Angiotensin II blockade [corrected] enhances baroreflex control of sympathetic outflow in heart failure

Recent insight into therapy of congestive heart failure: focus on ACE inhibition and angiotensin-II antagonism

One possible intervention to interrupt the deleterious effects of the renin-angiotensin system is suppression of angiotensin II (Ang II) formation by inhibition of angiotensin-converting enzyme (ACE). However, ACE inhibition incompletely suppresses Ang II formation and also leads to accumulation of bradykinin. Angiotensin II type 1 (AT1) receptors are believed to promote the known deleterious effects of Ang II. Therefore, AT1 receptor antagonists have been recently introduced into therapy for hypertension and congestive heart failure (CHF). Although there are significant differences between the effects of AT1 receptor antagonists and ACE inhibitors including the unopposed stimulation of angiotensin II type 2 (AT2) receptors by AT1 receptor antagonists, the discussion of whether ACE inhibitors, AT1 receptor antagonists or the combination of both are superior in the pharmacotherapy of CHF is still largely theoretical. Accordingly, AT1 receptor antagonists are still investigational. Angiotensin-converting enzyme inhibitors remain first line therapy in patients with CHF due to systolic dysfunction. However, in patients not able to tolerate ACE inhibitor induced side effects, in particular cough, AT1 receptor antagonism is a good alternative. In clinical practice, emphasis should be placed on increasing the utilization of ACE inhibitors, as more than 50% of patients with CHF do not receive ACE inhibitors. In addition, the majority of those on ACE inhibitors receive doses lower than the dosage used in the large clinical trials. Although not yet completely proved, it is likely that high doses of ACE inhibition are superior to low doses with respect to prognosis and symptoms.

Effect of losartan on heart rate and blood pressure variability during tilt test and trinitroglycerine vasodilation

OBJECTIVE

To define the changes in variability of heart rate and of blood pressure during vasodilation in a group of hypertensive patients treated with an angiotensin II type I (AT1) receptor inhibitor.

DESIGN

Losartan (50 mg/day at 0800 h) or placebo were administered for 3 weeks according to a single blind, crossover, randomized protocol, to 18 hypertensive patients (16 men and two women, mean age 42 + 3.6 years). Continuous ECG recording and beat-to-beat blood pressure monitoring were carried out with subjects in the supine position and during a head-up tilt test, as well as after sublingual administration of trinitroglycerine. The elaboration of ECG traces in the frequency domain, was carried out using an autoregressive method and measured using the autoregressive moving average technique.

RESULTS

Orthostatic stimulus, both during treatment with losartan and with placebo, caused a significant decrease in the heart rate high frequency power; on the other hand, the low frequency power appeared unchanged after placebo and was significantly reduced with losartan. Five minutes after the administration of trinitroglycerine, the low frequency power with placebo showed a significant increase (817 -+ 221 versus 465 + 101 ms2, P < 0.03). No change was recorded in total power nor in low frequency or high frequency power during losartan therapy. The ratio of low frequency to high frequency powers showed a sympathetic prevalence during vasodilation only during placebo treatment, whereas a mainly unchanged balance was maintained during losartan treatment Blood pressure variability showed a sympathetic prevalence after upright and trinitroglycerine stimulation only in placebo-treated subjects.

CONCLUSIONS

Our study demonstrated that vasodilation is not able to evoke an unbalancing of the autonomic modulation in hypertensive patients treated with an AT1 receptor inhibitor, but permits the maintenance of a significant vagal component, thus highlighting the favorable profile of this drug in the autonomic control of circulation.

Effects of angiotensin II on sexual function, blood pressure, and fluid intake are differentially affected by AT-1 receptor blockade

We have previously reported that third ventricular administration of angiotensin II (ANG II) immediately before mating tests suppressed copulatory behavior in male rats. The present studies examine the effects of short- (3 days) and long-term (21 days) intracerebroventricular (i.c.v.) infusion of ANG II (6 microg/h), on parameters of copulatory behavior, fluid intake, and blood pressure in sexually experienced male Long Evans rats. Further, to test the hypothesis that suppression of masculine copulatory behavior by ANG II involves interaction with the angiotensin AT-1 receptor, a highly selective nonpeptide antagonist (L-158,809) was administered in the drinking water (25 mg/liter) to a group of ANG II-infused animals. I.c.v. infusion of ANG II was associated with increases in systolic blood pressure and fluid intake. In copulatory tests after 3, 9 and 15 days of infusion, rats infused with ANG II exhibited increased latencies to the initiation of copulatory behavior and to ejaculation, as well as increased intervals to reinitiate copulatory behavior after the ejaculation. Administration of L-158,809 blocked the effects of i.c.v. infusion of ANG II on systolic blood pressure and fluid intake. Further, L-158,809 attenuated the effects of i.c.v. infusion of ANG II on parameters of copulatory behavior. Data from this study provide support for a modulatory role for ANG II in the regulation of sexual behavior. In addition, this regulation seems to involve the AT-1 receptor.