Effect of nipradilol on silent myocardial ischemia, plasma beta-endorphin, and bradykinin in chronic stable angina

Day-to-day variability of the long-term fractal component of heart rate variability (β) and the effect of an antianginal agent in patients with silent myocardial ischemia

The deterioration of the long-term fractal component of heart rate variability (beta) is reported in patients with organic heart disease. To examine the day-to-day variability of beta and to study the effects of nipradilol (NIP), an antianginal agent, on beta in patients with coronary artery disease (CAD), we performed 24-hour ambulatory ECG (AECG) in 24 patients with silent myocardial ischemia (SMI) and obtained the conventional frequency domain heart rate variability (HRV) indices and beta using the MemCalc system. Patients were divided into two groups: group I consisted of 10 patients (64 +/- 5 years of age) for the assessment of the day-to-day variability of beta; group II comprised 14 patients (60 +/- 6 years of age) for evaluation of the effect of NIP (3 mg b.i.d). In group I, AECG was repeated twice a week, while AECG was recorded before NIP treatment (placebo) and on the last day of the 4-week NIP treatment in group II. In group I, there was significant correlation between the values of beta on day 1 and day 2 (r = 0.79, p < 0.05), the difference being 0.09 +/- 0.15 (coefficient of variance: 6.8%). Bland and Altman's analysis indicated that the results were easily reproducible, making this approach feasible for clinical use. In group II, NIP significantly decreased the values of beta by 10.6% (from -1.23 +/- 0.09 to -1.18 +/- 0.07; p < 0.05). NIP also significantly increased the conventional HRV indices. The degree of decrement of beta by NIP was larger than that of the day-to-day variability. In conclusion, a day-to-day variability exists in beta in patients with SMI, but its value is relatively small. A daily dose of 6 mg NIP ameliorates beta and overcomes this variability.

beta-Adrenoceptor blocking activities of nipradilol and its optical isomers in pig coronary artery

1. beta-Adrenoceptor blocking activities of nipradilol, its four optical isomers (RR, RS, SR, SS) and denitro nipradilol were evaluated using pig isolated coronary arteries. 2. (-)-Isoprenaline produced concentration-dependent relaxations of the arteries, which were antagonized by nipradilol, its four optical isomers or denitro nipradilol under KCl-induced contracture. 3. The order of pA2 values for beta-adrenoceptor blocking activities was SR > nipradilol > SS > or = denitro nipradilol > RR > RS. 4. The nitroxy group in nipradilol appears to enhance its beta-adrenoceptor blocking activity, because the beta-adrenoceptor blocking activity of nipradilol was more potent than that of denitro nipradilol. 5. Isomers that have the S configuration (SR, SS) at the 2' position (having a hydroxyl group) in the aryloxypropanolamine showed more potent beta-adrenoceptor blocking activity than isomers that have the R configuration (RR, RS). 6. Isomers that have the R configuration (SR, RR) at the 3 position (having a nitroxy group) in the benzopyran ring showed more potent beta-adrenoceptor blocking activity than those with the S configuration (SS, RS). 7. It is suggested that the difference in configuration of the chemical structure of nipradilol may result in variations of binding affinity for the beta-adrenoceptor.

Extent of ischemic stimulus and plasma beta-endorphin levels in silent myocardial ischemia

BACKGROUND

Beta-endorphin has been reported to play a role in the mechanism of silent myocardial ischemia.

OBJECTIVES

Plasma beta-endorphin levels during coronary angioplasty-induced silent and symptomatic myocardial ischemia were compared with those during exercise-induced silent ischemia.

METHODS AND RESULTS

The study population consisted of 40 nondiabetic patients with angioplasty-indicated coronary artery disease. All patients underwent exercise treadmill testing 2 to 4 days before angioplasty. Patients were divided into three groups: group 1, 10 patients with silent ischemia during exercise and angioplasty; group 2, 15 patients with silent ischemia during exercise and symptomatic ischemia during angioplasty; and group 3, 15 patients with symptomatic ischemia during both exercise and angioplasty. In group 1, plasma beta-endorphin levels during balloon inflation were significantly higher than in groups 2 and 3 and also significantly higher than during exercise. In group 2, plasma beta-endorphin levels were significantly elevated at exercise-induced silent myocardial ischemia and balloon-induced symptomatic myocardial ischemia, but the levels between exercise and balloon inflation were not significantly different.

CONCLUSIONS

For "silent" myocardial ischemia, it may be necessary for beta-endorphin levels to increase to sufficiently high levels to suppress anginal symptoms in response to the degree of ischemic stimuli.

Effect of carteolol on silent myocardial ischemia, variability in heart rate, and the pain-modulating system

To investigate the effects of carteolol, which is a nonselective beta-adrenergic agent with intrinsic sympathomimetic activity, on silent myocardial ischemia, exercise-induced myocardial ischemia, indexes of heart rate variability, and pain-modulating system, 20 patients (mean 60 +/- 9 years) with chronic stable angina underwent exercise treadmill testing and 24-hour ambulatory electrocardiographic monitoring during 2 weeks of carteolol administration (15 mg/day) in a double-blind, placebo-controlled design. Plasma levels of beta-endorphin and bradykinin and electrical pain stimulation to the skin were measured at rest and peak exercise. Indexes of heart rate variability of both time-domain and frequency-domain analysis were derived from 24-hour ambulatory electrocardiographic monitoring. Carteolol decreased maximal heart rate responses to daily activities during ambulatory monitoring and significantly reduced the median frequency and duration of silent myocardial ischemic episodes (from 1.0 to 0.0 events/24 hr and from 16 to 0 min/24 hr, respectively). Carteolol significantly decreased the rate-pressure product at rest and during exercise with improving maximal ST segment depression, suggesting amelioration of exercise-induced myocardial ischemia. Carteolol did not significantly affect plasma levels of beta-endorphin and bradykinin or pain threshold. It significantly decreased some indexes (standard deviation of all normal sinus R-R intervals in the entire 24-hour recording and standard deviation of the mean of all 5-minute segments of normal R-R intervals of a 24-hour recording) of heart rate variability. These results suggest that carteolol may reduce total myocardial ischemic burden by the reduction of cardiac oxygen demand during daily activities and exercise stress, while not affecting plasma levels of beta-endorphin, bradykinin, and pain threshold. Because carteolol tended to decrease indexes of heart rate variability, significant caution might be necessary in prescribing the beta-blocking agents with intrinsic sympathomimetic activity like carteolol to patients with potential serious arrhythmia.