusion using arterial spin labeling NMRI: validation by comparison with venous occlusion plethysmography

T(1)-based determination of perfusion was performed with the high temporal and spatial resolution that monitoring of exercise physiology requires. As no data were available on the validation of this approach in human muscles, T(1)-based NMRI of perfusion was compared to standard strain-gauge venous occlusion plethysmography performed simultaneously within a 4 T magnet. Two different situations were investigated in 21 healthy young volunteers: 1) a 5-min ischemia of the leg, or 2) a 2-3 min ischemic exercise consisting of a plantar flexion on an amagnetic ergometer. Leg perfusion was monitored over 5-15 min of the recovery phase, after the air-cuff arterial occlusion had been released. The interesting features of the sequence were the use of a saturation-recovery module for the introduction of a T(1) modulation and of single-shot spin echo for imaging. Spatial resolution was 1.7 x 2.0 mm and temporal resolution was 2 s. For data analysis, ROIs were traced on different muscles and perfusion was calculated from the differences in muscle signal intensity in successive images. To allow comparison with the global measurement of perfusion by plethysmography, the T(1)-based NMR measurements in exercising muscles were rescaled to the leg cross-section. The perfusion measurements obtained by plethysmography and NMRI were in close agreement with a correlation coefficient between 0.87 and 0.92. This indicates that pulsed arterial techniques provide determination of muscle perfusion not only with superior spatial and temporal resolution but also with exactitude.

Comparison of single-shot fast spin-echo and conventional spin-echo sequences for MR imaging of the heart: initial experience

A conventional T1-weighted spin-echo (SE) magnetic resonance (MR) imaging sequence was compared with breath-hold and non-breath-hold half- Fourier single-shot fast SE MR sequences with black-blood preparation and high spatial resolution for imaging of various cardiac diseases. The optimized single-shot fast SE sequence provided better or equal image quality in less time. Breath-hold and non-breath-hold single-shot fast SE sequences may replace the conventional T1-weighted SE sequence for first-line cardiac MR imaging.

Effect of chronic magnesium supplementation on magnesium distribution in healthy volunteers evaluated by 31P-NMRS and ion selective electrodes

AIMS

The role of magnesium (Mg) intake in the prevention and treatment of diseases is greatly debated. Mg biodistribution after chronic Mg supplementation was investigated, using state-of-the-art technology to detect changes in free ionized Mg, both at extra- and intracellular levels.

METHODS

Thirty young healthy male volunteers participated in a randomised, placebo (P)-controlled, double-blind trial. The treated group (MgS) took 12 mmol magnesium lactate daily for 1 month. Subjects underwent in vivo 31P-NMR spectroscopy and complete clinical and biological examinations, on the first and last day of the trial. Total Mg was measured in plasma, red blood cells and 24 h urine ([Mg]U ). Plasma ionized Mg was measured by ion-selective electrodes. Intracellular free Mg concentrations of skeletal muscle and brain tissues were determined noninvasively by in vivo 31P-NMR at 3T. NMR data were automatically processed with the dedicated software MAGAN.

RESULTS

Only [Mg]U changed significantly after treatment (in mmol/24 h, for P, from 4.2+/-1.4 before to 4.1+/-1.3 after and, for MgS, from 3.9+/-1.1 before to 5. 1+/-1.1 after, t=2.15, P=0.04). The two groups did not differ, either before or after the trial, in any other parameter, whether clinical, biological or in relation with the Mg status.

CONCLUSIONS

Chronic oral administration of Mg tablets to young healthy male volunteers at usual pharmaceutical doses does not alter Mg biodistribution. This study shows that an adequate and very complete noninvasive methodology is now available and compatible with the organization of clinical protocols which aim at a thorough evaluation of Mg biodistribution.

