The Athlete's Heart-Challenges and Controversies: JACC Focus Seminar 4/4

Regular exercise promotes structural, functional, and electrical remodeling of the heart, often referred to as the "athlete's heart," with intense endurance sports being associated with the greatest degree of cardiac remodeling. However, the extremes of exercise-induced cardiac remodeling are potentially associated with uncommon side effects. Atrial fibrillation is more common among endurance athletes and there is speculation that other arrhythmias may also be more prevalent. It is yet to be determined whether this arrhythmic susceptibility is a result of extreme exercise remodeling, genetic predisposition, or other factors. Gender may have the greatest influence on the cardiac response to exercise, but there has been far too little research directed at understanding differences in the sportsman's vs sportswoman's heart. Here in part 4 of a 4-part seminar series, the controversies and ambiguities regarding the athlete's heart, and in particular, its arrhythmic predisposition, genetic, and gender influences are reviewed in depth.

Self-reported motivations for engaging or declining to engage in cyber-dependent offending and the role of autistic traits

Cyber-dependent offending, i.e. criminal behaviour reliant on computing and the online domain, has been reportedly associated with particular characteristics and motivations such as being young, male, autistic and motivated by challenge. These associations are anecdotal however and empirical evidence is limited. The present study investigated reasons for engaging or declining to commit cyber-dependent offending in cyber-skilled non-offenders (n = 175) and offenders (n = 7) via an online survey measuring cyber-dependent criminality. The potential role of autism and autistic traits was also considered. Qualitative interviews about motivations for offending were carried out with the offenders. The cyber-dependent offenders reported seven main reasons for engaging in cyber-dependent offending: (1) lack of understanding; (2) entertainment; (3) peer influence; (4) experience and career; (5) anonymity and risk perception; (6) life events; and (7) morals. Twenty-nine (approximately 17 %) of the non-offenders had been asked to engage in cyber-dependent offending but had declined. Their reasons and motivations for declining to commit cyber-dependent offences were compared with the cyber-dependent offenders reasons and motivations for engaging in cybercrime. Seven main reasons for declining to offend were identified: (1) moral principles; (2) perception of risk; (3) fear of consequences; (4) not wanting to; (5) wanting to adhere to the law; (6) behaviour being too complicated; and (7) price being too low. Implications for practise are discussed.

Differentiating Athlete's Heart From Cardiomyopathies - The Left Side

In athletes who undertake a high volume of high intensity exercise, the resultant changes in cardiac structure and function which develop as a result of physiological adaptation to exercise (so called "Athlete's Heart") may overlap with some features of pathological conditions. This chapter will focus on the left side of the heart, where left ventricular cavity enlargement, increase in left ventricular wall thickness and increased left ventricular trabeculation associated with athletic remodelling may sometimes be difficult to differentiate from conditions such as dilated cardiomyopathy, hypertrophic cardiomyopathy or isolated left ventricular non-compaction. The distinction between physiological versus pathological changes in athletes is imperative as an incorrect diagnosis can have important consequences, such as exclusion from competitive sport, or false reassurance and missed opportunity for effective therapeutic intervention.

Relationship between Inflammatory Cytokines and Indices of Cardiac Dysfunction following Intense Endurance Exercise

Objectives

Pro-inflammatory cytokines have been noted to increase following exercise but their relationship to exercise-induced cardiac dysfunction has not previously been investigated. We sought to evaluate whether exercise-induced cardiac dysfunction was associated with increases in cytokines, particularly the pro-inflammatory cytokines IL-1β, IL-12p70 and TNFα, which have been most implicated in cardiac pathology.

Methods

40 well-trained endurance athletes underwent evaluation prior to and immediately following one of four endurance sporting events ranging from 3 to 11 hours duration. Cytokines (IL-1β, IL-6, IL-8, IL-10, IL-12p70 and TNFα) were analyzed by flow cytometry from serum samples collected within 50 minutes of race completion. Cardiac troponin (cTnI) and B-type natriuretic peptide were combined with an echocardiographic assessment of cardiac function, and a composite of cTnI > 0.04 μg/L, BNP increase > 10 ng/L and a decrease in right ventricular ejection (RVEF) > 10% were prospectively defined as evidence of myocardial dysfunction.

Results

Relative to baseline, IL-6 IL-8 and IL-10 increased 8.5-, 2.9-, and 7.1-fold, respectively, P<0.0001. Thirty-one (78%), 19 (48%) and 18 (45%) of the athletes met the pre-specified criteria for significant cTnI, BNP and RVEF changes, respectively. TNFα, IL-12p70 were univariate predictors of ΔRVEF and ΔBNP whilst none of the anti-inflammatory cytokines were significantly associated with these measures. Ten athletes (25%, all athletes competing in the endurance event of longest duration) met criteria for exercise-induced myocardial dysfunction. In these 10 athletes with myocardial dysfunction, as compared to those without, there was significantly greater post-race expression of the pro-inflammatory cytokines IL-12p70 (8.1±3.8pg/ml vs. 2.5±2.6pg/ml, P<0.0001) and TNFα (6.5±3.1pg/ml vs. 2.0±2.5pg/ml, P<0.0001).

Conclusion

Cardiac dysfunction following intense endurance exercise was associated with increased expression of pro-inflammatory cytokines. This does not prove a causal relationship but provides rationale for further investigations into whether inflammation mediates exercise-induced myocardial dysfunction.

Early repolarization patterns associated with increased arrhythmic risk are common in young non-Caucasian Australian males and not influenced by athletic status

BACKGROUND

Early repolarization (ER) with a horizontal ST segment (ST-h) and high-amplitude J waves in the inferior leads is associated with an increased risk of cardiac arrhythmic death. The effect of ethnicity and athletic status on this increased-risk ER pattern has not been established. Aboriginal Australian/Torres Strait Islander and Pacific Islander/Maori (non-Caucasian [non-C]) subjects are well represented in Australian sport; however, the patterns and prevalence of ER in these populations are unknown.

