Evaluation of renal causes of hypertension

Non-enhanced MR angiography of renal arteries: comparison with contrast-enhanced MR angiography

BACKGROUND

The main causes of renal artery stenosis (RAS) are atherosclerosis and fibromuscular dysplasia. Despite contrast-enhanced magnetic resonance angiography (CE-MRA) being a safe and reliable method for diagnosis of RAS especially in young individuals, recently it has been possible to adopt innovative technologies that do not require paramagnetic contrast agents.

PURPOSE

To assess the accuracy of steady-state free-precession (SSFP) non-contrast-enhanced magnetic resonance angiography (NC-MRA) by using a 1.5 T MR scanner for the detection of renal artery stenosis, in comparison with breath-hold CE-MRA as the reference standard.

MATERIAL AND METHODS

Sixty-three patients (33 men, 30 women) with suspected renovascular hypertension (RVHT) were examined by a 1.5T MR scanner; NC-MRA with an electrocardiography (ECG)-gated SSFP sequence was performed in 58.7% (37/63) of patients; in 41.3% (26/63) of patients a respiratory trigger was used in addition to cardiac gating. CE-MRA, with a three-dimensional gradient echo (3D-GRE) T1-weighted sequence, was performed in all patients within the same session. Maximum intensity projection (MIP) image quality, number of renal arteries, and the presence of stenosis were assessed by two observers (independently for NC-MRA and together for CE-MRA). The agreement between NC-MRA and CE-MRA as well as the inter-observer reproducibility were calculated with Bland-Altman plots.

RESULTS

MIP image quality was considered better for NC-MRA. NC-MRA identified 143 of 144 (99.3%) arteries detected by CE-MRA (an accessory artery was not identified). Fourteen stenoses were detected by CE-MRA (11 atherosclerotic, 3 dysplastic) with four of 14 (28.5%) significant stenosis. Bland-Altman plot demonstrated an excellent concordance between NC-MRA and CE-MRA; particularly, the reader A evaluated correctly all investigated arteries, while over-estimation of two stenoses occurred for reader B. Regarding NC-MRA, inter-observer agreement was excellent.

CONCLUSION

NC-MRA is a valid alternative to CE-MRA for the assessment of renal arteries.

The dopamine D3 receptor knockout mouse mimics aging-related changes in autonomic function and cardiac fibrosis

Blood pressure increases with age, and dysfunction of the dopamine D3 receptor has been implicated in the pathogenesis of hypertension. To evaluate the role of the D3 receptor in aging-related hypertension, we assessed cardiac structure and function in differently aged (2 mo, 1 yr, 2 yr) wild type (WT) and young (2 mo) D3 receptor knockout mice (D3KO). In WT, systolic and diastolic blood pressures and rate-pressure product (RPP) significantly increased with age, while heart rate significantly decreased. Blood pressure values, heart rate and RPP of young D3KO were significantly elevated over age-matched WT, but similar to those of the 2 yr old WT. Echocardiography revealed that the functional measurements of ejection fraction and fractional shortening decreased significantly with age in WT and that they were significantly smaller in D3KO compared to young WT. Despite this functional change however, cardiac morphology remained similar between the age-matched WT and D3KO. Additional morphometric analyses confirmed an aging-related increase in left ventricle (LV) and myocyte cross-sectional areas in WT, but found no difference between age-matched young WT and D3KO. In contrast, interstitial fibrosis, which increased with age in WT, was significantly elevated in the D3KO over age-matched WT, and similar to 2 yr old WT. Western analyses of myocardial homogenates revealed significantly increased levels of pro- and mature collagen type I in young D3KO. Column zymography revealed that activities of myocardial MMP-2 and MMP-9 increased with age in WTs, but in D3KO, only MMP-9 activity was significantly increased over age-matched WTs. Our data provide evidence that the dopamine D3 receptor has a critical role in the emergence of aging-related cardiac fibrosis, remodeling, and dysfunction.