Evidence for bi-exponential transverse relaxation of lactate in excised rat muscle

To elucidate the low proton nuclear magnetic resonance (NMR) visibility of muscle lactate previously demonstrated in excised rat muscle, lactate transverse relaxation was investigated in the same model using double quantum editing sequences with effective echo times ranging from 55 to 475 msec. On this time scale, muscle lactate clearly exhibits a bi-exponential transverse relaxation with a short T2 of 33+/-5 msec (mean +/- SE, n = 3) and a long T2 of 230+/-10 msec. The relative populations (84+/-4% vs. 16+/-4%, respectively) of these two lactate pools are compatible with compartmentation between intra- and extracellular muscle lactate.

Evidence of muscle BOLD effect revealed by simultaneous interleaved gradient-echo NMRI and myoglobin NMRS during leg ischemia

The purpose of this work was to investigate the temporal relationship between intensity changes in T2*-weighted NMR images and tissue oxygen content, measured by myoglobin proton NMR spectroscopy, in the skeletal muscle. During an ischemic stress test, the calf muscles of five healthy volunteers were studied at 3 Tesla. An interleaved NMRI-NMRS sequence was used, which made it possible to record T2*-weighted images and myoglobin spectra simultaneously. During ischemia, rapid changes in muscle signal intensity were observed on T2*-weighted images, which immediately preceded myoglobin desaturation. Bearing in mind the respective P50 of hemoglobin and myoglobin, this observation clearly favored the hypothesis that hemoglobin desaturation was responsible for the changes in T2*. This interpretation was further supported by the temporal coincidence between the experimental NMR data and a model of hemoglobin desaturation solely derived from physiological considerations.

Optimized outer volume suppression for single-shot fast spin-echo cardiac imaging

Among the ultrafast MRI techniques, the single-shot fast spin-echo sequence offers a robust alternative to echo planar imaging, essentially because of a much reduced sensitivity to B0 inhomogeneity. This property is particularly appealing in situations in which B0 inhomogeneities can be severe and difficult to correct, such as in cardiac imaging. With single-shot cardiac imaging, however, achieving high resolution over the necessarily large field of views without introducing back-folding artifacts is problematic. One option is to use multishot sequences. However, then issues related to cardiac gating arise. Another solution is to use, optimized presaturation slabs with quadratic phase pulses generated by the Shinnar-LeRoux algorithm. These can be set to reduce the field of view in the phase-encoding direction, resulting in a reduction in the number of phase-encoding steps. For instance, for a 1 x 2-mm spatial resolution, over a rectangular, 250 x 125-mm field of view, and using a half Fourier acquisition, an echo-train length of only 40 is required. With a 4.5-msec echo spacing, the total imaging time is approximately 180 msec. The efficacy of this solution on phantoms and volunteers is demonstrated. Multislice short-axis examinations of the whole heart, realized within a single short breath-hold of approximately 10 seconds, are shown. The possibility of investigating not only cardiac anatomy but also both contractility and myocardial perfusion is discussed.

Simultaneous measurement of perfusion and oxygenation changes using a multiple gradient-echo sequence: application to human muscle study

We have developed a magnetic resonance imaging (MRI) technique based on a multiple gradient-echo sequence designed to probe perfusion and oxygenation simultaneously within skeletal muscle. Processing of the images acquired at successive echo times (TEs) generates two functional maps: one of the signal intensity (SI) extrapolated to zero echo time, which is sensitive to perfusion; and a second one of R2*, which reflects oxygenation. An advantage of the processing procedure lies in the selection of tissue of interest through the profile of T2* decay, leading to automatic rejection of pixels containing small vessels. This allows a more specific assessment of tissue perfusion and oxygenation. This technique was demonstrated successfully during post-ischemic reactive hyperemia in human calf. A perfusion peak of 123 mL x 100 g(-)1 x min(-1) was measured immediately after ischemia, whereas R2* value showed an 11.5% decrease at the same time, essentially reflecting blood oxygenation changes. Differences in the time courses of reperfusion and re-oxygenation were observed, oxygenation presenting a slower recovery. The mechanisms responsible for such a differential dynamic response are discussed.

