Effects of long-term treatment with trandolapril on augmented vasoconstriction in rats with chronic heart failure

Comparison of high- versus low-tissue affinity ACE-inhibitor treatment on circulating aldosterone levels in patients with chronic heart failure

Introduction. Previous animal studies of chronic heart failure (CHF) suggest that angiotensin-converting enzyme (ACE) inhibitors of differing tissue avidity provide varying levels of renin-angiotensin system (RAS) suppression. Human studies have not consistently confirmed these animal findings. We hypothesised that production of circulating aldosterone (ALDO) would be suppressed to a greater extent in subjects treated with an ACE-inhibitor of higher tissue avidity. We randomised subjects with stable CHF to receive the low-tissue affinity ACE-inhibitor enalapril (ENAL) or the high-tissue affinity ACE-inhibitor trandolapril (TRAN), and assessed circulating ALDO levels at baseline and after eight weeks of treatment.

Methods. Thirty clinically stable subjects with CHF and left ventricular ejection fraction (LVEF ) < 40% who were in a steady-state fluid balance were enrolled into a prospective, randomised double-blind trial. After a one month run-in period for standardisation to initial ACE-inhibition with ENAL, baseline circulating ALDO levels were measured and patients were randomised to receive ENAL 40 mg versus O TRAN 4 mg (or the maximally tolerated doses) for eight weeks. Final determination of ALDO levels were made at the end of the 8-week study period.

Results. Baseline clinical characteristics including age, diabetes, LVEF, serum sodium, potassium and creatinine concentrations, and background medications were similar in both groups. We found no statistically significant difference in circulating ALDO levels between the ENAL and TRAN groups at the end of the 8-week study period. [ENAL (12.6 vs. 13.3 ng/dL);TRAN (12.5 vs. 14.5 ng/dL);p=NS].

Conclusion. We found no statistically significant difference in circulating ALDO levels between high- and low-tissue affinity ACE-inhibitor therapy. Further studies assessing ALDO production at the tissue level is warranted.

Increased vascular angiotensin II binding capacity and ET-1 release in young cardiomyopathic hamsters

Heart failure (HF) is a multifactorial and progressive disease that has been associated with multiple systemic and vascular alterations. Previous reports from our laboratory showed that in 2-month-old Bio-To2 Syrian cardiomyopathic hamsters (SCH) that have not yet developed the clinical manifestations of HF, the vascular contractility induced by 0.1 microM angiotensin II was approximately 35% greater than in control animals. This finding was observed concomitantly with an increased aortic ACE activity. To further evaluate the mechanisms underlying angiotensin II-enhanced vascular contraction, concentration-response curves for angiotensin II (0.01 nM-10 microM) were constructed before and after the addition of prazosin (alpha-1 blocker), NS-398 (selective COX-2 blocker) and BQ-123 (ET-1A-receptor antagonist) in aortic rings from 2-month-old SCH. The binding capacity and affinity of the AT-1 receptors were also evaluated in aortic homogenates using 125I-angiotensin II. Age-matched golden hamsters were used as controls (CT). Our results indicate that incubation with either 10 microM prazosin or 10 microM NS-398 did not modify EC50 or Emax values for angiotensin II indicating that norepinephrine and prostaglandins are not involved in the enhanced contractile action of angiotensin II. However, 10 microM BQ-123 reduced by 40% the contraction induced by 1.0 microM angiotensin II (from 1.05+/-0.04 to 0.6475+/-0.06 g/mg tissue, n = 5, P < 0.05), suggesting that in cardiomyopathic hamsters, the action of angiotensin II is mediated in part by ET-1. At lower angiotensin II concentration (0.1 microM), the ET-1-dependent contraction decreases to 29%. In addition, although dissociation constants for labeled angiotensin II were found to be similar in the aorta of SCH and control animals (K(D): CT = 7.8 nM and SCH = 5.1 nM), 125I-angiotensin II binding capacity was about 2-fold greater in SCH than in controls (Bmax: SCH = 1113 and CT = 605 fmol/mg protein). Altogether these results suggest that in 2-month-old SCH the enhanced response of angiotensin II in the vasculature is mediated both by an increased binding capacity for the hormone and facilitation of the ET-1 action.

Decreased facilitation by angiotensin II of noradrenergic neurotransmission in isolated mesenteric artery of rabbits with chronic heart failure

Both in human and in experimental heart failure (HF), the renin-angiotensin system and the sympathetic nervous system are activated. In a previous study a facilitatory action of angiotensin II (Ang II) was shown in the rabbit mesenteric artery, which was mediated via prejunctionally located Ang II type 1 (AT ) receptors. Very little is known about the effects of Ang II on sympathetic neurotransmission at the peripheral level in congestive heart failure (CFH). Accordingly, in the isolated mesenteric arteries obtained from rabbits with experimentally induced CHF, as well as in age-matched control rabbits, the effect of Ang II on contractions provoked by electrical field stimulation was investigated in the presence and absence of the AT receptor antagonist eprosartan. Additionally, to investigate a possible postjunctional facilitation, the effects of Ang II on alpha-adrenoceptor-mediated responses were studied using noradrenaline (NA). Lastly, the vasoconstrictor effects of Ang II were compared between HF rabbits and controls, by constructing concentration-response curves to Ang II. In control rabbits, Ang II 0.5 n caused an enhancement of stimulation-induced responses by a factor 3.2 +/- 0.5, 2.4 +/- 0.3, and 1.5 +/- 0.08, at 1, 2, and 4 Hz, respectively ( < 0.05 at all frequencies compared with vehicle). In rabbits with HF, the enhancement by Ang II (0.5 n ) amounted to a factor 2.1 +/- 0.2, 1.7 +/- 0.1, and 1.2 +/- 0.04, at 1, 2, and 4 Hz, respectively ( < 0.05 compared with vehicle at all frequencies). Accordingly, the enhancing effect of Ang II was more pronounced in the control group compared with rabbits with HF ( < 0.05 at each frequency). Eprosartan (1 nM -0.1 microM) could inhibit the facilitatory effects of Ang II in arteries from HF as well as from control rabbits. Contractile responses to exogenous NA (3 n -0.1 m ) were the same in HF rabbits and controls, and they were unaltered in the presence of Ang II 0.5 n Ang II (0.1 nM -1 microM) caused a concentration-dependent increase in contractile force, which was the same in HF rabbits and controls. From these findings it can be concluded that in rabbits with CHF as well as in control animals, Ang II facilitates the stimulation-induced vasoconstrictor responses via prejunctionally located AT receptors. The facilitating effect was decreased in vessels obtained from rabbits with CHF, whereas responses to exogenous Ang II were unchanged. These findings may be explained by downregulation or uncoupling of the prejunctional AT receptor.