Bioenergetic remodeling of heart during treatment of spontaneously hypertensive rats with enalapril

We used spontaneously hypertensive rats to study remodeling of cardiac bioenergetics associated with changes in blood pressure. Blood pressure was manipulated with aggressive antihypertensive treatment combining low dietary salt and the angiotensin-converting enzyme inhibitor enalapril. Successive cycles of 2 wk on, 2 wk off treatment led to rapid, reversible changes in left ventricular (LV) mass (30% change in <10 days). Despite changes in LV mass, specific activities of bioenergetic (cytochrome-c oxidase, citrate synthase, lactate dehydrogenase) and reactive oxygen species (ROS) (total cellular superoxide dismutase) enzymes were actively maintained within relatively narrow ranges regardless of treatment duration, organismal age, or transmural region. Although enalapril led to parallel declines in mitochondrial enzyme content and ventricular mass, total ventricular mtDNA content was unaffected. Altered enzymatic content occurred without significant changes in relevant mRNA and protein levels. Transcript levels of gene products involved in mtDNA maintenance (Tfam), mitochondrial protein degradation (LON protease), fusion (fuzzy onion homolog), and fission (dynamin-like protein, synaptojanin-2alpha) were also unchanged. In contrast, enalapril-mediated ventricular and mitochondrial remodeling was accompanied by a twofold increase in specific activity of catalase, an indicator of oxidative stress, suggesting that rapid cardiac adaptation is accompanied by tight regulation of mitochondrial enzyme activities and increased ROS production.

Recovery of erectile function after brief aggressive antihypertensive therapy

PURPOSE

We have previously demonstrated that antihypertensive therapy could structurally modulate blood vessels in the penis, although the impact on erectile function was not established. Given the importance of inadequate penile arterial inflow as a cause of erectile dysfunction we determined in spontaneously hypertensive rats the impact of brief aggressive antihypertensive therapy on structurally based penile vascular resistance, erectile function and mean arterial pressure during and after treatment.

MATERIALS AND METHODS

Young (15-week-old) and aged (40-week-old) spontaneously hypertensive rats were treated for 2 weeks (enalapril 30 mg./kg. daily plus a low salt diet). Mean arterial pressure was continuously monitored via radio telemetry. Erectile responses were assessed by administering apomorphine (80 microg./kg. subcutaneously) before, during and after treatment. Structurally based vascular resistance was determined in the isolated, perfused penile vasculature 2 weeks after stopping treatment in aged spontaneously hypertensive rats. Certain responses were determined, including resistance at maximum dilatation (lumen size) and at maximum constriction (medial bulk), and EC50 of the alpha-adrenoceptor agonist methoxamine.

RESULTS

In the period after the cessation of drug treatment there was a persistent reduction in the level of arterial pressure (16%) and a doubling of erectile responses compared with pre- treatment. Cardiac and vascular structure regressed, as determined by the mean decrease plus or minus standard deviation in vascular resistance at maximum dilatation (21% +/- 4.5%) and mean reduction in left ventricle mass (10.4% +/- 3.7%). Furthermore, treatment induced a significant right shift in alpha1-adrenoceptor concentration response curve in treated versus control rats (mean EC50 1.09 +/- 0.111 versus 0.76 +/- 0.111).

CONCLUSIONS

The improvement in erectile function after brief aggressive treatment may be related to improvement in structurally based vascular resistance within the penis and the decrease in responsiveness of alpha1-adrenoceptor mediated erectolytic signaling. These findings are suggestive of a new therapeutic strategy for hypertension and erectile dysfunction.

Development of a rat model of sexual performance anxiety: effect of behavioural and pharmacological hyperadrenergic stimulation on APO-induced erections

As part of the multifactorial nature of erectile dysfunction, anxiety associated with sexual performance (SPA) remains a major contributing factor to its progression. In fact, the heightened sympathetic activity associated with sexual performance anxiety may be a key early component of this disruption of normal erectile responses. We are not aware that any animal models have been developed to assess this phenomenon. Using apomorphine (APO, 80 microg/kg s.c.)-induced erections in rats we characterised the effects of behavioural or pharmacological hyperadrenergic stimulation (that is, anxiety) on erections and hemodynamics. We developed an experimental SPA paradigm by exposing male rats to the stress of being observed by a larger, older male rat placed in close proximity to test rats during APO testing. In a separate group, adrenergic stress was simulated using a sympathomimetic, methoxamine (MXA) given prior to APO testing. In a third group, the changes in circulatory parameters (mean arterial pressure, heart rate) were determined following instrumentation with radiotelemetric transducers for each scenario. APO-induced erections were significantly lower in both the behavioural (1.25+/-0.8) and pharmacological (0.33+/-0.5) stressor paradigms compared to controls (2.81+/-0.9). Further, erections in MXA-treated rats were significantly lower than in the observed scenario. Despite the differences in erections hemodynamic assessments showed no differences in MAP or HR changes between the different experimental conditions. Thus, both the behavioural and pharmacological paradigms of SPA decreased erections, but did not affect the circulation. This suggests that the level of hyperadrenergic input required to induce erectile dysfunction can be subtle, and target only erectogenic pathways.

Nitric oxide-mediated regulation of chemosensitivity in cancer cells

BACKGROUND

Hypoxia in tumors is associated with malignant progression, metastatic spread, and increased resistance to radiotherapy and chemotherapy. Molecular O(2) is required for the cellular production of nitric oxide (NO) by the enzyme NO synthase (NOS), and NO may block components of the adaptive response to hypoxia. Hence, we hypothesized that hypoxia increases drug resistance in tumor cells by inhibiting endogenous NO production.

METHODS

Human breast carcinoma (MDA-MB-231) and mouse melanoma (B16F10) cells were pre-exposed to 20% O(2), 5% O(2), or 1% O(2), incubated with a pharmacologic inhibitor of endogenous NO production, and then treated with chemotherapeutic agents. Resistance was assessed by colony-formation assays, and western blot analysis was used to measure NOS protein levels. All P values were two-sided.

RESULTS

Incubation of MDA-MB-231 tumor cells in 1% O(2) maximally increased their resistance to doxorubicin and 5-fluorouracil by 8.5-fold (P =.002) and 2.3-fold (P =.002), respectively, compared with incubation in 20% O(2). B16F10 mouse melanoma cells preincubated in 1% O(2) (versus 20% O(2)) for 12 hours exhibited a twofold increase in resistance to doxorubicin (P<.001). The rapid acquisition of drug resistance after exposure to 1% O(2) could be mimicked by incubating the MDA-MB-231 cells for 12 hours with the NOS inhibitor N(G)-monomethyl-Larginine (fivefold increase; P<.001). Conversely, replacement of NO activity by use of the NO-mimetic glyceryl trinitrate (GTN) and diethylenetriamine NO adduct produced statistically significant attenuations in the development of resistance of 59% (P<.001) and 40% (P<.001), respectively, in MDA-MB-231 cells. Treatment of B16F10 cells with GTN produced a 58% reduction in resistance (P<.001). MDA-MB-231 cells expressed all three isoforms of the NOS enzyme at levels that were not altered by exposure to hypoxia.

CONCLUSIONS

NO mediates chemosensitivity in tumor cells, and hypoxia-induced drug resistance appears to result, in part, from downstream suppression of endogenous NO production. These results raise the possibility that administration of small doses of NO mimetics could be used as an adjuvant in chemotherapy.

An EMG technique for measuring spinal loading during asymmetric lifting

OBJECTIVES

To compare two methods of calibrating the erector spinae electromyographic signal against moment generation in order to predict extensor moments during asymmetric lifting tasks, and to compare the predicted moments with those obtained using a linked-segment model.

METHODS

Eight men lifted loads of 6.7 and 15.7 kg at two speeds, in varying amounts of trunk rotation. For each lift, the following were recorded at 60 Hz; the rectified and averaged surface electromyographic signal, bilaterally at T10 and L3, lumbar curvature using the 3-Space Isotrak, movement of body segments using a 4-camera Vicon system, and ground reaction forces using a Kistler force-plate. Electromyographic (EMG) and Isotrak data were used to calculate lumbosacral extensor moments using the electromyographic model, whereas movement analysis data and ground reaction forces were used to estimate net moments using the linked-segment model. For the electromyographic technique, predictions of extensor moment were based on two different sets of EMG-extensor moment calibrations: one performed in pure sagittal flexion and the other in flexion combined with 45 degrees of trunk rotation.

RESULTS

Extensor moments predicted by the electromyographic technique increased significantly with load and speed of lifting but were not influenced by the method of calibration. These moments were 7-40%greater than the net moments obtained with the linked-segment model, the difference increasing with load and speed.

CONCLUSIONS

The calibration method does not influence extensor moments predicted by the electromyographic technique in asymmetric lifting, suggesting that simple, sagittal-plane calibrations are adequate for this purpose. Differences in predicted moments between the electromyographic technique and linked-segment model may be partly due to different anthropometric assumptions and different amounts of smoothing and filtering in the two models, and partly due to antagonistic muscle forces, the effects of which cannot be measured by linked-segment models. RelevanceAsymmetric lifting is a significant risk factor for occupationally-related low back pain. Improved techniques for measuring spinal loading during such complex lifting tasks may help to identify work practices which place the spine at risk of injury.