OBJECTIVE

The purpose of this study was to assess the prevalence and effect of athletic activity on ER patterns in young non-C and Caucasian (C) subjects.

METHODS

Twelve-lead ECGs of 726 male athletes (23.8% non-C) and 170 male controls (45.9% non-C) aged 16-40 years were analyzed for the presence of ER, defined as J-point elevation (J wave, QRS slur, or discrete ST elevation) ≥0.1 mV in ≥2 inferior (II, III, aVF) or lateral (I, aVL,V4-V6) leads. ST morphology was coded as horizontal (ST-h) or ascending (ST-a). "Increased-risk ER" was defined as inferior ER with ST-h and J waves >2 mV.

RESULTS

Regardless of athletic status, ER and increased-risk ER were more prevalent in non-C than in C subjects (53.8% vs 32% and 7.6% vs 1.2%, respectively, P <.0001). Whereas lower heart rate, larger QRS voltage, and shorter QRS duration were predictors of ER, non-C ethnicity was the only independent predictor of increased-risk ER (odds ratio 17.621, 95% confidence interval 4.98-62.346, P < .0001).

CONCLUSION

ER patterns associated with increased arrhythmic risk are more common in young non-C than C subjects and were not influenced by athletic status. The long-term clinical significance of ER in these populations is yet to be determined.

Effect of perceiving computing to be an acquirable skill upon a computer-mediated serial recall task

Serial recall tasks assess the capacity of verbal short-term memory. The perception of computing as an acquirable skill rather than a fixed ability affected performance upon computer-based serial recall tasks but did not affect performance on comparable pencil-and-paper tasks. Computerized versions of traditional assessments should control for this.

Is estradiol cardioprotection a nitric oxide-mediated effect?

BACKGROUND

Estradiol exerts a number of biological effects that support extensive observational data suggesting a protective role for estrogen in cardiovascular disease prevention. These include effects on lipid and carbohydrate metabolism, coagulation/fibrinolysis as well as a possible effect on vascular reactivity. It has been proposed that this might be mediated by vascular endothelial nitric oxide (NO) production. Accordingly, we designed complementary in-vivo and in-vitro studies to investigate this hypothesis further.

METHODS

Firstly, in a group of 10 healthy post-menopausal women, bilateral venous occlusion plethysmography was used to examine forearm vasoconstrictor responses to intrabrachial N(G)-monomethyl-l-arginine (l-NMMA; a substrate inhibitor of nitric oxide synthase) both before and after 4 weeks of treatment with transdermal 17beta-estradiol (E(2)) (80 microg/day). Secondly, we examined the direct effects of acute (24 h) and chronic (7 days) treatment with E(2) (10 pmol/l and 10 nmol/l) on endothelial nitric oxide synthase (eNOS) gene expression in cultured human aortic endothelial cells.

RESULTS

No significant differences were observed between the vasoconstrictor responses to l-NMMA (2, 4, 8 micromol/min) before and after E(2) treatment. Comparison of E(2)-treated endothelial cells with control cells showed no significant increase in eNOS mRNA expression following either acute or chronic estradiol treatment.

CONCLUSIONS

The present studies do not provide evidence for an eNOS-mediated cardioprotective response to estrogen and therefore suggest that additional mechanisms other than the endothelial NO system may have an important role in the cardiovascular effects of estrogen.

Adenovirus-mediated overexpression of extracellular superoxide dismutase improves endothelial dysfunction in a rat model of hypertension

Gene transfer may be appropriate for therapeutic protocols targeted at the vascular endothelium. Endothelial dysfunction is the principal phenotype associated with atherosclerosis and hypertension. Oxidative stress has been implicated in the development of endothelial dysfunction. We have explored the ability of overexpressing anti-oxidant genes (superoxide dismutases; SODs) in vitro and in vivo to assess their potential for reversing endothelial dysfunction in a rat model, the stroke-prone spontaneously hypertensive rat (SHRSP). Western blotting and immunofluorescence assays in vitro showed efficient overexpression of MnSOD and ECSOD with respect to localisation to the mitochondria and extracellular surface, respectively. Transgene functional activity was quantified with SOD activity assays. MnSOD and ECSOD overexpression in intact SHRSP vessels in vivo led to endothelial and adventitial overexpression. Pharmacological assessment of transduced vessels following in vivo delivery by basal NO availability quantification demonstrated that the "null" adenovirus and MnSOD adenovirus did not significantly increase NO availability. However, AdECSOD-treated carotid arteries showed a significant increase in NO availability (1.91 +/- 0.04 versus 0.75 +/- 0.08 g/g, n = 6, P = 0.029). In summary, efficient overexpression of ECSOD, but not MnSOD in vivo, results in improved endothelial function in a rat model of hypertension and has important implications for the development of endothelial-based vascular gene therapy.

Mapping and sequencing rat dishevelled-1: a candidate gene for cerebral ischaemic insult in a rat model of stroke

A quantitative trait locus on chromosome 5 in the rat is linked to sensitivity to brain ischemia in the stroke-prone spontaneously hypertensive rat (SHRSP). The genes encoding atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) that map to this location have been excluded as candidate genes. We examined dishevelled-1 (DVL-1) as a further candidate gene. DVL-1 had not yet been identified in the rat, but Anp, Bnp, and DVL-1 map to the homologous regions of the rat chromosome 5 quantitative trait locus in both mice and man. Furthermore, DVL-1 is involved in the Notch signalling system, which plays a role in the disorder cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, the symptoms of, which include ischaemic stroke. We show with radiation hybrid mapping that rat DVL-1 indeed maps to chromosome 5, where it is positioned immediately next to microsatellite marker D5Rat49. We sequenced the complete coding sequence and a large part of the intronic genomic sequence for the SHRSP strain and its reference Wistar-Kyoto strain. The DVL-1 sequence in the two strains was identical. Our results essentially exclude the DVL-1 gene as the cause for sensitivity to cerebral ischaemic insult in this rat model of stroke.