13C/31P NMR studies of glucose transport in human skeletal muscle

The muscle intracellular (IC) free glucose concentration and the rate of muscle glycogen synthesis were measured by using in vivo 13C and 31P NMR spectroscopy in normal volunteers under hyperinsulinemic ( approximately 300 pM) clamp conditions at the following three plasma glucose levels: euglycemia ( approximately 6 mM), mild ( approximately 10 mM), and high ( approximately 16 mM) hyperglycemia. In keeping with biopsy studies, muscle IC free glucose concentration at euglycemia (-0.03 +/- 0.03 mmol/kg of muscle, mean +/- SEM, n = 10) was not statistically different from zero. A small but statistically significant amount of IC free glucose was observed during mild and high hyperglycemia: 0.15 +/- 0.08 (n = 5) and 0.43 +/- 0.20 mmol/kg of muscle (n = 5), respectively. Muscle glycogen synthesis rate, in mmol per kg of muscle per min, was 111 +/- 11 at euglycemia (n = 10), 263 +/- 29 during mild hyperglycemia (n = 5), and 338 +/- 42 during high hyperglycemia (n = 5), these three rates being significantly different from each other. As previous in vitro and in vivo studies, these rates suggest a Km (concentration at which unidirectional glucose transport reaches half-maximal rate) of the muscle glucose transport system in the 15-25 mM range under hyperinsulinemic conditions. The low concentrations of muscle IC free glucose observed under hyperinsulinemic conditions were interpreted, with this estimate and in the framework of metabolic control theory, as glucose transport being the predominant step controlling muscle glucose flux not only at euglycemia but also during hyperglycemia.

1H NMR spectroscopy study of the dynamic properties of glycogen in solution by steady-state magnetisation measurement with off-resonance irradiation

The dynamics of size-selected fractions of glycogen in solution have been investigated by proton NMR spectroscopy, using a recently described relaxation study method which relies on strong offresonance irradiation. The dependence of the steady-state magnetisation on angle and intensity of the effective radio-frequency field was measured and compared to theoretical curves derived from different models of motion. Absence or presence of contributions to relaxation from molecular motions on the microsecond time scale can be tested with this method, without having to resort to models. We found that glycogen dipolar relaxation did not result from isotropic Brownian rotation, and despite some contribution from slow motion (> 1 microsecond) to relaxation in glycogen alpha-particles extracted from rat liver, bulk movement of the molecules did not appear to participate in averaging the dipolar term to zero. Whereas hepatic glycogen rat beta-particles and commercial oyster glycogen displayed very similar relaxation properties, alpha-particles showed significantly different behaviour. However, all results were compatible with a diversity of movements within the molecule, ranging from freely rotating pyranoside rings through collective chain motion and possibly to bulk movement of the beta sub-units within the alpha-particle.

Low visibility of lactate in excised rat muscle using double quantum proton spectroscopy

Lactate NMR visibility was investigated in excised rat muscle at 3 T by comparing the concentration determined in situ by double quantum (DQ) proton spectroscopy (150 ms effective echo time) to the concentration measured in vitro from perchloric acid extracts of the same muscle samples. After 1-2 h of ischemia, lactate NMR visibility was 32 +/- 3% (+/- SE, n = 9), and was only 21 +/- 1% (n = 6) after 10-12 h. Muscle lactate T2 was 140 +/- 11 ms and 184 +/- 6 ms, respectively. All potential mechanisms of DQ lactate signal attenuation (B0 and B1 inhomogeneity, DQ transverse relaxation, diffusion) were examined, and accounted for when necessary. A significant increase in lactate NMR visibility was demonstrated using a shorter effective echo time (79 ms) DQ editing sequence. These results are interpreted as reflecting muscle lactate compartmentation between a long T2 pool predominantly detected by DQ spectroscopy, and a short T2 pool virtually invisible with longer echo time NMR techniques.

