Manganese kinetics demonstrated double contrast in acute but not in chronic infarction in a mouse model of myocardial occlusion reperfusion

Manganese (Mn(2+)) is considered as a specific MRI contrast agent that enters viable cardiomyocytes through calcium pathways. Compared to extracellular gadolinium based contrast agents, it has the potential to assess cell viability. To date, only information from the washout phase after recirculation has been used for the detection and characterization of myocardial infarct. This study showed for the first time that in a mouse model of coronary occlusion-reperfusion, Mn(2+) wash-in kinetics are different at 24 h after surgery (acute infarction) than at eight days after surgery (chronic infarction). A fast but transient entry of Mn(2+) into the acute infarct area led to a double contrast between infarct and remote areas, whereas entry of Mn(2+) into the chronic infarct area remained reduced compared to remote regions during both wash-in and washout phases. The main hypothesis is that extracellular space is largely enhanced in acute infarction due to cell membrane rupture and interstitial edema, whereas scar tissue is densely composed of collagen fibers that reduce the distribution volume of free Mn(2+) ions. In addition to its ability to accurately depict the infarct area during the redistribution phase, Mn(2+) is also able to discriminate acute versus chronic injury by the observation of double-contrast kinetics in a mouse model of ischemia reperfusion.

Physiopathology of the embryonic heart (with special emphasis on hypoxia and reoxygenation)

The adaptative response of the developing heart to adverse intrauterine environment such as reduced O2 delivery can result in alteration of gene expression with short- and long-term consequences including adult cardiovascular diseases. The tolerance of the developing heart of acute or chronic oxygen deprivation, its capacity to recover during reperfusion and the mechanisms involved in reoxygenation injury are still under debate. Indeed, the pattern of response of the immature myocardium to hypoxia-reoxygenation differs from that of the adult. This review deals with the structural and metabolic characteristics of the embryonic heart and the functional consequences of hypoxia and reoxygenation. The relative contribution of calcium and sodium overload, pH disturbances and oxidant stress to the hypoxia-induced cardiac dysfunction is examined, as well as various cellular signaling pathways (e.g. MAP kinases) involved in cell survival or death. In the context of the recent advances in developmental cardiology and fetal cardiac surgery, a better understanding of the physiopathology of the stressed developing heart is required.

Significance of urinary angiotensinogen in essential hypertension as a function of plasma renin and aldosterone status

OBJECTIVE

This study was performed to test the significance of urinary angiotensinogen (UAGT) in essential hypertensive patients stratified as a function of plasma renin and aldosterone.

METHODS AND RESULTS

A sample of 248 essential hypertensives, investigated under their usual sodium diet and either off-medication or under a standardized treatment, was separated into two groups on the basis of upright plasma active renin and aldosterone medians. Patients with plasma active renin and aldosterone below medians are referred to as the low renin-aldosterone essential hypertensive group (LRA-EH). Others subjects are defined as other essential hypertensives (O-EH). Blood pressure (BP) was recorded by 24-h ambulatory monitoring. UAGT was measured by a specific enzyme-linked immunosorbent assay for total angiotensinogen. Because UAGT was markedly increased in the presence of overt proteinuria (>/= 300 mg/24 h), proteinuric patients (n = 29) were excluded from subsequent analyses. UAGT was a significant predictor of systolic and diastolic BP in LRA-EH females (P < 0.01 and P = 0.05, respectively) but not in males. By contrast, urinary sodium excretion (P < 0.001) and maintenance of treatment (P = 0.002) were significant predictors of systolic BP in males. These correlations were not observed in O-EH, whether males or females.

CONCLUSIONS

In the present study, UAGT stands as a strong predictor of BP in women with low plasma renin/aldosterone, suggesting an involvement of the tubular renin-angiotensin system in these subjects. Higher sodium intake or the need to maintain treatment may account in part for the lack of a similar relationship in males.

A1166C polymorphism of angiotensin II type 1 receptor, blood pressure and arterial stiffness in hypertension

OBJECTIVE

To study the association of the AC polymorphism of angiotensin II type 1 receptor gene (AGTR1) with blood pressure and central arterial stiffness in a population of hypertensive patients referred to hospital for further work-up.

METHODS

One hundred and eighty-five patients, referred to our department from April 1998 to February 2002, were included. Blood pressure was measured by conventional and 24-h ambulatory methods, and arterial stiffness by carotid-femoral pulse wave velocity (PWV) determination. Genotyping for the AGTR1 AC polymorphism was performed by polymerase chain reaction.

RESULTS

AGTR1 AC polymorphism was not associated with systolic or diastolic blood pressure, measured either by conventional (P=0.89 and P=0.67, respectively) or by 24-h ambulatory (P=0.57 and P=0.56, respectively) methods. Conversely, this polymorphism was significantly associated with PWV (P=0.006) and had a dose-allele effect, PWV increasing with the number of A alleles (10.6 +/- 2.4 m/s in CC, 11.9 +/- 2.5 m/s in AC and 12.7 +/- 2.7 m/s in AA patients, P=0.002). Multiple regression analysis showed that AC polymorphism was still independently associated with PWV (P=0.01) and was the third most important determinant of PWV after age (P <0.0001) and 24-h mean blood pressure (P <0.0001).

CONCLUSION

In our study population, central arterial stiffness assessed by PWV was significantly and independently associated with the AC polymorphism, increased PWV being associated with the presence of the A allele. Further investigations are required for identification of the underlying mechanisms.