Recent advances in lumbar spinal mechanics and their significance for modelling

Mathematical models are often used to quantify the overall forces and moments acting on the lumbar spine. However, if the purpose of the research is to explain how spinal tissues can be injured, it is necessary to distribute the overall forces and moments between (and within) different spinal structures, because it is the concentration of force which causes injury, and elicits pain. This paper reviews recent experimental evidence concerning the distribution of forces and moments acting on the lumbar spine. Lordotic postures increase loading of the posterior annulus and apophyseal joints, whereas moderately flexed postures tend to equalise compressive stress across the disc, and unload the apophyseal joints. Sustained compression reduces the volume and pressure of the nucleus pulposus, while increasing compressive stresses in the annulus and neural arch. Sustained compression also reduces disc height, giving some slack to collagen fibres in the intervertebral disc and ligaments, and causing them to resist bending less. Disc degeneration has a similar effect on disc height, and stress distributions. On the other hand, discs and ligaments can be subjected to greater bending moments following a period of sustained or repetitive bending, because sustained bending impairs the normal protective reflex from the back muscles, and repetitive bending fatigues the back muscles, reducing their ability to protect the spine. Incorporating this information into mathematical models will make them better able to identify which activities are most likely to injure the lumbar spine in life.

Lumbar loading during lifting: a comparative study of three measurement techniques

Low back loading during occupational lifting is thought to be an important causative factor in the development of low back pain. In order to regulate spinal loading in the workplace, it is necessary to measure it accurately. Various methods have been developed to do this, but each has its own limitations, and none can be considered a "gold standard". The purpose of the current study was to compare the results of three contrasting techniques in order to gain insight into possible sources of error to which each is susceptible. The three techniques were a linked segment model (LSM), an electromyographic (EMG)-based model, and a neural network (NN) that used both EMG and inertial sensing techniques. All three techniques were applied simultaneously to calculate spinal loading when eight volunteers performed a total of eight lifts in a laboratory setting. Averaged results showed that, in comparison with the LSM, the EMG technique calculated a 25.5+/-33.4% higher peak torque and the NN technique a 17.3+/-10.5% lower peak torque. Differences between the techniques varied with lifting speed and method of lifting, and could be attributed to differences in anthropometric assumptions, antagonistic muscle activity, damping of transient force peaks by body tissues, and, specific to the NN, underestimation of trunk flexion. The results of the current study urge to reconsider the validity of other models by independent comparisons.

Antihypertensive drugs induce structural remodeling of the penile vasculature

PURPOSE

There is a strong association between hypertension and erectile dysfunction. Studies of the treatment of hypertension have shown that some pharmacological agents are capable of inducing regression of the vascular structure during treatment. We determined whether penile vascular structure is as susceptible as other vascular beds to regression during antihypertensive drug treatment.

MATERIALS AND METHODS

Adult spontaneously hypertensive rats were treated for 1 or 2 weeks with 30 mg./kg. enalapril daily, or for 2 weeks with 45 mg./kg. hydralazine daily. Structurally based vascular resistance was determined in isolated penile and skeletal muscle vascular beds perfused with Tyrode-dextran. A cumulative alpha1-adrenoceptor concentration constrictor response curve to 1 to 100 microg./ml. methoxamine was constructed and the maximum constrictor response (vasopressin, methoxamine and angiotensin II) indicating the tissue yield point (that is the average medial bulk of vascular smooth muscle) was determined. The hearts were excised and the ventricles were separated and weighed.

RESULTS

Enalapril treatment progressively regressed cardiac and vascular structure during the 1 and 2-week treatment periods with a mean tissue yield point plus or minus standard deviation of -5.91% +/- 5.1% (p <0.05) and -12.1% +/- 6.0% (p <0.05), and a mean left ventricle mass of -11.8% +/- 2.2% (p <0.05) and -13.6% +/- 3.2% (p <0.05), respectively. Hydralazine treatment for 2 weeks was less effective on vascular regression with a mean yield of -7.3% +/- 2.9% (p <0.05) and it did not alter left ventricle hypertrophy compared with controls (3.7% +/- 5.0%).

CONCLUSIONS

The data suggest that renin-angiotensin system inhibition may at least partially normalize penile vascular structure. The impact of these changes on erectile function must be determined.

How severe must repetitive loading be to kill chondrocytes in articular cartilage?

OBJECTIVE

Little is known about the effects of severe repetitive loading on articular cartilage chondrocytes, even though epidemiological studies associate this type of loading with osteoarthritis. We hypothesize that repetitive loading can kill cartilage chondrocytes in a dose-related manner.

DESIGN

Large cartilage-on-bone specimens were cut from the patella groove of bovine knees obtained directly from a slaughterhouse. Cartilage was loaded using a flat impermeable indenter in such a manner that the loaded region was supported naturally by surrounding cartilage and subchondral bone. Specimens received 3600 cycles of compressive loading at 1 Hz, with the peak load lying in the range 1-70% of the force required to damage cartilage in a single loading cycle (35 MPa). Cell viability was assessed in thick sections of loaded and control cartilage using a paravital staining method: fluorescein diacetate stained live cells green, and propidium iodide stained dead cells red. The assay was validated on cartilage which had been subjected to repeated freeze-thaw cycles to kill the chondrocytes.

RESULTS

Paravital staining revealed 100% cell death after one freeze-thaw cycle at -196 degrees C and three cycles at -20 degrees C. Baseline chondrocyte viability was 80% in unloaded cartilage, and viability decreased when applied compressive loading exceeded 6 MPa. Above this threshold, cell viability was inversely proportional to applied stress. When gross damage to the cartilage surface first became evident, above 14 MPa, 40% of cells remained viable. Load-induced chondrocyte death was greatest in the surface zone, and extended beyond the loaded area. Electron micrographs indicated that some cells were dying by apoptosis.

CONCLUSIONS

Some chondrocytes are much more vulnerable to repetitive mechanical loading than others, suggesting that vigorous activity may lead to cell death in articular cartilage.

Telemetric blood pressure monitoring in conscious rats before and after compression injury of spinal cord

Abnormal cardiovascular control after spinal cord injury (SCI) results in hypotension soon after injury. Later, paroxysmal hypertension and bradycardia in response to sensory stimulation below the level of injury develop in most people with SCI. In this study, we used a radiotelemetry system, in rats (n = 7), to investigate the effect of a clinically relevant compression model of SCI at T5 spinal segment on mean arterial pressure (MAP) and heart rate (HR) at rest and in response to colorectal distension. The transducers were implanted 1 month before clip compression (50-g) injury and continuous recording of MAP and HR was established for a period of 2.5 months. SCI was associated with hypotension (86+/-3 mm Hg) at 1 day after injury. In the following 2 days, MAP gradually returned to preinjury levels. By contrast, HR increased at 1 day after SCI and remained unchanged thereafter. Three days after SCI, colorectal distension caused an increase in MAP of 8+/-2 mm Hg accompanied by bradycardia (-18 bpm). One week after SCI, colorectal distension induced an increase in MAP of 9+/-2 mm Hg and bradycardia (-41 bpm). In the following days, the magnitude of reflex hypertension gradually increased, reaching 21+/-4 mm Hg at 1.5 months after SCI. In summary, our data show that resting MAP rapidly returns to control values after SCI. Episodic hypertension associated with autonomic dysreflexia can develop in rats within 1 month after incomplete SCI.

An improved heat pulse method to measure low and reverse rates of sap flow in woody plants

The compensation heat pulse method (CHPM) is of limited value for measuring low rates of sap flow in woody plants. Recent application of the CHPM to woody roots has further illustrated some of the constraints of this technique. Here we present an improved heat pulse method, termed the heat ratio method (HRM), to measure low and reverse rates of sap flow in woody plants. The HRM has several important advantages over the CHPM, including improved measurement range and resolution, protocols to correct for physical and thermal errors in sensor deployment, and a simple linear function to describe wound effects. We describe the theory and methodological protocols of the HRM, provide wound correction coefficients, and validate the reliability and accuracy of the technique against gravimetric measurements of transpiration.

Does nitric oxide play a role in the aetiology of pre-eclampsia?

Although progress has been made toward our understanding of the pathophysiology of pre-eclampsia, the precise aetiology of this disease still remains an enigma. One of the hallmarks of pre-eclampsia is a failure of the extravillous cytotrophoblast cells to invade and remodel the uterine spiral arterioles during the first trimester of pregnancy. Moreover, studies suggest that the cause of this disorder may be immunological in nature. Evidence is provided here suggesting that impaired trophoblastic invasion of the spiral arterioles may be linked to the altered immunological response associated with pre-eclampsia. Previous studies by Reister et al., 1999 demonstrated a direct relationship between macrophage infiltration of the myometrial segments of spiral arterioles and reduced trophoblastic invasion in pre-eclampsia. Also, it is well established that activated macrophages produce large amounts of nitric oxide (NO). Our present findings reveal that low concentrations of NO-mimetic drugs (glyceryl trinitrate and sodium nitroprusside) inhibit the ability of trophoblast cells to penetrate through reconstituted extracellular matrix (Matrigel). This inhibition is accompanied by a reduced expression of the cell surface urokinase receptor, a molecule important for invasion. These results suggest a possible mechanistic link between the aberrant macrophage infiltration associated with pre-eclampsia, and the maladapted uteroplacental arterioles that characterize the disease.

