Heterogeneity in morphological characteristics of coronary arteries and aortae in various models of hypertension

Early regression of coronary artery remodeling with esmolol and DDAH/ADMA pathway in hypertensive rats

Our preclinical study demonstrated that esmolol produces early regression of left ventricular hypertrophy in arterial hypertension. The aim of this study was to assess the effects of short-term esmolol therapy on the regression of left anterior descending artery remodeling in spontaneously hypertensive rats (SHRs), and to determine whether the asymmetric dimethylarginine (ADMA)/dimethylarginine dimethylaminohydrolase (DDAH) pathway, a regulator of nitric oxide (NO) bioavailability, accounted for this regression. Fourteen-month-old male SHRs were treated intravenously with vehicle (SHR, n=15) or esmolol (SHR-E, n=20) (300 μg kg^-1 min^-1). Age-matched, vehicle-treated male Wistar-Kyoto rats (WKY, n=15) served as controls. SHRs were also treated with nitroglycerin (SHR-N, n=5). After 48 h, the left anterior descending artery structure and morphology were assessed, and dose-response curves for 5-hydroxytryptamine (5-HT, 10^-9-3 × 10^-5 mol l^-1) were constructed. ADMA concentrations in plasma and left ventricle and DDAH activity in tissue were analyzed. Wall thickness and cross-sectional area were significantly lower after treatment with esmolol in SHR-E than in SHR. Media thickness and smooth muscle cell count were lower in SHR-E than in SHR. Esmolol induced a significant reduction in adventitial cell count in SHR-E. The area under the concentration-response curves was significantly higher in SHR than in SHR-E, as were the esmolol normalized coronary artery contracting responses to 5-HT. We found significantly lower ADMA levels and significantly higher DDAH activity in the ventricle in SHR-E than in SHR. The protective effect of esmolol on the regression of left anterior descending artery remodeling may be related to the reduction in ADMA levels.

Endothelin-1-receptor-mediated responses in resistance vessels of young and adult spontaneously hypertensive rats

OBJECTIVE

To assess whether primary changes in endothelin-1 (ET-1) receptor responsiveness or secondary vessel functional modifications could characterize the effects evoked by ET-1 in the mesenteric vascular bed (MVB) of prehypertensive 5-week-old and 12-week-old spontaneously hypertensive rats (SHRs).

DESIGN AND METHODS

We used male 5-week-old and 12-week-old SHRs and sex- and age-matched Wistar-Kyoto (WKY) rats as controls. ET-1 receptor responsiveness was evaluated by ET-1 (0.04-2 micromol/l) concentration-response curves and repeated with indomethacin and BQ-123 (0.1-0.5 micromol/l), the latter a selective ETA receptor antagonist. ETB receptor responsiveness was tested by sarafotoxin S6c (1-100 nmol/l) and IRL-1620 (0.1-10 nmol/l) concentration-response curves, obtained in the noradrenaline-precontracted MVB.

RESULTS

At 5 weeks of age, ET-1 induced a similar concentration-dependent contraction in SHRs and WKY rats, with an overlapping BQ-123 pA2 value (negative common logarithm of the antagonist that produces an agonist dose ratio of 2) in the two strains. Indomethacin was ineffective in both groups. Sarafotoxin S6c and IRL-1620 both evoked an ETB-mediated, significant relaxation, only in WKY rats. In 12-week-old SHRs, ET-1 evoked a markedly increased maximal effect compared with the response in WKY rats (P< 0.01); this was prevented by treatment with indomethacin. The BQ-123 pA2 value was higher in SHRs than in WKY rats (P< 0.01). Both sarafotoxin S6c and IRL-1620 evoked a significant concentration-dependent relaxation in WKY rats, which was not detected in SHR preparations.

CONCLUSIONS

Our results could suggest that the different responses evoked by ET-1 in the MVB of SHRs during the onset of hypertension may be related partially to primary alterations in the ET-1 receptorial pattern and partially to the onset of high blood pressure, leading to an impairment in the haemodynamic balance.