Analysis of cell-specific promoters for viral gene therapy targeted at the vascular endothelium

The use of viral vectors for vascular gene therapy targeted at the endothelium is limited by the promiscuous tropism of vectors and nonspecificity of viral promoters, resulting in high-level transgene expression in multiple tissues. To evaluate suitable endothelial cell (EC)-specific promoters for vascular gene therapy, we directly compared the ability of the fms-like tyrosine kinase-1 (FLT-1), intercellular adhesion molecule-2 (ICAM-2), and von Willebrand factor (vWF) promoters to drive EC-restricted transcription after cloning into adenoviral vectors upstream of lacZ. Vastly different expression profiles were observed. Whereas both FLT-1 and ICAM-2 promoters generated transgene expression levels similar to cytomegalovirus in ECs in vitro, vWF expression levels were extremely low. Analysis of non-EC types revealed that ICAM-2 but not FLT-1 evoked leaky transgene expression, thus identifying FLT-1 as the most selective promoter. With an ex vivo human gene therapy model, the FLT-1 promoter demonstrated EC-specific transgene expression in intact human vein but no detectable expression from infected exposed smooth muscle cells in EC-denuded vein. Furthermore, when adenoviruses were systemically administered to mice, the FLT-1 promoter demonstrated extremely low-level gene expression in the liver, the major target organ for adenoviral transduction in vivo. This study highlights the potential of using the FLT-1 promoter for local and systemic human gene therapy in hypertension and its complications.

Oxidative stress and vascular damage in hypertension

Oxidative stress, a state of excessive reactive oxidative species activity, is associated with vascular disease states such as hypertension. In this review, we discuss the recent advances in the field of reactive oxidative species-mediated vascular damage in hypertension. These include the identification of redox-sensitive tyrosine kinases, the characterization of enzymatic sources of superoxide production in human blood vessels, and their relationship with vascular damage in atherosclerosis and hypertension. Finally, recent developments in the search for strategies to attenuate vascular oxidative stress are reviewed.

Superoxide excess in hypertension and aging: a common cause of endothelial dysfunction

There is evidence in humans that hypertension and aging similarly impair endothelial function, although the mechanism remains unclear. Superoxide anion (O(2)(-)) is a major determinant of nitric oxide (NO) bioavailability and thus endothelial function. We sought to determine the relationship between endothelial function, O(2)(-), and age in normotensive Wistar-Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Aortic rings were removed from female WKY and SHRSP at 3 to 4 months (young) and 9 to 12 months (old). O(2)(-) generation by aortic rings was measured before and after removal of the endothelium or incubation with N(G) nitro-L-arginine methyl ester, diphenyleneiodonium, or apocynin. Levels of p22phox were studied with immunohistochemistry and used as a marker of NAD(P)H oxidase expression. NO bioavailability was significantly lower in old WKY compared with young WKY (P=0.0009) and in old SHRSP compared with young SHRSP (P=0.005). O(2)(-) generation was significantly greater in old WKY compared with young WKY (P=0.0001). Removal of the endothelium and N(G) nitro-L-arginine methyl ester treatment resulted in a significant reduction in O(2)(-) generation in old SHRSP (P=0.009 and 0.001, respectively). Diphenyleneiodonium significantly reduced O(2)(-) generation in 12-month WKY (P=0.008) and 12-month SHRSP (P=0.009). Apocynin attenuated O(2)(-) generation by older WKY (P=0.038) and SHRSP (P=0.028). p22phox was increased in older animals compared with young. We conclude that NO bioavailability decreases with age in female WKY and SHRSP. O(2)(-) generation increases with age in WKY and is higher in SHRSP and may contribute to the reduced NO by scavenging. NAD(P)H oxidase may contribute to the age-related increase in O(2)(-).

Impaired interval exercise responses in elite female cyclists at moderate simulated altitude

The effect of hypoxia on the response to interval exercise was determined in eight elite female cyclists during two interval sessions: a sustained 3 x 10-min endurance set (5-min recovery) and a repeat sprint session comprising three sets of 6 x 15-s sprints (work-to-relief ratios were 1:3, 1:2, and 1:1 for the 1st, 2nd, and 3rd sets, respectively, with 3 min between each set). During exercise, cyclists selected their maximum power output and breathed either atmospheric air (normoxia, 20.93% O(2)) or a hypoxic gas mix (hypoxia, 17.42% O(2)). Power output was lower in hypoxia vs. normoxia throughout the endurance set (244+/-18 vs. 226+/-17, 234+/-18 vs. 221+/-25, and 235+/-18 vs. 221+/-25 W for 1st, 2nd, and 3rd sets, respectively; P< 0.05) but was lower only in the latter stages of the second and third sets of the sprints (452+/-56 vs. 429+/-49 and 403+/-54 vs. 373+/- 43 W, respectively; P<0.05). Hypoxia lowered blood O(2) saturation during the endurance set (92.9+/-2.9 vs. 95.4+/-1.5%; P<0.05) but not during repeat sprints. We conclude that, when elite cyclists select their maximum exercise intensity, both sustained (10 min) and short-term (15 s) power are impaired during hypoxia, which simulated moderate ( approximately 2,100 m) altitude.