The feasibility and efficacy of tobacco use prevention in orthodontics

SMILES PLUS was the first study to extend the clinician-delivered logic model to prevention of tobacco use among adolescents. This multi-site trial with 154 participating offices, based on social learning theory and a behavioral ecological model, was designed to test whether orthodontists can prevent preteens from initiating smoking. The study found that orthodontists do not automatically adhere to anti-tobacco prevention services. Social learning variables can enhance both adherence to counseling guidelines and content of counseling to increase prevention effects. Providing financial incentives, tracking prescriptions, prompting positive feedback from patients, and adopting anti-tobacco counseling models in the office are likely to enhance anti-tobacco preventive services. Training orthodontists to be comfortable when advising nonsmoking youth not to start and to use social consequences to justify youth avoidance of tobacco might increase adherence to protocols and make their counseling more powerful. Adolescent smokers prior to intervention were more likely to start other risky behaviors later. Preventing tobacco use may halt additional risk behaviors and thereby reduce morbidity/mortality even more than expected from tobacco control alone. New and refined clinical trials should be conducted to determine the most effective interventions for adolescent tobacco control by clinicians.

Sustained loading increases the compressive strength of articular cartilage

INTRODUCTION

When synovial joints are subjected to sustained or repetitive loading, fluid is driven from the articular cartilage so that it is less able to equalise compressive stress between opposing joint surfaces. We test the hypothesis that sustained loading reduces the compressive strength of cartilage-on-bone.

METHODS

Forty specimens of articular cartilage-on-bone, approximately 15 mm square, were removed from the patella groove of mature bovine knees. Specimens were loaded on a materials testing machine using a 5 mm-diameter plane-ended indentor. Controlled loading/unloading cycles of 1s duration, and of increasing severity, were applied until failure was evident on the force-deformation graphs. Half of the specimens were 'creep loaded' for 30 at 2 MPa before their strength was assessed. After testing, damage was investigate using ink staining of the cartilage surface, and histology.

RESULTS

Sustained loading reduced cartilage thickness by 45% and creep-loaded specimens were 21% stronger (P = 0.01). Most specimens appeared to fail by fissuring of the cartilage surface zone.

CONCLUSION

Sustained loading strengthens cartilage by expelling water from it, reducing the tendency of the surface zone to rupture in the manner of an over-inflated car tyre.

Endothelin receptor antagonism does not prevent the development of in vivo glyceryl trinitrate tolerance in the rat

There is evidence that increased endothelial production of endothelin-1 (ET-1) may contribute to glyceryl trinitrate (GTN) tolerance. We used the competitive ET(A) receptor antagonist ZD2574 to determine whether chronic ET(A) receptor blockade affected the biochemical and functional responses to GTN during the development of GTN tolerance in vivo. Tolerance induced using transdermal GTN patches resulted in a 5.3 +/- 1.2-fold increase in the EC(50) value for GTN relaxation in isolated aorta from GTN-tolerant rats. Coadministration of ZD2574 (100 mg kg(-1) t.i.d. for 3 days) during tolerance induction had no effect on GTN-induced relaxation. This dose of ZD2574 markedly blunted the pressor response to ET-1, indicating effective blockade of ET(A) receptors, and also abolished the initial transient depressor response to ET-1, indicating that blockade of endothelial ET(B) receptors also occurred using this dosage regimen for ZD2574. Consistent with the relaxation data, coadministration of ZD2574 had no effect on the decrease in GTN-induced cGMP accumulation or on the decrease in GTN biotransformation that occurred in aortae from GTN-tolerant animals. Radioimmunoassay data indicated that the GTN tolerance induction protocol caused a 2.3 +/- 0.4-fold and a 2.2 +/- 0.5-fold increase in total tissue ET-1 levels in tolerant aorta and vena cava, respectively. These data suggest that chronic inhibition of ET receptors by ZD2574 was not sufficient to prevent or diminish the tolerance-inducing effects of GTN, and that the increase in ET-1 levels observed in tolerant tissues may occur as a consequence of the vascular changes that occur during chronic GTN exposure.

Hypoxia induces the expression of a 43-kDa protein (PROXY-1) in normal and malignant cells

This study was designed to determine the expression of cellular factors that may participate in phenotypic changes that occur under conditions of hypoxia. Using the RT-PCR differential display method, we isolated a cDNA fragment corresponding to a gene whose expression was induced in trophoblast and breast carcinoma cells cultured under 1 or 2% oxygen vs 4% oxygen or higher. This gene encodes a 43-kDa protein initially identified in homocysteine-treated endothelial cells and later shown to be upregulated in various human and mouse cell types (termed RTP, Drg1, Cap43, rit42, Ndr1). Herein we refer to this gene product as PROXY-1, for Protein Regulated by OXYgen-1. Elevated mRNA and protein levels were first observed in cells cultured in 1% oxygen for 8 h. Although PROXY-1 mRNA levels returned to near-control values within 2 h of reexposure to 20% oxygen, protein levels remained high 72 h after reexposure to 20% oxygen. Treatment of cells with hypoxia mimics such as cobalt or iron chelators also increased PROXY-1 expression. Moreover, presence of 30% carbon monoxide in the hypoxic atmosphere abrogated the upregulation of PROXY-1 expression. These findings suggest that hypoxia upregulates PROXY-1 levels through a heme protein-dependent pathway and that assessment of PROXY-1 expression may be of potential use in evaluating tissue hypoxia.

Trade-offs between the persistence of foliage and productivity in two Pinus species

We investigated interspecific variation in leaf lifespan (persistence) and consequent differences in leaf biochemistry, anatomy, morphology, patterns of whole-tree carbon allocation and stand productivity. We tested the hypothesis that a species with short-lived foliage, Pinus radiata D. Don (mean leaf lifespan 2.5 years), grows faster than P. pinaster Ait., a species with more persistent foliage (leaf lifespan 5.6 years), and that the faster growth rate of P. radiata is associated with a greater allocation of nitrogen and carbon to photosynthetic tissues across a range of scales. In fully sunlit foliage, the proportion of leaf N in the major photosynthetic enzyme Rubisco (ribulose-1, 5-bisphosphate carboxylase) was greater in P. radiata than in P. pinaster, and, in mid-canopy foliage, the proportion of leaf N in thylakoid proteins was greater in P. radiata. A lesser proportion of needle cross-sectional area was occupied by structural tissue in P. radiata compared to P. pinaster. Foliage mass in stands of P. radiata was 9.7 t ha^-1 compared with 18.2 t ha^-1 in P. pinaster while leaf area index of both species was similar at 4.6 m² m^-2, owing to the compensating effect of differences in specific leaf area. Hence trade-offs between persistence and productivity were apparent as interspecific differences in patterns of whole-tree carbon allocation, needle morphology, anatomy and biochemistry. However, these interspecific differences did not translate into differences at the stand scale since rates of biomass accumulation were similar in both species (P. radiata 6.9±0.9 kg year^-1 tree^-1; P. pinaster 7.4±0.9 kg year^-1 tree^-1). The similarities in performance at larger scales suggest that leaf area index (and radiation interception) determines growth and productivity.

Mechanical initiation of intervertebral disc degeneration

STUDY DESIGN

Mechanical testing of cadaveric lumbar motion segments.

OBJECTIVES

To test the hypothesis that minor damage to a vertebral body can lead to progressive disruption of the adjacent intervertebral disc.

SUMMARY OF BACKGROUND DATA

Disc degeneration involves gross structural disruption as well as cell-mediated changes in matrix composition, but there is little evidence concerning which comes first. Comparatively minor damage to a vertebral body is known to decompress the adjacent discs, and this may adversely affect both structure and cell function in the disc.

METHODS

In this study, 38 cadaveric lumbar motion segments (mean age, 51 years) were subjected to complex mechanical loading to simulate typical activities in vivo while the distribution of compressive stress in the disc matrix was measured using a pressure transducer mounted in a needle 1.3 mm in diameter. "Stress profiles" were repeated after a controlled compressive overload injury had reduced motion segment height by approximately 1%. Moderate repetitive loading, appropriate for the simulation of light manual labor, then was applied to the damaged specimens for approximately 4 hours, and stress profilometry was repeated a third time. Discs then were sectioned and photographed.