Simultaneous determination of muscle perfusion and oxygenation by interleaved NMR plethysmography and deoxymyoglobin spectroscopy

A novel approach is presented that combines NMR-plethysmography and NMRS of deoxymyoglobin in real-time, using line-by-line interleaved acquisitions of both gradient echo images during venous occlusion and of the N-delta proton signal of myoglobin's proximal F8 histidine. This method allowed simultaneous measurement of peripheral regional perfusion and skeletal muscle oxygen content. During reactive hyperaemia, using our combined NMRI-NMRS protocol, we explored the relationship between muscle reoxygenation (myoglobin resaturation half-time, y in s) and reperfusion (x in ml/100 g tissue/min) and found it to be highly significant (y = 70.83x-0.94; r2 = 0.70; F = 64.40; p = 9.73 x 10(-9). We also demonstrated that at low flow, muscle perfusion was a rate-limiting factor to reoxygenation. Making certain hypotheses, muscle oxygen extraction was derived from perfusion and myoglobin resaturation rate. Muscle oxygen extraction during early post-ischemic recovery (0.78 +/- 0.11, 0.79 +/- 0.09 and 0.72 +/- 0.05 at 0, 60 and 100 Torr counter-pressure, respectively) was shown to be independent of perfusion and maximum at each step of the protocol in most volunteers but also to display significant variability among subjects in this supposedly normal population sample.

An interleaved heteronuclear NMRI-NMRS approach to non-invasive investigation of exercising human skeletal muscle

Novel tools are presented that aim at more comprehensive NMR investigations of human skeletal muscle metabolism, in particular during exercise protocols. They integrate imaging (NMRI) and spectroscopy (NMRS) experiments in a single dynamic examination. The first sequence that we propose combine NMR-plethysmography, 1H-NMRS of deoxymyoglobin and 31P-NMRS. This allows simultaneous determination of skeletal muscle perfusion, oxygenation and high-energy phosphates status. It is very well suited to the study of interplay between blood supply and energy metabolism during the recovery period from aerobic or anaerobic exercise. In a second sequence, the same spectroscopic measurements are associated to a 1H double quantum coherence (DQC) edition of lactate. It is, this time, possible to estimate muscle lactate production concurrently with oxygen content, high-energy phosphates distribution and intracellular pH. This sequence is intended mainly for metabolic investigations of ischemic bouts. Examples are given of the use of these sequences in normal adult volunteers. They demonstrate the technical feasibility of these new approaches and illustrate their potential for future applications, particularly non-invasive of regulatory mechanisms of muscle metabolism in situ.

Evidence for 100% 13C NMR visibility of glucose in human skeletal muscle

The accuracy of the measurement of total muscle glucose by in vivo 13C NMR spectroscopy was tested in five normal volunteers during a euglycemic [1-13C]glucose infusion. The NMR visible concentration calibrated using an external reference was compared with that calculated from plasma glucose concentration, assuming that glucose remained extracellular. The NMR measurement always provided higher values than the calculation from plasma glucose: 0.51 +/- 0.035 (mean +/- SE) versus 0.38 +/- 0.005 mmol/liter of muscle on average. This systematic difference was interpreted as reflecting the presence of muscle glucose-6-phosphate, co-resonating with free glucose. Thus, glucose appeared to be virtually 100% NMR visible in human skeletal muscle.

In vivo NMR evidence for moderate glucose accumulation in human skeletal muscle during hyperglycemia

Although the absence of intracellular (IC) free glucose is direct evidence of glucose transport being the rate-limiting step for muscle glucose disposal at euglycemia, the scarcity of data in humans during hyperglycemia precludes any definitive conclusion. In the present study, 13C and 31P in vivo nuclear magnetic resonance (NMR) data from two separate groups of subjects were combined to measure IC free glucose in the human skeletal muscle. When these noninvasive tools were used with an infusion of [1-13C]glucose, a steady-state concentration of 1.2 +/- 0.2 mmol IC glucose/l IC water was observed at the end of a 2-h hyperglycemic clamp with somatostatin infusion, during which glycemia was maintained at approximately 22 mmol/l and insulinemia at approximately 5 mU/l. Despite this moderate glucose accumulation, the persistence of a large transmembrane glucose gradient suggests that the posttransport steps do not play a significant role in the control of muscle glucose disposal in these specific conditions, relevant to insulinopenic diabetic patients.