Gene transfer of endothelial nitric oxide synthase but not Cu/Zn superoxide dismutase restores nitric oxide availability in the SHRSP

OBJECTIVE

Previous studies from our group have shown a deficit in nitric oxide (NO) bioavailability and an excess production of the superoxide anion (O(2)(-)) in the stroke prone spontaneously hypertensive rat (SHRSP) compared to the normotensive Wistar Kyoto (WKY) strain. This present study has investigated whether adenoviral-mediated gene transfer of human eNOS or Cu/ZnSOD can alter the NO/O(2)(-) balance, thereby improving endothelial function.

METHODS

A recombinant adenovirus, Ad/Hu/eNOS, containing the human eNOS cDNA fragment was generated by homologous recombination in 293 cells. Ad/Hu/eNOS or Ad/Cu/ZnSOD was delivered into SHRSP carotid arteries in vivo, using a titre of 2x10(9)-2x10(10) plaque forming units (pfu)/ml, and the effect on gene expression was observed 24 h later.

RESULTS

Western blotting confirmed increased enzyme levels of eNOS and Cu/ZnSOD in the viral-infused vessels. Ex vivo, the pressor response to phenylephrine (PE) in the presence of L-NAME was increased in the eNOS-infused arteries relative to the contralateral controls, indicating restoration of basal NO availability to that observed in untreated control WKY rats. Infusion of the SOD virus produced a statistically insignificant increase in NO bioavailability.

CONCLUSIONS

Our results support our previous findings obtained using a bovine eNOS recombinant adenovirus, that recombinant adenoviral gene transfer of human eNOS has a significant effect on NO bioavailability. In contrast, AdCu/ZnSOD gene transfer does not elicit an effect in our model. These results indicate that short-term overexpression of a recombinant eNOS, but not Cu/ZnSOD gene, in carotid arteries of the SHRSP is an effective means of locally increasing NO bioavailability to improve endothelial function.

Investigation into the sources of superoxide in human blood vessels: angiotensin II increases superoxide production in human internal mammary arteries

BACKGROUND

Increased vascular superoxide anion (.O(2)(-)) production contributes to endothelial dysfunction and hypertension in animal models of cardiovascular disease. Observations in experimental animals suggest that angiotensin II (Ang II) increases.O(2)(-) production by activation of vascular NAD(P)H oxidase. We studied the sources of.O(2)(-) production in human blood vessels and investigated whether, and by what mechanism, Ang II might alter vascular.O(2)(-) production.

METHODS AND RESULTS

Internal mammary arteries (IMAs) and saphenous veins (SVs) were collected at the time of cardiac surgery. Vessels were incubated in Krebs buffer at 37 degrees C.O(2)(-) was measured by lucigenin chemiluminescence. Basal. O(2)(-) concentrations were greater in IMAs than SVs. Inhibitors of NAD(P)H oxidase (10 micromol/L to 200 micromol/L diphenyleneiodonium) and xanthine oxidase (1 mmol/L allopurinol) caused reductions in.O(2)(-) concentrations in both IMAs and SVs. Western blotting of superoxide dismutase proteins demonstrated similar expression in IMAs and SVs. Vessels were also incubated in the presence or absence of Ang II (1 pmol/L to 1 micromol/L). Ang II increased.O(2)(-) production in IMAs at 4 hours of incubation (control, 978+/-117 pmol. min(-1). mg(-1); 1 micromol/L of Ang II, 1690+/-213 pmol. min(-1). mg(-1); n=27, P=0.0001, 95% CI 336, 925) but not in SVs. This effect was completely inhibited by coincubation of IMAs with DPI (100 micromol/L), a nonspecific Ang II antagonist ([sar(1), thre(8)]-Ang II, 1 micromol/L) and a specific Ang II type 1 (AT(1)) receptor antagonist (losartan, 1 micromol/L). Conclusions-. O(2)(-) production is greater in human IMAs than in SVs. NAD(P)H oxidase and xanthine oxidase are sources of.O(2)(-) production in these vessels. The vasoactive peptide Ang II increases.O(2)(-) production in human arteries by an AT(1) receptor-dependent mechanism.

Genes and hypertension: from gene mapping in experimental models to vascular gene transfer strategies

Human essential hypertension is a complex, multifactorial, quantitative trait under a polygenic control. Several strategies have been developed over the last decade to dissect genetic determinants of hypertension. Of these, the most successful have been studies that identified rare mendelian syndromes in which a single gene mutation causes high blood pressure. The attempts to identify multiple genes, each with a small contribution to the common polygenic form of hypertension, have been less successful. Several laboratories focused their attention on rat models of genetic hypertension, which can be considered as a reductionist paradigm for human disease. Using numerous crosses between hypertensive and normotensive strains, investigators identified several quantitative trait loci (QTL) for blood pressure subphenotypes and for cardiovascular complications such as left ventricular hypertrophy, kidney failure, stroke, and insulin resistance. Furthermore, congenic strains have been produced to confirm the existence of some of these QTL and to narrow down the chromosomal regions of interest. A number of interesting strategies have been developed, including a "speed" congenic strategy perfected by our group in Glasgow. However, the limit of congenic strategy is estimated at 1 cM, which corresponds to 2x10(6) base pairs of DNA and approximately 50 candidate genes. It is envisaged that gene expression profiling with cDNA microarrays might allow a quick progression toward the gene identification within cardiovascular QTL. In parallel experimental effort, several laboratories have been developing gene transfer/therapy strategies with adenoviral or adeno-associated viral vectors used, for example, to overexpress protective vascular genes such as vascular endothelial growth factor or endothelial nitric oxide synthase. It is anticipated that further developments in positional cloning of susceptibility and severity genes in hypertension and its complications will lead to a direct transfer of these discoveries to essential hypertension in humans and will ultimately produce novel targets for local and systemic gene therapy in cardiovascular disease.