RESULTS

Endplate damage reduced pressure in the adjacent nucleus pulposus by 25% +/- 27% and generated peaks of compressive stress in the anulus, usually posteriorly to the nucleus. Discs 50 to 70 years of age were affected the most. Repetitive loading further decompressed the nucleus and intensified stress concentrations in the anulus, especially in simulated lordotic postures. Sagittal plane sections of 15 of the discs showed an inwardly collapsing anulus in 9 discs, extreme outward bulging of the anulus in 11 discs, and complete radial fissures in 2 discs, 1 of which allowed posterior migration of nucleus pulposus. Comparisons with the results from tissue culture experiments indicated that the observed changes in matrix compressive stress would inhibit disc cell metabolism throughout the disc, and could lead to progressive deterioration of the matrix.

CONCLUSIONS

Minor damage to a vertebral body endplate leads to progressive structural changes in the adjacent intervertebral discs.

Measurement of sap flow in roots of woody plants: a commentary

Measurements of sap flow in roots have recently been used to study patterns of resource acquisition by woody plants; however, the various thermometric methods employed have yielded disparate findings. These findings may be harmonized by accounting for the phenomenon of reverse sap flow in roots. We suggest that only methods capable of measuring slow and reverse rates of flow and that do not require assumptions of zero flow during the night are applicable to studies with roots. The heat ratio method and the constant power heat balance method fit these criteria, whereas the constant temperature heat balance, compensation heat pulse and thermal dissipation methods do not.

Capillary electrophoresis for the determination of major amino acids and sugars in foliage: application to the nitrogen nutrition of Sclerophyllous species

Amino acids and sugars are probably the most commonly measured solutes in plant fluids and tissue extracts. Chromatographic techniques used for the measurement of such solutes require complex derivatization procedures, analysis times are long and separate analyses are required for sugars and amino acids. Two methods were developed for the analysis of underivatized sugars and amino acids by capillary electrophoresis (CE). Separation of a range of sugars and amino acids was achieved in under 30 min, with good reproducibility and linearity. In general, there was close agreement between amino acid analyses by CE and HPLC with post-column derivatization. An alternative, more rapid method was optimized for the common neutral sugars. Separation of a mixture of fructose, glucose, sucrose, and fucose (internal standard) was achieved in less than 5 min. How the source of N applied (nitrate or ammonium) and its concentration (8.0 or 0.5 mM) affects the amino acid and sugar composition of leaves from Banksia grandis Willd. and Hakea prostrata R. Br. was investigated. The amino acid pool of Banksia and Hakea were dominated by seven amino acids (aspartic acid, glutamic acid, asparagine, glutamine, serine, proline, and arginine). Of these, asparagaine and glutamine dominated at low N-supply, whereas at high N-supply the concentration of arginine increased and dominated amino-N. Plants grown with nitrate had a greater concentration of proline relative to plants with ammonium. In Banksia the concentration of amides was greatest and arginine least with a nitrate N-source, whereas in Hakea amides were least and arginine greatest with nitrate N-source. The concentration of sugars was greater in Banksia than Hakea and in both species at greater N-supply.

Pre-penile arteries are dominant in the regulation of penile vascular resistance in the rat

The amount of blood flow into the penis that will produce an erection is dependent on the sum of inflow resistance from the feeder arteries, arterioles and the intra-penile vasculature. In the present study, our objective was to determine quantitatively the contribution to inflow resistance of these different components of the rat penile vasculature. Using methods developed previously, we determined the resistance properties of the isolated perfused whole penis in situ, both in an intact system and after serial transactions of the vessels. These cuts eliminated progressively larger distal segments of the vascular bed. Perfusion pressures were recorded at different flow rates (0.5-3 ml/min/kg body weight) under conditions of maximal dilatation and maximal vasoconstriction induced by methoxamine (MXA, 40 microg/ml). Regardless of the level of vascular tone, the pudendal artery contributes approximately 70% of the total resistance of the penile vasculature. In contrast, the vasculature within the penis (tip, shaft, crus) contributes only about one quarter of the resistance. Penile arterial inflow resistance properties both at maximal vasodilation and maximal alpha1-adrenergic constriction are dominated by the extra-penile vasculature in the rat. The implications of these findings are that alterations in the pudendal-artery (eg vasodilation, vasoconstriction, stenosis) would have primary control of arterial inflow and suggest an important role for pharmacological agents which can promote a more generalized vasodilation (eg phosphodiesterase inhibitors) in contrast to selective corpus cavernosal agents.

Triplet waves in a quantum spin liquid

We report a neutron scattering study of the spin- 1/2 alternating bond antiferromagnet Cu(NO3)(2);2.5D(2)O for 0.06<k(B)T/J1<1.5. For k(B)T/J1<<1 the excitation spectrum is dominated by a coherent singlet-triplet mode centered at J1 = 0.442(2) meV with sinusoidal dispersion and a bandwidth of J2 = 0.106(2) meV. A complete description of the zero temperature contribution to the scattering function from this mode is provided by the single mode approximation. At finite temperatures we observe exponentially activated band narrowing and damping. The relaxation rate is thermally activated and wave vector dependent with the periodicity of the reciprocal lattice.

Autonomic circulatory and cerebrocortical responses during increasing depth of propofol sedation/hypnosis in humans

PURPOSE

To describe the relative effects of graded central nervous system (CNS) depression, using increasing propofol infusion rates, on neurovegetative brainstem-mediated circulatory control mechanisms and higher cortical activity in healthy humans.

METHODS

Propofol was administered using an infusion scheme designed to achieve three target blood concentrations in ten healthy volunteers. Blood propofol concentrations and sedation scores were determined at baseline, during the three propofol infusion levels, and 30 min into the recovery period. Electroencephalographic (EEG) power was measured in three frequency bands to quantify cortical activity, and autonomic heart rate control was quantified using spontaneous baroreflex assessment and power spectral analysis of pulse interval.

RESULTS

Sedation scores closely paralleled propofol blood concentrations (0, 0.53 +/- 0.34, 1.24 +/- 0.21, 3.11 +/- 0.80, and 0.96 +/- 0.42 microg x mL(-1) at baseline, three infusion levels and recovery respectively), and all subjects were unconscious at the deepest level. Indices of autonomic heart rate control were decreased only at the deepest levels of CNS depression, while EEG effects were apparent at all propofol infusion rates. These EEG effects were frequency specific, with power in the beta band being affected at light levels of sedation, and alpha and delta power altered at deeper levels.

CONCLUSIONS

The results of this study support a relative preservation of neurovegetative circulatory control mechanisms during the early stages of CNS depression using gradually increasing rates of infusion of propofol. Indices of circulatory control did not reliably reflect depth of sedation.

Sudden and unexpected loading generates high forces on the lumbar spine

STUDY DESIGN

A cross-sectional study of spinal loading in healthy volunteers.

OBJECTIVES

To measure the bending and compressive forces acting on the lumbar spine, in a range of postures, when unknown loads are delivered unexpectedly to the hands.

SUMMARY OF BACKGROUND DATA

Epidemiologic studies suggest that sudden and unexpected loading events often lead to back injuries. Such incidents have been shown to increase back muscle activity, but their effects on the compressive force and bending moment acting on the spine have not been fully quantified. Furthermore, previous investigations have focused on the upright posture only.

METHODS

In this study, 12 volunteers each stood on a force plate while weights of 0, 2, 4, and 6 kg (for men, 40% less for women) were delivered into their hands in one of three ways: 1) by the volunteer holding an empty box with handles, into which an unknown weight was dropped; 2) by the same way as in 1, but with volunteer wearing a blindfold and earphones to eliminate sensory cues; or 3) by the volunteer sliding a box of unknown weight off a smooth table. Experiments were carried out with participants standing in upright, partially flexed, and moderately flexed postures. Spinal compression resulting from muscular activity was quantified using electromyographic signals recorded from the back and abdominal muscles. The axial inertial force acting up the long axis of the spine was calculated from the vertical ground reaction force. The bending moment acting on the osteoligamentous spine was quantified by comparing measurements of lumbar curvature with the bending stiffness properties of cadaveric lumbar spines.

RESULTS

The contribution from abdominal muscle contraction to overall spinal compression was small (average, 8%), as was the axial inertial force (average, 2.5%), and both were highest in the upright posture. Peak bending moments were higher in flexed postures, but did not increase much at the moment of load delivery in any posture. Peak spinal compressive forces were increased by 30% to 70% when loads were suddenly and unexpectedly dropped into the box, and by 20% to 30% when they were slid off the table, as compared with loads simply held statically in the same posture (P < 0.001). The removal of audiovisual cues had little effect.

CONCLUSIONS

Sudden and alarming events associated with manual handling cause a reflex overreaction of the back muscles, which substantially increases spine compressive loading. Manual handling regulations should aim to prevent such events and limit the weight of objects to be lifted.

Effects of an environmental anti-androgen on erectile function in an animal penile erection model

PURPOSE

Erectile function is testosterone dependent. For example, interference with either the levels or receptor binding of this steroid hormone may induce erectile dysfunction. Several environmental contaminants can interfere with the actions of endogenous hormones and have been termed 'endocrine disrupters.' p,p-DDE, a prominent and persistent metabolite of the insecticide DDT, has been shown to be an androgen receptor antagonist. The objective was to determine whether endocrine disrupters, as exemplified by p,p-DDE, are factors in the etiology of erectile dysfunction.