Practical implementation of single-voxel double-quantum editing on a whole-body NMR spectrometer: localized monitoring of lactate in the human leg during and after exercise

The classical double-quantum editing sequence 90 degrees,x-tau-180 degrees y-tau-90 degrees x-t1-90 degrees x-tau-180 degrees y-tau-AQ (tau = 1/4J) was rendered volume selective, by making slice selective the first 90 degrees pulse and the two 180 degrees pulses. Using simple rules to ensure optimum radio frequency phase coherence, this single-voxel editing sequence, reminiscent of a basic PRESS localization technique, was implemented on a whole-body 3 T spectrometer, and in vitro editing of lactate methyl protons was demonstrated without any significant loss in intrinsic sensitivity. The effectiveness of the proposed approach in vivo was also illustrated through the localized monitoring of lactate in the human leg during and after exercise.

C13 NMR spectroscopy of lipids: a simple method for absolute quantitation

There is both epidemiological and experimental evidence of the effect of fatty acid molecular structure, particularly the degree of saturation in fatty acyl chains, on the growth and regulation of certain tumours. In vivo carbon nuclear magnetic resonance spectroscopy has previously been shown to offer a non invasive technique for the evaluation of proportions of monounsaturated, polyunsaturated and saturated fatty acids in human adipose tissue. We present a simple method, which uses both endogenous water and fat as reference, to quantify in molar terms these lipid sub-categories for tissues other than pure fat. This could provide additional information in the debate on the protective effect in cancer of high polyunsaturated fatty acid (PUFA) diet. The method was validated by characterization of a lipid emulsion of known composition in various experimental set-ups and was applied to measure the lipid composition of the calves of two volunteers. Limitations and perspectives of the method are discussed.

1H NMR determination of lactate 13C-enrichment in skeletal muscle: using a double quantum filter for the simultaneous editing of 13C-coupled and 13C-uncoupled methyl protons resonance

1H NMR simultaneous editing of 13C-coupled and 13C-uncoupled methyl protons resonance, using the selection of double quantum coherences by a gradient pulse, was analyzed in vitro and demonstrated in situ on the hindlimb of an exercised rat model postmortem. In vitro calibration showed agreement with theoretical analysis. High-resolution NMR of muscle extract confirmed the accuracy of the lactate 13C-enrichment calculated using the in situ NMR data and the calibration factor obtained in vitro.

In vivo 31P nuclear magnetic resonance spectroscopy of skeletal muscle energetics in endotoxemic rats: a prospective, randomized study

OBJECTIVE

To identify possible alterations in the skeletal muscle high-energy phosphate metabolism at the early phase of endotoxic shock in rats.

DESIGN

A prospective, randomized study of skeletal muscle energetics in endotoxemic and in control rats, by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy at rest, under regional ischemia, and during reperfusion.

SETTING

Biochemical NMR laboratory equipped for surgery and hemodynamic monitoring.

SUBJECTS

Wistar rats were randomized to different groups. Eight rats were injected with Escherichia coli endotoxin (15 mg/kg, survival time 19 +/- 4 hrs) intraperitoneally. Seven other rats served as controls. The additional nine rats were studied for the saturation recovery pulse sequence.

INTERVENTIONS

In the treatment group, endotoxin was injected 8 hrs before NMR spectroscopy. The right hind limbs were studied under anaesthesia using a surface coil NMR probe. Their high-energy phosphate contents and intracellular pH were determined by 31P NMR spectroscopy. After baseline measurements, an ischemia-reperfusion challenge was imposed on the muscle by transient clamping of the abdominal aorta. Contralateral femoral artery pressure was constantly monitored.

MEASUREMENTS AND MAIN RESULTS

During the baseline period, the endotoxin-treated muscles did not show any difference in the distribution of the high-energy phosphate compounds or in intracellular pH, as compared with the controls. Ischemia resulted in a significantly faster decline of the inorganic phosphate/creatine phosphate ratio in the endotoxin-treated rats (1.35 +/- 0.17 vs. 0.51 +/- 0.06 at the end of the 38-min ischemic period). Skeletal muscle acidosis developed earlier and was deeper in the endotoxemic animals (pH: 6.94 +/- 0.02 vs. 7.02 +/- 0.03 at the end of ischemia). During reperfusion, the calculated time constants of recovery of inorganic phosphate to phosphocreatine ratios were identical between groups.