Gene transfer of endothelial nitric oxide synthase improves nitric oxide-dependent endothelial function in a hypertensive rat model

OBJECTIVE

We have shown previously that there is a relative nitric oxide deficiency at the level of vascular endothelium in the stroke-prone spontaneously hypertensive rat (SHRSP), a model of human essential hypertension, as compared to its normotensive reference strain Wistar Kyoto (WKY) rat. The aim of the current study was to investigate whether adenoviral-mediated gene transfer of an endothelial nitric oxide synthase (eNOS) cDNA (AdCMVeNOS) into carotid arteries of the SHRSP may improve endothelial function.

METHODS

Enzyme activity of the recombinant eNOS protein encoded by AdCMVeNOS was tested using a Griess assay in endothelial cells in culture. Left carotid arteries of SHRSP were surgically isolated and exposed to either the AdCMVeNOS or control beta-galactosidase-containing virus, (2 x 10(9) pfu/ml) ex vivo and in vivo. The vessels were harvested 24 h after surgery and analysed by Western blotting, immunohistochemistry and by examining endothelial function ex vivo.

RESULTS

Cultured endothelial cells showed almost 100% transduction with both viruses and a dose response of eNOS expression showed a five-fold increase in nitrite production for AdCMVeNOS with no change for beta-galactosidase-containing virus. Western blotting demonstrated a significant increase of eNOS expression in vessels infused with AdCMVeNOS when compared to controls. Immunohistochemistry showed highly positive staining with monoclonal antibodies against eNOS in the intact endothelial cells of the AdCMVeNOS infused vessels. The areas under the curve of the concentration responses to phenylephrine (10(-9) to 3 x 10(-6) M) in the absence and presence of NG-nitroarginine methyl ester (100 microM) showed increased basal nitric oxide bioavailability in the carotid arteries infused with AdCMVeNOS compared to the control (n = 6 for each; P = 0.0069; 95% CI, 0.864 to 3.277).

CONCLUSIONS

Our results show that AdCMVeNOS is an effective tool for vascular gene transfer and that it can improve endothelial NO availability in the SHRSP, a genetic model of essential hypertension and endothelial dysfunction.

Different effects of antihypertensive agents on cardiac and vascular hypertrophy in the transgenic rat line TGR(mRen2)27

The hypertensive transgenic rat model TGR(mRen2)27 has been used to investigate the development of cardiac and vascular hypertrophy in response to two different drug regimes. Cardiac hypertrophy was shown to be related to age and gender with the copy number of mouse renin transgenes having an additive effect. A similar observation was noted for hypertrophy in the vasculature, which was assessed using flow cytometry cell cycle DNA analysis of aortic vascular smooth muscle cells. Chronic treatment from weaning with equihypotensive doses of perindopril (2 mg/kg/day) or hydralazine and hydrochlorothiazide (4 mg/day of each) prevented the development of cardiac hypertrophy. Perindopril treatment also effectively prevented the development of vascular hypertrophy; however, treatment with hydralazine and hydrochlorothiazide was not as effective despite equivalent blood pressure reduction. These studies have demonstrated the presence of marked vascular and cardiac hypertrophy in the hypertensive transgenic TGR(mRen2)27 model of hypertension. Furthermore, these results provide new evidence to support the role of a locally activated renin angiotensin system in the blood vessel wall, which is involved in the pathogenesis of vascular hypertrophy in this transgenic rat model.

Superoxide anion production is increased in a model of genetic hypertension: role of the endothelium

The hypothesis that the decreased nitric oxide (NO) availability observed in spontaneously hypertensive stroke-prone rats (SHRSP) is due to excess superoxide (O2-) was examined. O2- generation, measured by lucigenin chemiluminescence, was studied in 12- to 16-week male and female Wistar-Kyoto rats (WKY) and SHRSP. In addition, expression of the gene encoding endothelial NO synthase, the enzyme involved in NO generation, was investigated. O2- generation was increased in male and female SHRSP (4.11+/-0.24 and 3. 84+/-0.28 nmol O2-. min-1. mg-1 respectively) compared with their WKY counterparts and was significantly higher in male than female WKY (1.22+/-0.08 in males and 0.8+/-0.08 nmol O2-. min-1. mg-1 respectively) (SHRSP versus WKY P<0.0001, 95% CI -3.39, -2.51; male versus female WKY P=0.0029, 95% CI -0.67, -0.17). Removal of the endothelium by rubbing or addition of NO synthase inhibitors attenuated O2- generation in SHRSP but not WKY. In males, removal of the endothelium reduced O2- generation from 3.86+/-0.12 to 1.35+/-0. 08 nmol. min-1. mg-1 (P<0.0001, 95% CI 2.29, 2.81), whereas addition of L-NAME caused a reduction from 4.13+/-0.17 to 1.32+/-0.16 nmol. min-1. mg-1 (P<0.0001, 95% CI 2.36, 2.83). Similar reductions were observed in females. L-arginine had no significant effect, but tetrahydrobiopterin significantly decreased O2- generation in SHRSP from 4.04+/-0.11 to 2.36+/-0.40 nmol. min-1. mg-1 (P=0.0026, 95% CI 0.89, 2.44). Endothelial NO synthase mRNA expression was significantly greater in SHRSP than in WKY and in WKY males than in WKY females. These results show that O2- generation is increased in SHRSP and that the tissue and enzymatic sources of this excess O2- appear to be the endothelium and eNOS, respectively. The increase in O2- generation could explain the decreased availability of basal NO observed in this model of genetic hypertension.

