Comparison of intra-arterial and indirect blood pressures at rest and during isometric exercise in hypertensive patients before and after metoprolol

Interaction of clonidine and beta-blockers

On the hypothesis that non-selective beta-blockers can antagonize or reverse the antihypertensive effect of clonidine (C), 12 hypertensive outpatients were treated with C alone and in combination with propranolol (P), atenolol (A) and prazosin (Pz). C alone (0.11 or 0.22 mg b.i.d.) or in combination with P (80 mg b.i.d.) did not provide normotension. Changing P to A (50 mg b.i.d.) reduced supine systolic and diastolic pressures, which now were significantly lower (p less than 0.01) than during C alone. Changing A to P again resulted in elevated pressures. Pz (1 mg t.i.d.) added to the C+P regimen lowered supine blood pressures to the levels otherwise recorded during C+A. C dose-dependently contracted rabbit aortic spiral in vitro, reaching about 50% of maximum responses to noradrenaline. Pz abolished this response. P (0.1--10 micrograms/ml) but not A somewhat enhanced responses to high doses of C. Sotalol rather antagonized C contractions. We conclude that A but not P enhances the antihypertensive action of C. No hypertensive interaction was observed.

Exercise performance and beta-blockade

beta-Adrenoceptor blockers (beta-blockers) are common first-choice drugs in the treatment of various cardiovascular disorders. Physical exercise performed during single-dose administration of beta-blockers, however, is associated with an increased rate of perceived exertion; an effect which appears to be partly reduced with long term treatment. Although clinical doses of beta-blockade may reduce heart rate by 30 to 35%, during maximal exercise cardiac output is not equally reduced. Accordingly, most studies have demonstrated increased stroke volume after beta-blockade. This reduction in heart rate is typically accompanied by a decreased VO2max (5 to 15%) in both patients and healthy, trained subjects. This smaller reduction in VO2max, as compared with the decrease in cardiac output, is the result of a partly compensating increased arteriovenous O2 difference. Work capacity as reflected by the ability to perform intense short term or more prolonged steady-state exercise is also impaired following beta-blockade. beta-Adrenoceptors can be subdivided into types beta 1- and beta 2. Blockers which are specific for either beta 1-receptors (beta 1-selective blockers) or both beta 1- and beta 2 receptors (non-selective blockers) differ with regard to their effect on exercise performance. Exercise performance ability, irrespective of exercise intensity and duration, is impaired to a greater extent following non-selective than beta 1-selective blockade at equal reductions in heart rate. This response stems from a decreased energy flux through glycogenolysis during non-selective blockade treatment. Individuals receiving beta-blockade medication therefore show greater adaptive response to physical conditioning during treatment with beta 1-selective than non-selective blockade probably because of greater training intensity with the former therapy. Neither psychomotor performance nor muscular strength and power is negatively affected by beta-blockade. Nevertheless, the ability to perform athletic events requiring high levels of motor control under emotional stress but not high levels of aerobic or anaerobic energy release, is probably increased during beta-blockade.

Magnitude and mechanisms of the antihypertensive action of labetalol, including ambulatory assessment

The blood pressure (BP) effect and modes of action of a twice daily regimen of labetalol (mean 450 mg/day) were assessed in ten mild to moderate hypertensives using continuous ambulatory BP monitoring. The reflex control of BP during physiological interventions was examined just prior to the next dose of medication to estimate the residual alpha- and beta-adrenoceptor blockade. Global 24 h BP was reduced by 15/9 mm Hg, and home pressures by 13/11 mm Hg. The predominant antihypertensive effect was noted during the waking hours. During dynamic exercise significant inhibition of the heart rate and blood pressure rise occurred. Coupled with a reduction of the post-release BP 'overshoot' in Valsalva's manoeuvre, the response resembles that seen with beta-adrenoceptor blockade. A small alpha-adrenoceptor blocking action was evident in one patient's response to the Valsalva manoeuvre.

Effect of nitroglycerin ointment (Nitrong) on exercise tolerance and several circulatory parameters in patients with angina pectoris

Nine patients with coronary heart disease, 8 of whom were taking adrenergic beta-blockers, were tested by dynamic (bicycle) and isometric (sitting handgrip) exercise before and 2 and 6 h after application of nitroglycerin 30 mg in an ointment, or a matching placebo ointment, over 225 cm2 surface on the chest, in a double-blind, cross-over, single dose study. Exercise time until stopping from chest pain was significantly increased (by about 20%) by active ointment, and electrocardiographic ST-depression and chest pain intensity were significantly less pronounced during exercise both 2 and 6 h after application. During seated rest, active ointment also produced a significantly lower systolic blood pressure and a significantly higher heart rate at both 2 and 6 h, whereas during handgrip, significant differences from placebo were seen only at 2 h. All patients experienced headache for at least the 6 h of the study. At a given heart rate, ST-depression was less pronounced with active ointment than with placebo.

Anti-hypertensive action of labetalol: a detailed profile

Continuous, ambulatory blood pressure (BP) and self measured home recordings were used to study the response of ten mild to moderate hypertensives taking a twice daily labetalol dosage. Testing of cardiovascular reflexes was carried out 12 hours after a dose of drug. The mean 24 hour BP was reduced from 145/80 +/- 14/7 (SD) mmHg to 130/71 +/- 11/6 (p less than 0.001) and home BP from 147/96 +/- 15/9 to 134/84 +/- 10/9 (p less than 0.01). The predominant effect of labetalol was evident during the waking hours. A residual 9.5% BP reduction was seen 12 hours after a dose compared to an 11% lowering effect over the entire 24 hours (NS). No symptomatic hypotensive episodes were noted. Significant inhibition of heart rate and BP rise during dynamic exercise (p less than 0.01) and reduction of post-release BP "overshoot" (p less than 0.01) in Valsalva's manoeuvre indicated a beta adrenoceptor blocking effect. There was however a reduction in the rate of rise of BP during static handgrip (p less than 0.01) indicating a small alpha adrenoceptor blocking component. This study has demonstrated the efficacy of a twice daily regimen of labetalol in continuously lowering BP. The mode of action of the drug during exercise (static and dynamic) and Valsalva's manoeuvre would indicate a predominant beta adrenoceptor blocking action.

Circulatory effects of sublingual and oral sustained-release nitroglycerin in healthy young men

The effects on heart rate and blood pressure during standing, and on plethysmographic arterial pulsation in the calf, of nitroglycerin 0.5 mg sublingually, 6.5 mg orally and a placebo tablet were studied for up to 8 h. Sublingual nitroglycerin increased heart rate and arterial pulsation; the peak height and duration of these effects occurred at slightly different times. Oral nitroglycerin had no effect on heart rate but did increase pulsations as compared to placebo. In the orthostatic test, heart rate and pulse amplitude were affected by both forms of administration. Comparing the areas-under-curve for these variables for the two forms suggested that, in comparison with sublingual nitroglycerin, about 1/3 of the oral nitroglycerin was biologically effective over 8 h. Pulse plethysmography appeared to be the most sensitive method for "bioassay" of nitroglycerin.