CONCLUSIONS

Resting nonischemic muscles of endotoxin-treated rats show no evidence of alterations in high-energy phosphate metabolism. However, under ischemic conditions, high-energy phosphate metabolism deteriorates faster in the skeletal muscles of treated animals. These data support the hypothesis of a greater mismatch during perfusion at very low pressure between residual oxygen availability and oxygen needs in the endotoxin-treated muscle cell.

The effect of technical conditions and storage medium composition on the phosphomonoesters to inorganic phosphate ratio determined by 31P nuclear magnetic resonance spectroscopy in rabbit kidney

Using 31P nuclear magnetic resonance spectroscopy, we compared the state of the high-energy phosphates in rabbit kidneys stored at 4 degrees C for 24 hr with 3 different solutions: Ringer (Rg), University of Wisconsin (UW), and Euro-Collins (EC) solutions. We found the highest phosphomonoester/inorganic phosphate (MP:Pi) ratio in the group of kidneys stored in the Rg solution (Rg, 0.93 +/- 0.04; UW, 0.36 +/- 0.02; EC, 0.28 +/- 0.02). This medium has been demonstrated in previous physiological studies to give poor results in terms of organ preservation compared to the solutions that mimic the "intracellular" fluid, such as the EC and UW solutions. Because the commonly used cold storage solutions contain phosphates, which superimpose on the intracellular Pi and, thus, can distort the results, we attempted to eliminate the contaminating solution around the kidney and in the vasculature by flushing the kidney with a phosphate-free solution (Rg). The MP:Pi ratio increased in the UW and EC groups (UW, 0.82 +/- 0.04; EC, 0.64 +/- 0.04) in identical proportion in the 2 groups. It remained highest in the Rg group (1.02 +/- 0.03). Comparisons of data before and after flush showed that external phosphate contamination was not predominant. There was no equilibrium in phosphate distribution between intra- and extracellular spaces at 24 hr of storage. We conclude that the validity of the MP:Pi ratio, as a viability index of renal transplant, might have to be restricted to comparisons of kidneys preserved in the same storage conditions. Therefore, it would be necessary to establish normal and pathological values of this ratio for each cold storage solution.

Effect of oral contraception on water-suppressed proton NMR spectra of plasma

Lipid linewidths were measured in the plasma proton spectra of young women. The individuals taking a contraceptive pill associating ethinyloestradiol and levonorgestrel or norethisterone were found with an average linewidth 2.5 Hz narrower than controls. As this drug regimen systematically induces an increase in plasma VLDL and a decrease in HDL/LDL ratio, our observation supports the theory that the Fossel test reflects plasma lipids abnormalities in cancer patients.

Myocardial protection during ischemia by prior feeding with the creatine analog: cyclocreatine

The ability of 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine), a synthetic creatine analog, to protect myocardium during global ischemia was assessed in isovolumic rat hearts using phosphorus-31 nuclear magnetic resonance spectroscopy. Wistar rats were fed a 1% cyclocreatine diet. After 2 weeks, cyclocreatine-fed (n = 8) and control (n = 7) rats were anesthetized, the heart was excised and retrograde perfusion was begun at 10 ml/min per g with 37 degrees C, phosphate-free buffer containing glucose and oxygen. Hemodynamic and spectroscopic data were obtained during baseline, ischemia and recovery periods (each 24 min). During ischemia, the heart of control rats developed a rigor-like increase in tonic pressure (ischemic contracture) not seen in the heart of cyclocreatine-fed rats (22 versus 1 mm Hg, p less than 0.01). This change was associated with significantly more adenosine triphosphate (ATP) at end-ischemia in the cyclocreatine group (1.6 versus 0.6 mumol/g, p less than 0.01) and delayed development of acidosis (p less than 0.001). With reperfusion, the heart of cyclocreatine-fed rats spontaneously defibrillated sooner than did the heart in control rats (178 versus 346 s, p less than 0.03). Diastolic pressure remained significantly elevated throughout recovery in control hearts compared with treated hearts (p less than 0.001). Prior feeding with cyclocreatine preserves myocardial adenosine triphosphate during ischemia, delays the development of acidosis and ischemic contracture and improves recovery of mechanical function on reperfusion.