Genes encoding atrial and brain natriuretic peptides as candidates for sensitivity to brain ischemia in stroke-prone hypertensive rats

-Previous studies suggested that atrial natriuretic peptide gene (Anp) and brain natriuretic peptide gene (Bnp) are plausible candidate genes for susceptibility to stroke and for sensitivity to brain ischemia in the stroke-prone spontaneously hypertensive rat (SHRSP). We performed structural and functional analyses of these 2 genes in SHRSP from Glasgow colonies (SHRSPGla) and Wistar-Kyoto rats from Glasgow colonies (WKYGla) and developed a radiation hybrid map of the relevant region of rat chromosome 5. Sequencing of the coding regions of the Anp and Bnp genes revealed no difference between the 2 strains. Expression studies in brain tissue showed no differences at baseline and at 24 hours after middle cerebral artery occlusion. Plasma concentrations of atrial natriuretic peptide (ANP) did not differ between the SHRSPGla and WKYGla, whereas concentrations of brain natriuretic peptide were significantly higher in the SHRSPGla as compared with the WKYGla (n=11 to 14; 163+/-21 pg/mL and 78+/-14 pg/mL; 95% confidence interval 31 to 138, P=0.003). We did not detect any attenuation of endothelium-dependent relaxations to bradykinin or ANP in middle cerebral arteries from the SHRSPGla; indeed the sensitivity to ANP was significantly increased in arteries harvested from this strain (WKYGla: n=8; pD2=7. 3+/-0.2 and SHRSPGla: n=8; pD2=8.2+/-0.15; P<0.01). Moreover, radiation hybrid mapping and fluorescence in situ hybridization allowed us to map the Anf marker in the telomeric position of rat chromosome 5 in close proximity to D5Rat48, D5Rat47, D5Mgh15, and D5Mgh16. These results exclude Anp and Bnp as candidate genes for the sensitivity to brain ischemia and pave the way to further congenic and physical mapping strategies.

Genetics of experimental hypertension

Experimental models of genetic hypertension are used to develop paradigms to study human essential hypertension while removing some of the complexity inherent in the study of human subjects. Since 1991 several quantitative trait loci responsible for blood pressure regulation have been identified in various rat crosses. More recently, a series of interesting quantitative trait loci influencing cardiac hypertrophy, stroke, metabolic syndrome and renal damage has also been described. It is recognized that the identification of large chromosomal regions containing a quantitative trait locus is only a first step towards gene identification. The next step is the production of congenic strains and substrains to confirm the existence of the quantitative trait locus and to narrow down the chromosomal region of interest. Several congenic strains have already been produced, with further refinement of the methodology currently in progress. The ultimate goal is to achieve positional cloning of the causal gene, a task which has so far been elusive. There are several areas of cross-fertilization between experimental and human genetics of hypertension, with a successful transfer of two loci directly from rats to humans and with new pharmacogenetic approaches which may be utilized in both experimental and clinical settings.

Spatial ability in children's play with Lego blocks

Sex differences in spatial ability have been argued to originate from sex differences in children's play preferences. Child (30 boys and 20 girls) were asked to construct a specific three-dimensional model using Lego blocks and were also given the Shepard and Metzler test of mental rotation. Those who completed the Lego model scored significantly higher in spatial ability than those who did not. Constructional ability was also related to errors made during the construction of the model, but spatial ability was the best predictor of completion of the model.

The implications for academic attainment of perceived gender-appropriateness upon spatial task performance

BACKGROUND

Male superiority in spatial ability has traditionally been used as an explanation for the male domination of 'spatial' disciplines such as mathematics, science and computing. Data are presented which show the degree of male domination of these disciplines at a range of academic levels.

AIMS

To evaluate the effect of describing a spatial ability test either as a measure of spatial ability (traditional format) or as a measure of empathy, upon male and female performance. Psychological gender is also assessed to evaluate the role of masculinity and femininity upon performance.

METHOD

Eighty-four sixth form students were presented with the Group Embedded Figures Test in the assessment's traditional format and as a measure of 'empathy'. Levels of masculinity and femininity were also assessed using the Bem Sex Role Inventory.

RESULTS

Whilst the description of the nature of the assessment did not affect male performance, female performance' varied significantly as a function of test description. Females only underperformed when the test was described as a measure of spatial ability. Additionally, those high in masculinity were found to outperform those high in femininity.

CONCLUSIONS

The results suggest that 'apparent' sex differences in spatial ability are more accurately described as psychological gender differences which determine the motivation to attempt the assessments.

COMMENT

The implications for genderised activities (such as computing) within education are discussed.

Left ventricular hypertrophy and arterial blood pressure in experimental models of hypertension

Cardiac hypertrophy in essential and experimental (genetic) hypertension have been initially attributed to increased pressure load. However, the level of blood pressure does not parallel the degree of cardiac hypertrophy, i.e., a complex relationship rather than a simple dose-response effect has to be suggested. Several non-haemodynamic factors which influence LV mass have been identified with genetic and neuro-hormonal influences playing a major role. The experimental strategies which have been used to highlight one or more of these influences include pharmacological studies of regression or prevention of LVH and studies designed to produce LVH de-novo in normotensive strains. All these studies while confirming an important role of haemodynamic factors also stress the major influence of the renin-angiotensin system and the inter-relationship between angiotensin II and nitric oxide. In contrast, genetic strategies, from simple co-segregation analysis to most complex genome scan studies, suggest the existence of "susceptibility genes" for LV hypertrophy, a finding which deserves further study in large collections of siblings and family groups with essential hypertension.

Vascular smooth muscle cell polyploidy and cardiomyocyte hypertrophy due to chronic NOS inhibition in vivo

To assess the vascular and cardiac response to NO (nitric oxide) synthase (NOS) blockade in vivo, Wistar-Kyoto rats (WKY) were treated for 3 wk with NG-nitro-L-arginine methyl ester (L-NAME; 10 mg.kg-1.day-1). L-NAME treatment induced hypertension that was associated with increased plasma renin activity. Flow cytometry cell cycle DNA analysis showed that aortic vascular smooth muscle cells (VSMC) from L-NAME-treated WKY had a significantly higher polyploid population compared with WKY controls. Using organ bath experiments, we have shown that aortic rings from L-NAME-treated WKY have an increased contractile response to phenylephrine and impaired relaxation to carbachol compared with control rings. NOS blockade in vivo caused a significant increase in cardiac and left ventricular hypertrophy. Northern mRNA analysis of the myocardium showed that L-NAME treatment caused reexpression of the fetal skeletal alpha-actin isoform without alterations in collagen type I expression, a pattern indicating true hypertrophy of the cardiomyocytes. These studies provide further insight to confirm that NO deficiency in vivo results in the development of vascular and cardiac hypertrophy.