MATERIALS AND METHODS

Using the established rat model of apomorphine-induced (80 microg./kg, s.c.) erections we assessed the dose-response effects of p,p-DDE in comparison to the known androgen receptor antagonist flutamide in acute (0.5 to 12 hours) and short-term (up to 8 weeks) experiments in both intact (Study 1) and castrated (Study 2) rats. As a follow up (Study 3), castrated rats treated with p,p-DDE were given increasing doses of testosterone (0.48 to 2.4 mg./kg., i.p.), eight weeks after p,p-DDE administration, to assess reversibility of p,p-DDE effect.

RESULTS

A single dose of flutamide (50 mg./kg., i.p.) was found to significantly decrease apomorphine-induced erections to less than 50% over 12 hours following flutamide administration with recovery of erectile response within 48 hours. In comparison, a single dose of p,p-DDE (500 mg./kg., i.p.) decreased apomorphine-induced erections for at least two weeks (1.15+/-0.3 versus 2.5+/-1.1). Castration significantly decreased apomorphine-induced erections to approximately 0.5 erections/30 minutes. Flutamide (50 mg./kg.; i.p.) or p,p-DDE (50 mg./kg.; i.p.) did not further suppress the apomorphine erections in castrated rats. Testosterone supplementation (480 microg./kg; s.c.) in vehicle treated castrated rats recovered erectile response to pre-castrated levels, whereas p,p-DDE treated castrated rats required 4 times the dose of testosterone (2 mg./kg.; s.c.) given to vehicle treated rats to recover erections.

CONCLUSIONS

The endocrine disrupter p,p-DDE can markedly interfere with erectile function and demonstrates persistence after a single dose. This supports our novel concept that environmental hormones may cause erectile dysfunction.

The conditioned response erection (CRE)--a new approach to modelling erectile responses in the rat

Several animal models are currently used in erectile (dys)function research; these models fail to account for the conditions involving the more spontaneous erections in humans. Recently, we observed an increase in the number of 'spontaneously' occurring erections in rats with previous exposure to apomorphine (APO), a centrally acting drug that initiates penile erections and yawns. Based on this observation, we designed a series of experiments to characterize the development of enhanced, non-apomorphine-induced erections or 'spontaneous' erectile responses to vehicle administration in rats with previous exposure to APO. We further examined the effects of castration on these conditioned erections. Naive (ie never received APO) rats were administered vehicle (1 ml/kg saline) to determine the frequency of baseline erections and yawns. An alternating series of APO (80 microg/kg s.c.) and vehicle administrations were performed over several days and subsequent erectile and yawning responses were recorded. Following 3 sets of 3 APO administrations (with vehicle administered between sets), and the 3rd vehicle administration, these rats were then surgically castrated and allowed 30 days to recover. Following this, APO was administered 3 times to determine erectile and yawning responses post-castration, followed by vehicle administration to determine the effects of castration on conditioned APO responses. The major findings were: (1) that although naive rats had a basal spontaneous erectile response (0.75 +/- 0.88; 4 of 8 rats with at least one erection), repetitive administration (up to 22 treatments) of the central initiator apomorphine significantly increased the number of erections (1.8 +/- 0.7; 7 of 8 rats with at least one erection) and yawning (2.5 +/- 2.47) responses to vehicle administration; and (2) both spontaneous yawning and erectile responses were found to be androgen dependent since castration dramatically lowered the number of erections (0.13 +/- 0.35; 1 of 8 rats with at least one erection) and yawns (0). Therefore, this method of producing erections without a pharmacological manipulation provides an additional animal model which can be used in conjunction with the APO-induced erections in characterizing the physiology and pathophysiology of erectile function in conscious rats.

Effects of backward bending on lumbar intervertebral discs. Relevance to physical therapy treatments for low back pain

STUDY DESIGN

Mechanical testing of cadaveric motion segments.

OBJECTIVES

To test the hypothesis that backward bending of the lumbar spine can reduce compressive stresses within lumbar intervertebral discs.

SUMMARY OF BACKGROUND DATA

Lumbar extension affects the distribution of compressive stress inside normal cadaveric discs, but little is known about its effect on mechanically disrupted and degenerated discs.

METHODS

Nineteen lumbar motion segments (mean donor age, 48 years) were subjected to complex mechanical loading to simulate the following postures: moderate lumbar flexion, 2 degrees of extension, 4 degrees of extension, and the neutral position (no bending). The distribution of compressive stress within the disc matrix was measured in each posture by pulling a miniature pressure transducer along the midsagittal diameter of the disc. Stress profiles were repeated after a mechanical treatment that was intended to simulate severe disc degeneration in vivo.

RESULTS

The "degeneration" treatment reduced pressure in the nucleus pulposus and generated stress concentrations within the anulus, in a manner similar to that found in severely degenerated discs in vivo. When all discs were considered together, 2 degrees of extension increased the maximum compressive stress within the posterior anulus by an average of 16%, compared with the neutral posture. The size of localized stress peaks within the posterior anulus was increased by 43% (P = 0.02). In 4 degrees of extension, changes observed between 0 degree and 2 degrees were usually exaggerated. In contrast, moderate flexion tended to equalize the distribution of compressive stress. In 7 of the 19 discs, 2 degrees of lumbar extension decreased maximum compressive stress in the posterior anulus relative to the neutral posture by up to 40%. Linear regression showed that lumbar extension tended to reduce stresses in the posterior anulus in those discs that exhibited the lowest compressive stresses in the neutral posture (P = 0.003; R2 = 41%).

CONCLUSIONS

The posterior anulus can be stress shielded by the neural arch in extended postures, but the effect is variable. This may explain why extension exercises can relieve low back pain in some patients.

Irbesartan: review of pharmacology and comparative properties

The recently developed and marketed angiotensin II type 1 (AT1) receptor blockers (ARBs) have demonstrated efficacy equivalent to that of other leading classes of antihypertensive agents, with superior tolerability profiles. The specific targeting of the AT1 receptor afforded by these agents has demonstrated more complete blockade of the renin-angiotensin system than that offered by angiotensin-converting enzyme inhibitors. These data notwithstanding, differentiation within the class of ARBs has been limited. With the accumulation of additional data with ARBs, it has recently become possible to make within-class distinctions, based in large part on the individual pharmacological profiles of the ARBs. To this end, absorption, distribution, half-life, dose response and level of angiotensin II antagonism are of special note. When these properties are viewed as a group, the ARB irbesartan appears to offer advantages beyond those attained with other ARBs. Irbesartan is well absorbed, does not require biotransformation to an active metabolite to exert its antihypertensive activity, offers a large volume of distribution, has a half-life that is sufficient to allow once-daily dosing, is associated with a strong and consistent dose-response and has been demonstrated to provide a level of angiotensin II antagonism that is statistically superior to that offered by some other ARBs. These pharmacological differences may explain the clinical superiority of irbesartan compared with losartan, the first member of the ARB class. As even more data on the ARBs become available, the ability to determine the advantages of specific members of this class will be enhanced, distinctions that already have begun to come to light.

Personal risk factors for first-time low back pain

STUDY DESIGN

A prospective study of personal risk factors for first-time low back pain.

OBJECTIVES

To construct and validate a multivariate model to predict low back pain.

SUMMARY OF BACKGROUND DATA

Various physical and psychological factors have been reported to increase the risk of low back pain, but conflicting results may be attributable to inaccurate "clinical" measures and to poorly validated statistical models.

METHODS

A total of 403 health care workers aged 18-40 years volunteered for the study. None had any history of "serious" back pain requiring medical attention or time off work. The volunteers completed the following questionnaires: the modified somatic perception questionnaire, the Zung depression scale, and the Health Locus of Control. Anthropometric factors were quantified using standard techniques. The 3Space Isotrak device (Polhemus, VT) was used to measure lumbar curvature and hip and lumbar spine mobility. Leg and back strength and back muscle fatiguability were measured in functional postures. Postal follow-up questionnaires, sent after 6, 12, 18, 24, 30, and 36 months, inquired about back pain, and multivariate logistic regression was used to identify risk factors at each follow-up.

RESULTS

The response rate fell from 99% at 12 months to 90% at 36 months, at which time 90 volunteers reported "serious" back pain and 266 reported "any" back pain. The following were consistent predictors of serious back pain: reduced range of lumbar lateral bending, a long back, reduced lumbar lordosis, increased psychological distress, and previous nonserious low back pain. Only the latter three were consistent predictors of "any" back pain. Physical factors had the most influence in a sub-population of volunteers who were new to the job.

CONCLUSIONS

Personal risk factors explained up to 12% of first-time low back pain.