Cardiovascular structural changes induced by isolation-stress hypertension in the rat

The cardiovascular structural remodelling associated with psychogenic hypertension was investigated in genetically normotensive rats subjected to isolation stress. Male Wistar rats were stressed by intermittent social isolation and compared to control rats living in groups. The stressed rats had higher systolic blood pressures than the control rats throughout the study. After 1 week of isolation, ornithine decarboxylase activity, a marker for hypertrophy, was increased in the right ventricle of the stressed rats. After 6 weeks of intermittent isolation, the myocardium of the stressed rats was hypertrophied, involving both right and left ventricles. The aorta was also hypertrophied, whereas the tail artery remained unaffected. Later, after 12 weeks of isolation, the left ventricular hypertrophy persisted whereas the right ventricle and aorta returned to normal. It seems, therefore, that social stress hypertension is accompanied by very early structural changes, which affect at least the heart and the aorta, and cannot be directly linked to the severity or duration of hypertension.

[Does ambulatory blood pressure measurement allow a better definition of arterial hypertension?]

The lack of effect of treatment of mild hypertension on the coronary heart disease has motivated researches for a better diagnosis of hypertension. One of the approaches presently under study uses the recording of ambulatory blood pressure using semi-automatic devices. The usefulness of these apparatus is however restricted by the lack of reference values recorded in normotensive control patients. We have recorded ambulatory blood pressure (PAA) in 24 normotensives, 22 untreated hypertensives and 45 treated hypertensive patients, and compared the data obtained to the blood pressure recorded during medical examination (PAC). If a good correlation is usually observed between PAA and PAC, very large and unpredictable discordances are frequently observed. No correlation is found between the difference PAA-PAC and the variability of PAA. This variability does not fully explain the difference observed between PAA and PAC. This variability expressed in mmHg increases with age and the level of BP. Ambulatory BP appears to be a very reproducible value which may allow to improve the definition of hypertension and there-fore the cardiovascular risk.

Interrelationship of hypertension, plasma lipids and atherosclerosis

The relationship between hypertension and atherosclerosis has been illustrated by epidemiological, clinical and experimental observations. Typical atherosclerotic lesions develop in arterial wall when hypercholesterolaemia is present. Hypertension aggravates these lesions by causing vascular structural changes. In clinical studies, however, the correction of high blood pressure does not decrease the incidence of coronary heart disease. Several hypotheses have been formulated to account for this observation: one is that reversibility of the structural vascular changes induced by hypertension is not complete when the blood pressure is lowered; another is that antihypertensive drugs have a deleterious effect on the vascular wall.

Alterations of intestinal membrane-bound enzymes in three types of hypertensive rats

Alkaline phosphatase, sucrase, Na+,K+-ATPase and Mg2+-ATPase specific activities of crude membrane fractions, prepared from duodenal, jejunal, ileal and colonic mucosa, have been estimated in three types of hypertensive rats: the spontaneously hypertensive rat (SHR), the DOCA-saline treated rat and the renovascular rat (Goldblatt one-kidney, one-clip rat; 1K-1C). Alkaline phosphatase and sucrase specific activities have been measured in purified jejunal brush-border membranes. When compared with its normotensive age-matched control (WKY rat), the SHR has a lower activity of alkaline phosphatase in duodenal and jejunal crude membrane fractions, whereas a higher activity in colonic Na+,K+-ATPase is recorded. In purified jejunal brush-border membranes, lower alkaline phosphatase activity and higher sucrase activity were found. These differences occur in the young prehypertensive SHR as well as in the adult animal. In the DOCA-treated rat, the only significant alteration in crude membrane fractions is a decreased Mg2+-ATPase activity at all regions of intestinal mucosa. In purified jejunal brush-border membranes both alkaline phosphatase and sucrase activities are increased at 4 or 7 weeks but especially at 13 weeks of hypertension. In the 1K-1C rat, no significant modification appears in crude membrane fractions or in purified jejunal brush-border membranes, but a decrease in alkaline phosphatase and in sucrase activities is probable after 13 weeks of hypertension. Since alterations of the intestinal enzymes are different in the three types of hypertensive rats it is concluded that the changes are not secondary to the hypertension condition. In the SHR, these alterations are present in the young prehypertensive animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial metabolism as studied in vitro by NMR: preliminary results in normotensive and hypertensive aortas