Sensitivity to cerebral ischaemic insult in a rat model of stroke is determined by a single genetic locus

Ischaemic stroke is a complex disorder caused by a combination of genetic and environmental factors. Clinical and epidemiological studies have provided strong evidence for genetic influences in the development of human stroke and several mendelian traits featuring stroke have been described. The genetic analysis of the non-mendelian, common ischaemic stroke in humans is hindered by the late onset of the disease and the mode of inheritance, which is complex, polygenic and multifactorial. An important approach to the study of such polygenic diseases is the use of appropriate animal models in which individual contributing factors can be recognized and analysed. The spontaneously hypertensive stroke-prone rat (SHRSP) is an experimental model of stroke characterized by a high frequency of spontaneous strokes as well as an increased sensitivity to experimentally induced focal cerebral ischaemia. Rubattu et al. performed a genomewide screen in an F2 cross obtained by mating SHRSP and SHR, in which latency to stroke on Japanese rat diet was used as a phenotype. This study identified three major quantitative trait loci (QTLs), STR-1-3. Of these, STR-2 and 3 conferred a protective effect against stroke in the presence of SHRSP alleles and STR-2 co-localized with the genes encoding for atrial natriuretic and brain natriuretic factors. Our investigation was designed to identify the genetic component responsible for large infarct volumes in the SHRSP in response to a focal ischaemic insult by performance of a genome scan in an F2 cross derived from the SHRSP and the normotensive reference strain, WKY rat. We identified a highly significant QTL on rat chromosome 5 with a lod score of 16.6 which accounts for 67% of the total variance, co-localizes with the genes encoding atrial and brain natriuretic factor and is blood pressure independent.

Quantitative trait loci in genetically hypertensive rats. Possible sex specificity

We performed a total genome screen in an F2 cross derived from the stroke-prone spontaneously hypertensive rat and the normotensive Wistar-Kyoto rat. Blood pressure at baseline and after 1% NaCl was measured by radiotelemetry; other phenotypes included heart rate, motor activity, left ventricle weight to body weight ratio, and vascular smooth muscle cell polyploidy, a measure of vascular hypertrophy. Quantitative trait loci affecting a given phenotype were mapped relative to microsatellite markers by using the MAPMAKER/QTL 1.1 computer package. We identified three blood pressure quantitative trait loci, two on rat chromosome 2 and one on rat chromosome 3. The quantitative trait loci close to genetic markers D2Mgh12 ("suggestive" linkage, with a maximal logarithm of the odds [LOD] score of 3.1) and D3Mgh16 (significant linkage, with a maximal LOD score of 5.6) showed possible sex specificity in the male F2 cohort only. This was confirmed by the likelihood ratio test for the difference in locus effects between the sexes. We also identified a new quantitative trait locus for LV hypertrophy on rat chromosome 14 ("suggestive" linkage, with a maximal LOD score of 3.1). The sex specificity of blood pressure quantitative trait loci will be important in designing congenic strains and substrains for fine genetic mapping and for identifying genes that regulate blood pressure.

Altering creatine kinase isoenzymes in transgenic mouse muscle by overexpression of the B subunit

To change the levels of expression and isoenzyme distribution of creatine kinase (CK) in muscle, transgenic technology was used to express the B subunit of CK in mouse muscle. Normally, mammalian skeletal muscle contains the MM dimer of CK. The BB dimer and MB heterodimer of CK can be found in brain and heart, respectively. Heterologous genes consisting of skeletal and cardiac muscle-specific actin promoters fused to the genomic coding region of the B form of CK were used to create transgenic mice. Lines were established from the three highest expressing founders. Analysis of skeletal muscle extracts revealed that all three lines had an increase in total CK activity measured under maximal velocity conditions. The highest expressing line, 7001, had a CK activity 150% that of control muscle. Nuclear magnetic resonance saturation transfer was used to measure the in vivo rate of the CK reaction. In 7001 hindlimb muscles, the CK catalyzed reaction was 200% that of control muscle. The elevation in CK activity in transgenic muscle was accompanied by significant changes in the composition of the cytosolic isoenzyme ratio of CK. In control, 100% of CK was MM, whereas 7001 had 60 +/- 18% MM, 32 +/- 10% MB, and 8 +/- 2% BB. There were no changes in ATP, phosphocreatine, Pi, or creatine levels in transgenic muscle compared with control. Immunofluorescence of myofibrils isolated from control and transgenic muscle revealed specific association of CK to the M line. Small amounts of MB CK were detected on myofibrils from transgenic mice. Transgenic mice expressing the B subunit of CK in muscle represent a first step toward altering CK isoforms so as to elucidate the specific roles of these isoforms in energy metabolism.