A rapid and simple method for processing wood to crude cellulose for analysis of stable carbon isotopes in tree rings

For analysis of carbon isotope discrimination in wood, cellulose or holocellulose is often preferred to whole tissue because of the variability in isotopic composition of different wood components and the relative immobility of cellulose. Most currently used methods for the preparation of wood components for stable isotope analysis (e.g., the Jayme-Wise method) produce a residue of holocellulose. The Jayme-Wise method was initially developed to extract holocellulose from small (~1 g) samples of wood, and, despite subsequent modifications, the method requires specialized glassware, considerable time and entails the risk of sample loss. For carbon isotope analysis, we adapted an acid-catalyzed solvolytic method for preparing crude cellulose by treating wood meal with acidified di-glycol methyl ether (diglyme). The one-step process requires no special glassware, is complete within 24 hours and enables over 100 samples to be processed in a day. This method gives similar delta(13)C values to the Jayme-Wise method for wood of Eucalyptus globulus Labill., Pinus radiata D. Don and Pinus pinaster Ait. The relationship between delta(13)C of wood and crude cellulose is as strong as that observed between wood and alpha-cellulose and stronger than that observed between wood and holocellulose in other species. These relationships suggest that variation in delta(13)C of wood may result from hemicellulose and that analysis of stable carbon isotopes in crude cellulose is preferable. If the consistent -0.3 bias in the value of delta(13)C of cellulose resulting from residual lignin is corrected for, then the relationship between delta(13)C of wood and crude cellulose may be used to predict delta(13)C of cellulose from a small sub-sample. The method is well suited to species with low concentrations of extractives, but further testing is needed to assess its general applicability.

Renal interstitial hydrostatic pressure and urinary sodium excretion in rats with angiotensin-converting enzyme inhibitor-induced papillary atrophy

The importance of angiotensin type-1 (AT1) receptor stimulation during renal development has recently been established in both pharmacological and knockout models. We have previously reported irreversible and progressive papillary atrophy and a reduced baseline renal interstitial hydrostatic pressure (RIHP) after neonatal angiotensin-converting enzyme (ACE) inhibition. The aim of the present study was to investigate the consequences of these abnormalities on urinary sodium excretion during acute extracellular sodium loading. Rats were treated neonatally with enalapril (10 mg kg-1 day-1) or saline control from days 3 to 23 after birth. Urinary sodium excretion was assessed in relation to mean arterial pressure (MAP) and RIHP responses in adult anaesthetised rats during moderate (1.5 and 3 % body weight) and severe (9 % body weight) saline-induced volume expansion. Control rats responded to the moderate volume expansion by increasing MAP by 16 +/- 6 % and RIHP by 40 +/- 23 %, respectively. In neonatally enalapril-treated rats, however, MAP and RIHP remained unchanged and were associated with a smaller increase in sodium excretion (44 +/- 11 % of the total amount infused versus 71 +/- 16 % for controls, P < 0.05). In contrast, severe volume expansion resulted in marked pressure rises in both the enalapril-treated group (36 +/- 12 and 112 +/- 48 % of baseline for MAP and RIHP, respectively) and the control group (34 +/- 21 and 130 +/- 34 % of baseline for MAP and RIHP, respectively). Moreover, the increases in MAP and RIHP were associated with complete excretion of the severe sodium challenge within 60 min in both treatment groups. We conclude that a RIHP response appears to be a prerequisite for adequate urinary sodium excretion in this model of papillary atrophy. Hence, an intact renal medulla is not mandatory in the renal handling of sodium during extracellular loading.

Prediction of maximal back muscle strength from indices of body mass and fat-free body mass

OBJECTIVES

The purpose of this study was to examine, in healthy volunteers, the relationship between back extensor muscle strength and body size.

METHODS

The maximal voluntary isometric back extensor strength of 456 volunteers, aged 18-42 yr and with no history of low back pain, was measured in a standing, slightly flexed forward posture. This was then correlated with two indices of body size: body mass and fat-free body mass.

RESULTS

Significant linear relationships were observed between back muscle strength and each of the two indices of body size. There was a gender difference in both the slope and the intercept of the regression equations describing the relationships. There was no independent influence of age within the range studied.

CONCLUSION

It was possible to establish predictive equations for back extensor strength based on body size which could be used to quantify strength 'deficits', for instance in patients with low back pain, and to prescribe submaximal target forces for use in endurance training and testing.

The penis is not protected--in hypertension there are vascular changes in the penis which are similar to those in other vascular beds

In hypertension, small arteries in a variety of vascular beds undergo structural changes that increase resistance. To assess whether there are differential structural changes in the penis that accompany hypertension, we began with determining structurally-based vascular resistance properties in penile and hindlimb vascular beds of adult spontaneously hypertensive rats (SHR) and Sprague-Dawley (SD) rats. In anesthetized SHR, the penile and hindlimb vasculature were isolated and perfused, maximum dilation was induced, and a flow-pressure assessment and alpha 1-adrenoceptor agonist concentration-response curves were generated. Both the baseline and maximum constrictor responses were similar in the two beds of each strain, and overall the maximum structurally-based vascular resistance in SHR was higher than in SD rats. Our data suggests that the penile vasculature is not protected from the structural changes that take place in the other vascular beds in hypertension. There does not appear to be an underlying functional control mechanism that protects the penile vasculature from structural changes that may have a negative impact on penile blood flow.

Differential regulation of IGF-I, its receptor and GH receptor mRNAs in the right ventricle and caval vein in volume-loaded genetically hypertensive and normotensive rats

It has been suggested, mainly by in vitro findings, that cardiovascular tissue in the spontaneously hypertensive rat (SHR) should be more prone to proliferate/hypertrophy than that of the Wistar-Kyoto rat (WKY). The present study tests the hypothesis that the tissue of the low-pressure compartment in SHR, being structurally similar to that of the WKY, shows an increased growth response due to activation of the GH-IGF-I system. An aortocaval fistula (ACF) was induced in 64 SHR and WKY male rats and 44 rats served as controls. They were all followed for 1, 2, 4 and 7 days after surgery. In separate groups of SHR (n=4) and WKY (n=3), central venous pressure was measured by telemetry recordings prior to opening of the fistula and for up to 16 h post-surgery. Systolic blood pressure was measured during the week post-surgery. The right ventricular (RV) and the caval vein IGF-I mRNA and RV IGF-I receptor and GH receptor mRNAs were quantitated by means of solution hybridisation assay. In rats with ACF the systolic blood pressure decreased, approximately 29% in SHR and 16% in WKY between 1 and 7 days post-surgery (P<0.05, n=5-6 in each group). SHR with ACF showed a transient elevation in central venous pressure vs WKY. Within the week following fistula induction both strains showed a similar, pronounced increase in RV hypertrophy. SHR with ACF showed a smaller, or even blunted, overall response with respect to activation of the GH-IGF-I system compared with WKY, the latter showing clear-cut elevation of gene expressions. Two days after shunt opening in SHR, RV and caval vein IGF-I mRNA increased by 57% and 108% (P<0.05 for both, n=5-6 in each group) respectively, and these expressions were then turned off, whereas RV GH receptor and IGF-I receptor mRNA expression remained unaffected compared with WKY rats. WKY rats showed on average a later and a greater response of GH-IGF-I system mRNA expression vs SHR. The present in vivo study suggests that the SHR requires less activation of the GH-IGF-I system for creating a given adaptive structural growth response.

Dynamic forces acting on the lumbar spine during manual handling. Can they be estimated using electromyographic techniques alone?

STUDY DESIGN

Compressive loading of the lumbar spine was analyzed using electromyographic, movement analysis, and force-plate techniques.

OBJECTIVES

To evaluate the inertial forces that cannot be detected by electromyographic techniques alone.

SUMMARY OF BACKGROUND DATA

Links between back pain and manual labor have stimulated attempts to measure spine compressive loading. However, direct measurements of intradiscal pressure are too invasive, and force plates too cumbersome for use in the workplace. Electromyographic techniques are noninvasive and portable, but ignore certain inertial forces.

METHODS

Eight men lifted boxes weighing 6.7 and 15.7 kg from the ground, while joint moments acting about L5-S1 were quantified 1) by using a linked-segment model to analyze data from Kistler force plates and a Vicon movement-analysis system, and 2) by measuring the electromyographic activity of the erector spinae muscles, correcting it for contraction speed and comparing it to moment generation during static contractions. The linked-segment model was used to calculate the "axial thrust," defined as the component of the L5-S1 reaction force that acts along the axis of the spine and that is unrelated to trunk muscle activity or static body weight.

RESULTS

Peak extensor moments predicted by the two techniques were similar and equivalent to spinal compressive forces of 2.9-4.8 kN. The axial thrust "hidden" from the electromyographic technique was negligible during slow lifts, and remained below 4% of peak spinal compression even during fast heavy lifts. Peak axial thrust was proportional to the peak vertical ground reaction (R2 = 0.74).

CONCLUSIONS

Electromyographic techniques can measure dynamic spinal loading, but additional force-plate data would improve accuracy slightly during lifts requiring a vigorous upward thrust from the legs.

Experimental determination of stress distributions in articular cartilage before and after sustained loading

OBJECTIVE

To test the hypotheses that stress concentrations exist within articular cartilage, and are intensified by sustained 'creep' loading.

DESIGN

Matched-pair comparison of stress distributions in cartilage, in vitro, before and after creep.