Arterial tissue has been analysed by 31P-, 13C-, 23Na- and 1H-NMR spectroscopy. Rabbit thoracic aortas were mounted on a system with perfusate circulation and studied in basal conditions. Phosphorus spectra remained stable for hours and showed low levels of phosphocreatine (PCr) compared to skeletal, cardiac or even to nonvascular smooth muscle. Significant levels of sugar-phosphates (SP), phosphodiesters (PDE) were detected, as well as occasionnally a peak in the diphosphodiester region. Experiments with phosphate-free perfusate demonstrated a very low level of intracellular inorganic phosphate. As expected from previous data, free ADP levels in tonic arterial tissue were found much higher than in any other muscle. Addition of norepinephrine into the perfusate induced transient decrease in ATP and PCr levels, associated with an increased production of phosphorylated intermediates. At the early stage of renovascular hypertension, aortic energetic pattern was characterized by an increased ADP/ATP ratio. Natural abundant 13C spectra were recorded from dog aortic fragments and showed mainly resonances attributed to fatty components. After addition of a shift-reagent, dysprosium tripolyphosphate, 23Na-NMR allowed separation of intra- and extracellular Na of perfused rabbits aortas. Proton NMR of lyophilized aortic fragments revealed several peaks originating from biologically relevant molecules, lactate, creatine, taurine... These preliminary data demonstrate the feasability of multinuclear NMR spectroscopy of vascular tissue and are suggestive of the potential of the method when it will be combined with monitoring of functional parameters.

Vasopressin as a putative mediator in SHR hypoalgesia

The purpose of this note is to show that vasopressin might be involved in the hypoalgesia of the spontaneously hypertensive rat. This proposal rests upon published data.

Kinetics of proliferation of rat aortic smooth muscle cells in Goldblatt one-kidney, one-clip hypertension

Wistar female rats were made hypertensive by applying a silver clip to the left renal artery and removing the right kidney. In aortas, the proliferation fraction of smooth muscle cells, DNA synthesis and wet weight have been correlated with the blood pressure increase subsequent to the operation. A wave of proliferation of smooth muscle cells in the aortic media is triggered immediately after the highest increased rate of blood pressure. When blood pressure stabilizes at high values, the metabolism of nucleic acid within the aortic media resumes its normal level but the arterial changes previously established persist. The sequence of pathological events responsible for these changes could be: increment of blood pressure; increase in wall stress; proliferation of smooth muscle cells; thickening of arterial wall; correction of the wall stress; end of proliferation. The consequence of this early proliferation of aortic smooth muscle cells is not clear but it is probably one of the mechanisms through which high blood pressure is sustained. It can also participate in atherogenesis, being in this way one of the bases of the well-known relationship between hypertension and atherosclerosis.

Evolution of aortic hyperplasia after reversal of renovascular hypertension in the rat

Unclipping of Goldblatt one-kidney, one clip hypertensive rats leads to a rapid correction of the high blood pressure. Simultaneously, the aortic smooth muscle cell proliferation wave is stopped. Any further proliferation is prevented but the proliferation changes previously established cannot be reversed. Thus, provided clip removal is performed at the earliest phase of hypertension, it can modify the time-course of the aortic proliferation changes. On the contrary, the heart hypertrophy is significantly improved regardless of the unclipping time. Accordingly, the response of the hypertensive cardiovascular modifications to an antihypertensive therapy cannot be regarded as a whole since it is dependent on the cardiovascular target as well as on the onset time of treatment.