Phosphocreatine protects ATP from a fructose load in transgenic mouse liver expressing creatine kinase

The effects of an intraperitoneal dose of fructose on hepatic metabolism in transgenic mice expressing creatine kinase in liver were investigated using phosphorus-31 nuclear magnetic resonance (31P-NMR). Transgenic mice were fed diets containing varying amounts of creatine (Cr; 0-12%). It has previously been shown that 31P-NMR spectra of transgenic mice have a peak due to phosphocreatine (PCr), the intensity of which was proportional to the amount of Cr in the diet. No PCr peak was detected in control mice or transgenic mice not fed Cr. In the present study NMR spectra were collected before and for a 1-h recovery period after infusion of 0.15 mmol/10 g body wt fructose. In all mice infusion of fructose resulted in a two- to threefold elevation of phosphomonoesters. In control and non-Cr-fed transgenic mice this was accompanied by a 60% reduction of the inorganic phosphate (Pi) and a 50% fall in ATP. In transgenic mice fed Cr, the extent of reduction of Pi was dependent on the level of PCr and was markedly reduced compared with controls. Falls in Pi of 46, 24, and 6% were detected 12.5 min after fructose infusion in low, intermediate, and high PCr-containing livers, respectively. The presence of PCr also protected hepatic ATP levels from a fructose load. Transgenic mice fed on high or intermediate Cr diets showed no significant loss of ATP. However, livers with low levels of PCr lost ATP during a fructose challenge. From the equilibrium established by creatine kinase, free ADP levels were calculated throughout the fructose dose. Fructose caused a 2.5-fold increase in free ADP. This rise in ADP was independent of the total Cr or whether Pi and ATP were reduced by fructose infusion. These results indicate that an increase in ADP is not sufficient to cause depletion of ATP during a fructose challenge.

Free ADP levels in transgenic mouse liver expressing creatine kinase. Effects of enzyme activity, phosphagen type, and substrate concentration

ADP is an important regulator of hepatic metabolism. Despite its importance the level of free ADP in the liver remains controversial. Recently, we engineered transgenic mice which express high levels of creatine kinase in liver. The reaction catalyzed by creatine kinase was assumed to be at equilibrium and used to calculate a free ADP level of 0.059 mumol/g wet weight. In this report we test the equilibrium assumption by studying the free ADP level as a function of enzyme activity or substrate content. Over a 5-fold range of creatine kinase activity, from 150-800 mumol/min/g wet weight, there was no change in the free ADP level. The average value of ADP for these mice was 0.061 +/- 0.016 mumol/g wet weight. Similarly, altering hepatic creatine content from 1.6 to 30 mumol/g wet weight had no effect on the calculated total free ADP level. The average value of ADP for the creatine levels was 0.048 +/- 0.015 mumol/g wet weight. Finally, the free ADP level was calculated using the equilibrium with cyclocreatine rather than creatine as substrate. The equilibrium of the reaction with cyclocreatine lies 30 times more toward phosphorylation than does the equilibrium with creatine. A free ADP level of 0.063 +/- 0.031 mumol/g wet weight was calculated using cyclocreatine. This value is not different from that found with creatine. These results show that the equilibrium assumption used to calculate free ADP levels in transgenic mouse liver is valid, and the presence of creatine kinase does not affect ADP levels.

NMR detection of creatine kinase expressed in liver of transgenic mice: determination of free ADP levels

To use the equilibrium established by creatine kinase (CK) to determine hepatic free ADP levels, the transcriptional control elements of the transthyretin gene were used to direct expression of the CK B isozyme to the livers of transgenic mice. Activities of CK ranging from 80-250 mumol per min per g (wet weight) were detected in liver extracts from five founder mice. The CK activity was stably transmitted to subsequent generations. Isozyme gels and immunoblots confirmed that the activity detected in extracts was due to the B isozyme of CK. Immunohistology indicated that the protein was expressed uniformly throughout the liver and was localized primarily to the cytoplasm. 31P NMR spectroscopy was used to detect the metabolic product of the CK reaction, phosphocreatine, demonstrating that the enzyme was active in vivo. The phosphocreatine level fell rapidly during anoxia (t1/2 = 1 min), indicating that the CK reaction was integrated into hepatic energy metabolism. The equilibrium established by CK was used to calculate a hepatic free ADP level of 0.059 +/- 0.004 mumol/g (wet weight). In vivo NMR studies of these mice will be valuable for studying the role of free ADP in regulating liver metabolism.

Ca2+-ATPase deficiency in a patient with an exertional muscle pain syndrome

31P Magnetic resonance spectroscopy studies were carried out in vivo on skeletal muscle of a patient with verapamil-responsive, chronic, progressive post-exertional muscle pain. A sister suffered from a similar complaint. The results showed that the muscle: (1) decreased its high energy phosphate content more rapidly than normal during exercise, indicating either increased utilisation or decreased production of ATP; (2) acidified more rapidly than normal during exercise suggesting an increased glycolytic rate; (3) continued in some studies to acidify markedly during the first minute after exercise, indicating that glycolysis remained active into the recovery period; (4) had phosphocreatine and ADP recovery rates consistent with normal rates of oxidative phosphorylation. On the basis of these results, it was proposed that the patient suffers from a defect in Ca2+ handling in the muscle. Subsequently, direct measurement of Ca2+-ATPase activity in the sarcoplasmic reticulum fraction from a muscle biopsy sample showed that the activity of this enzyme was reduced by about 90%.

An animal model of mitochondrial myopathy: a biochemical and physiological investigation of rats treated in vivo with the NADH-CoQ reductase inhibitor, diphenyleneiodonium

Chronic administration of the NADH-CoQ reductase inhibitor, diphenyleneiodonium to rats at two dose levels, 1.0 and 1.5 mg/kg per day, caused a 40% and 60% reduction, respectively, in the in vitro rate of NAD-linked respiration by skeletal muscle mitochondria. At the highest dose, muscle fatigue, lactic acidosis and an over-utilization of phosphocreatine was observed in the gastrocnemius muscle during mild stimulation of 1 Hz frequency. The resynthesis of phosphocreatine following muscle stimulation was about 2 fold slower in the treated animal group. At the low dose, no significant biochemical changes were observed during muscle stimulation at 4 Hz. The results are discussed in terms of skeletal muscle "oxidative reserve", twitch tension maintenance and the relevance to the human diseased state of mitochondrial myopathy.