BACKGROUND

The ability of cartilage to equalize contact stresses between articulating surfaces may be compromised by undulations in the subchondral bone, and by variations in chemical composition. Furthermore, any stress concentrations within cartilage may be affected by creep loading, which-reduces its water content.

METHODS

Sixteen specimens of apparently normal cartilage-on-bone, 12 mm x 15 mm, were removed from the femoral condyles and tibial plateaux of patients undergoing total knee replacement. The cartilage was subjected to a nominal compressive stress of 2 MPa by means of a 10 mm-diameter flat impermeable indentor. During the 20 s loading period, a miniature pressure transducer, side-mounted in a 0.9 mm-diameter needle, was pulled through the cartilage in a direction parallel to the surface, while transducer output and position were sampled at 25 Hz. 'Stress profiles' were obtained with the transducer pointing in the 12 o'clock and 3 o'clock directions, and were repeated after creep loading at 1.6 MPa for 2 h.

RESULTS

Validation tests indicated that transducer output was proportional to the average compressive stress, but overestimated it by 9-15%. Stresses were greatest under the centre of the indentor, and showed local variations ('concentrations') which were increased in number and size after creep loading.

CONCLUSIONS

Measured values of compressive stress incorporate small systematic errors. Nevertheless, the results presented clearly support both hypotheses.

Short- and long-term enalapril affect renal medullary hemodynamics in the spontaneously hypertensive rat

Long-term angiotensin-converting enzyme (ACE) inhibition in the spontaneously hypertensive rat (SHR) resets pressure natriuresis and shifts the relationship between renal arterial pressure (RAP) and renal interstitial hydrostatic pressure (RIHP) to lower levels of arterial pressure. These effects persist after withdrawal of treatment. The purpose of this study was to determine the effect of short- and long-term ACE inhibition on medullary blood flow (MBF). Enalapril (25 mg. kg-1. day-1 in drinking water) was given to male SHR from 4 to 14 wk of age. Four weeks after stopping treatment, we measured MBF over a wide range of RAP using laser-Doppler flowmetry in anesthetized rats. Additional rats, either untreated or previously treated for 10 wk, received 3-day enalapril treatment just before the experiment. MAP (mmHg +/- SE) was 178 +/- 6 (n = 8), 134 +/- 6 (n = 8), 138 +/- 5 (n = 9), and 111 +/- 6 mmHg (n = 9) for the untreated, 3 day, 10 wk, and 10 wk + 3 day groups, respectively. Total renal blood flow for the groups receiving 3-day treatment was significantly higher when compared with that in rats with an intact renin-angiotensin system. Three-day treatment had no effect on the relationship between RAP and RIHP, whereas that in rats receiving 10-wk treatment was shifted to lower levels of RAP by approximately 30 mmHg. Both 10-wk and 3-day treatment independently increased the slope of the RAP versus MBF relationship at values of RAP > 100 mmHg. The slopes in perfusion units/mmHg were 0.12 +/- 0.01 (n = 8), 0.26 +/- 0.01 (n = 8), 0.27 +/- 0.01 (n = 9), and 0.30 +/- 0.02 (n = 9) for the untreated, 3 day, 10 wk, and 10 wk + 3 day groups, respectively. These results indicate that the effect of short-term and the persistent effect of long-term enalapril alter renal medullary hemodynamics in a way that may contribute to the resetting of the pressure-natriuresis relationship in treated rats.

Simultaneous determination by capillary gas chromatography of organic acids, sugars, and sugar alcohols in plant tissue extracts as their trimethylsilyl derivatives

A capillary gas chromatographic (GC) method for the simultaneous determination of organic acids, sugars, and sugar alcohols extracted from plant tissues is described. Plant leaves were extracted in 5% (w/v) perchloric acid and neutralized extracts were purified using C18 cartridges. Organic acids, sugars, and sugar alcohols in purified extracts were converted to their trimethylsilyl (TMS)/TMS-oxime derivatives prior to separation and detection by capillary GC with flame ionization detection (FID). Derivatization procedures were investigated in detail and the compounds of interest were readily converted to their TMS/TMS-oxime derivatives using hexamethyldisiazane reagent in acetonitrile solvent (1:6 v/v) at 100 degreesC for 60 min. The derivatives were sufficiently volatile and stable. The FID response to derivatized compounds was generally linear in the concentration range 30-300 microg ml-1, with detection limits in the order of 3-76 ng. The proposed method was demonstrated for the determination of organic acids, sugars, and sugar alcohols in leaf extracts of two native Australian plants.

Long-term reduction of renal interstitial hydrostatic pressure after neonatal renin-angiotensin system inhibition in the rat

BACKGROUND

Neonatal inhibition of the renin angiotensin system (RAS) causes a decreased urinary concentrating ability, papillary atrophy, and tubulointerstitial inflammation long term. As a consequence of these morphological changes, we surmised that renal blood flow and renal interstitial hydrostatic pressure (RIHP) may be altered during and shortly after cessation of neonatal angiotensin-converting enzyme (ACE) inhibition, and that tentative changes of these variables would persist long after treatment withdrawal.

METHODS

Rats were given daily intraperitoneal injections of the ACE inhibitor, enalapril (10 mg/kg) or saline from days 3 to 23 postpartum, and the relationship between renal perfusion pressure (PP) and RIHP was investigated in 6- and 13-week-old anaesthetized rats.

RESULTS

Neonatal ACE inhibition did not affect baseline RIHP short term, whereas RIHP was reduced at 13 weeks of age versus controls (11.6+/-1.6 vs 18.5+/-1.0 mmHg, P<0.05). Changes in RIHP correlated positively to changes in renal PP, independent of treatment and age (slope averaged 0.11+/-0.03). Ongoing ACE inhibition until 6 weeks of age neither affected baseline RIHP nor altered the reactivity to changes in perfusion pressure. Mild renal histopathological abnormalities were present already 3 weeks after cessation of treatment and were aggravated significantly in the 13-week-old rats, showing a complete loss of the papillary parenchyma.

CONCLUSION

The reduced baseline RIHP in adult rats seemed to constitute a functional correlate to the major papillary atrophy. However, RIHP responses to changes in renal perfusion pressure was maintained, possibly indicating a compensatory effect of the remaining vasa recta and/or peritubular capillary network. Taken together, lack of neonatal angiotensin II type-1 (AT1) receptor stimulation induces not only irreversible abnormalities of the renal architecture, but causes alteration of intrarenal haemodynamics, such as a reduced RIHP, which may have implications for the regulation of pressure-natriuresis.

The compressive strength of articular cartilage

Articular cartilage provides the smooth bearing surfaces in freely moving (synovial) joints. Its mechanical properties are important because structural failure of cartilage is closely associated with joint disorders, including osteoarthritis. Some mechanical properties of cartilage are well characterized, but little is known about its compressive strength. A technique for measuring cartilage compressive strength is evaluated, and an overview of experiments which relate strength to stiffness and tissue hydration is given. Specimens of bovine articular cartilage-on-bone, approximately 15 mm square, were loaded on a hydraulic materials testing machine using flat impermeable indentors. Linear-ramp loading/unloading cycles of 1 s duration, and of increasing severity, were applied until failure was evident on force-displacement graphs. Some specimens were tested following a 30 min period of creep loading. Inkstaining and histology were used to locate the site of initial damage to each specimen. Specimen failure occurred first in the cartilage surface layer at a nominal applied stress of 14-59 MPa (mean 35.7 MPa). Mechanical properties were little affected by specimen or indentor size, provided both remained within defined limits, and compressive strength could be measured to an accuracy of approximately +/- 5 per cent. Compressive stiffness was a significant predictor of strength, but only if it was measured at high levels of stress. Strength increased following creep-induced water loss, and initial mechanical damage could propagate under moderate cyclic loading. This technique for measuring cartilage compressive strength has potential for investigating the causes of cartilage failure in vivo.

When is a lifting movement too asymmetric to identify low-back loading by 2-D analysis?

In ergonomics research, two-dimensional (2-D) biomechanical models are often used to study the mechanical loading of the low back in lifting movements. When lifting movements are asymmetric, errors of unknown size may be introduced in a 2-D analysis. In the current study, an estimation of these errors was made by comparing the outcome of a 2-D analysis to the results of a recently developed and validated 3-D model. Four subjects made two repetitions of five lifting movements, differing in the amount of asymmetry. The results showed a significant underestimation of the peak torque by 20, 36 and 61% when the initial position of a box was rotated 30, 60 and 90 degrees with respect to the sagittal plane of the subject. The main cause of this underestimation was a pelvic twist, resulting in an erroneous projection of a pelvic marker on to the sagittal plane due to pelvic twist. It is suggested that from 30 degrees box rotation a 2-D analysis may easily lead to wrong conclusions when it is used to study asymmetric lifting.

Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine

During manual handling, the back muscles protect the spine from excessive flexion, but in doing so impose a high compressive force on it. Epidemiological links between back pain and repetitive lifting suggest that fatigued muscles may adversely affect the balance between bending and compression. Fifteen volunteers lifted and lowered a 10 kg weight from floor to waist height 100 times. Throughout this task, the bending moment acting on the osteoligamentous lumbar spine was estimated from continuous measurements of lumbar flexion, obtained using the 3-Space Isotrak. Spinal compression was estimated from the electromyographic (EMG) activity of the erector spinae muscles, recorded from skin-surface electrodes at the levels of T10 and L3. EMG signals were calibrated against force when subjects pulled up on a load cell, and correction factors were applied to account for changes in muscle length and contraction velocity. Fatigue in the erector spinae muscles was quantified by comparing the frequency content of their EMG signal during static contractions performed before, and immediately after, the 100 lifts. Results showed that peak lumbar flexion increased during the 100 lifts from 83.3 +/- 14.8% to 90.4 +/- 14.3%, resulting in a 36% increase in estimated peak bending moment acting on the lumbar spine (P = 0.008). Peak spinal compression fell by 11% (p = 0.007). The median frequency of the EMG signal at L3 decreased by 5.5% following the 100 lifts (p = 0.042) confirming that the erector spinae were fatigued, but measures of fatigue showed no significant correlation with increased bending. We conclude that repetitive lifting induces measurable fatigue in the erector spinae muscles, and substantially increases the bending moment acting on the lumbar spine.

Simultaneous analysis of amino and organic acids in extracts of plant leaves as tert-butyldimethylsilyl derivatives by capillary gas chromatography

The simultaneous determination of amino and organic acids in plant tissue extracts using capillary gas chromatography is described. Plant leaves were extracted in 5% (w/v) perchloric acid and neutralized extracts were purified using C18 cartridges. The amino and organic acids in purified extracts were then converted to tert-butyldimethylsilyl (TBDMS) derivatives prior to separation and detection by capillary gas chromatography (GC) with flame ionization detection. Conditions required for optimal derivatization were investigated. Amino and organic acids were readily converted to their TBDMS derivatives using N-methyl-N-tert-butyldimethylsilyltrifluoroacetamide in dimethylformamide solvent 1:6 (v/v) with an average recovery of 90% and a reproducibility of about 5%. The characteristic [M-57] and [M-159] fragment ion of the TBDMS derivatives was confirmed using GC-MS. The proposed method was demonstrated by the determination of amino and organic acids in extracts of Acacia and Eucalyptus leaves, where detection limits were 1-20 ng.

Inhibited expression of insulin-like growth factor I mRNA and attenuated cardiac hypertrophy in volume overloaded hearts treated with difluoromethylornithine

The present study examined whether the previously reported hypertrophy and increased expression of insulin-like growth factor I (IGF-I) mRNA in the volume-overloaded right ventricle was dependent on an intact production of polyamines. Volume overload was created in normotensive Wistar rats by means of an aorto-caval fistula. Difluoromethylornithine (DFMO) 2%, which is a specific, irreversible blocker of ornithine decarboxylase, was administered in the drinking water to intervention groups and one sham group, respectively, 24 h prior to surgery and for up to 26 days. DFMO blocked transiently the early over-expression of right ventricular IGF-I mRNA and attenuated the rapid development of both right and left ventricular hypertrophy during volume overload. Expression of IGF-I mRNA in the right ventricle in the early phase of volume overload appears to be dependent on activation of ornithine decarboxylase, whereas other pathways are involved in the later phase of cardiac structural adaptation. Thus, these findings link together early and late growth responses potentially important for compensatory cardiac hypertrophy.

Acquired immunodeficiency syndrome dementia complex

Acquired immunodeficiency syndrome (AIDS) has become an epidemic in the United States. AIDS dementia complex (ADC) is a neurological dysfunction which has been indicated in 25-90% of AIDS patients, 30-40% of HIV-infected patients, and may be the only presenting manifestation of AIDS. Researchers have investigated many aspects of ADC including clinical features, etiology, epidemiology and prevalence, diagnosis (psychological parameters and laboratory investigations such as CSF, EEG, CT, MRI, PET, and ERP), assessment, neurological features (including neuropsychiatric and neuropsychological measures, and neuropathology), prognosis, and treatment. The research is controversial, complex, and contradictory. A discussion of the many areas of ADC and many hypotheses will be included.

Could sudden increases in physical activity cause degeneration of intervertebral discs?

Epidemiological studies link high repetitive loading of the lower back with degeneration of intervertebral discs, and experiments on cadaver spines confirm that repetitive mechanical loading can disrupt the lumbar discs in a manner characteristic of "degeneration". But why do living discs not just strengthen in response to this stimulus, as other musculo-skeletal tissues do? Our hypothesis proposes that the low metabolic rate of lumbar discs (the largest avascular structures in the body) prevents them from keeping pace with adaptive remodelling changes in adjacent tissues, so that large and abrupt increases in a person's level of physical activity may leave the lumbar discs the weak link in a strengthening and heavily loaded spine. Recent laboratory investigations support the hypothesis, but clinical evidence is required to relate recent disc degeneration with recent increases in physical activity, and so test the hypothesis.

A therapeutic taxonomy of treatments for erectile dysfunction: an evolutionary imperative

AIM OF THE STUDY

A functional classification of treatments for erectile dysfunction is important but none exists at present. Advances in the understanding of the mechanisms of drug action and of the mechanisms of penile erection suggest that there is now a rational basis for a therapeutic classification, with the expectation that a logical diagnostic classification will follow.

METHODS

The currently available treatments for erectile function and the known relevant basic science were reviewed and assessed. From this, and analysis of classification systems in other fields, a classification was proposed and evaluated with respect to existing treatments.

RESULTS

The treatments for erectile dysfunction were classified into five major classes by their mode of action: (I) Central Initiators, (II) Peripheral Initiators, (III) Central Conditioners, (IV) Peripheral Conditioners and (V) Other. Drugs in these classes are further subdivided by the routes of administration and the mechanisms of specificity.

CONCLUSIONS

It is possible to analyze all known treatments using this classification. The principles of this scheme should be sufficiently clear as to enable knowledgeable specialists to arrive at similar conclusions about a drug. The classification proposed is general enough such that most new drugs should fall within a class. However, it should be modified if necessary, if new therapeutic agents can not be appropriately classified. It is our conclusion that with such endeavours the specialty itself and national regulatory bodies will find it easier to define and control how to apply new drugs, how to evaluate new drugs, and how to establish reasonable equivalences among agents and in whom these drugs and devices should be used.

Blunted cardiovascular growth induction during prolonged nitric oxide synthase blockade

The goal of the present study was to characterize the activation profile of the growth-related enzyme ornithine decarboxylase (ODC) in cardiovascular tissue during hypertension induced by chronic NO synthase blockade in relation to the development of structurally based changes in the heart and blood vessels. In previously instrumented conscious rats, mean arterial pressure and ODC activation were measured in cardiovascular tissue of rats treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg per day P.O.) for 4 hours and 1, 6, and 12 days. After 12 days of L-NAME treatment alone or in combination with 3% L-ornithine, structurally based hindlimb resistance properties were assessed. A marginal activation of ODC in the left ventricle and aorta was seen at 4 hours but returned to control levels at 1, 6, and 12 days of L-NAME treatment. A slightly prolonged yet transient activation of ODC occurred in the mesenteric vascular bed. Structurally based hindlimb vascular resistance was enhanced by 15% at maximum vasoconstrictor tone, and no change in cardiac mass occurred with L-NAME treatment. L-NAME+3% L-ornithine treatment resulted in a similar level of structural upregulation compared with L-NAME treatment alone. In summary, 12 days of L-NAME treatment resulted in only a modest change in vascular resistance, and only at maximum constriction, and no cardiac hypertrophy despite the presence of marked hypertension. The results of the present study indicate that either (1) pressure alone is not a sufficient stimulus to induce cardiovascular growth processes or (2) L-NAME may be "nonspecifically" inhibiting cardiovascular growth processes.

Preliminary assessment of potential health hazards associated with barium leached from glazed ceramicware

Ceramic glazes contain several elements which have the potential to leach into food or beverages that are held or stored in ceramicware. Recently, barium salts have been investigated as one of the alternatives to lead in frit formulations for glazes. This preliminary evaluation addresses the potential health hazards associated with barium at levels that might leach from glazed ceramicware. A set of specialty ceramicware, consisting of five teacups and a pitcher, was examined for extractable barium. Exposure to barium that adults (18-44 years) might encounter using the vessels for coffee, tea, or orange juice was estimated. The exposure estimate was derived from values for intakes of the beverages and for the barium migration from glazed ceramicware test samples. An established reference dose (RfD) for barium exposure for the critical effect of hypertension was identified. The potential hazard associated with the leaching of barium from glazed ceramicware varied with the level of use. Consuming beverages in amounts up to the 95th percentile would not result in total barium intake in amounts that exceed the RfD; consuming large quantities (> 95th percentile) of beverages such as tea or coffee from glazed vessels might. This suggests that for a small portion of the population of users, intake of barium may be in quantities that warrant further consideration as a potential health hazard. Analyses of a broad sample of ceramicware and study of barium leaching behaviour under actual use conditions are needed to assess further the significance of these findings.