Effects of acute and chronic metoprolol administration during submaximal and maximal exercise

The effects of beta1-adrenergic blockade on cardiovascular oxygen flow in normoxic and hypoxic humans at exercise

At exercise steady state, the lower the arterial oxygen saturation (SaO(2)), the lower the O(2) return (QvO(2)). A linear relationship between these variables was demonstrated. Our conjecture is that this relationship describes a condition of predominant sympathetic activation, from which it is hypothesized that selective beta1-adrenergic blockade (BB) would reduce O(2) delivery (QaO(2)) and QvO(2). To test this hypothesis, we studied the effects of BB on QaO(2) and QvO(2) in exercising humans in normoxia and hypoxia. O(2) consumption VO(2), cardiac output Q, CO(2) rebreathing), heart rate, SaO(2) and haemoglobin concentration were measured on six subjects (age 25.5 +/- 2.4 years, mass 78.1 +/- 9.0 kg) in normoxia and hypoxia (inspired O(2) fraction of 0.11) at rest and steady-state exercises of 50, 100, and 150 W without (C) and with BB with metoprolol. Arterial O(2) concentration (CaO(2)), QaO(2) and QvO(2) were then computed. Heart rate, higher in hypoxia than in normoxia, decreased with BB. At each VO(2), Q was higher in hypoxia than in normoxia. With BB, it decreased during intense exercise in normoxia, at rest, and during light exercise in hypoxia. SaO(2) and CaO(2) were unaffected by BB. The QaO(2) changes under BB were parallel to those in Q.QvO(2) was unaffected by exercise in normoxia. In hypoxia the slope of the relationship between QaO(2) and VO(2) was lower than 1, indicating a reduction of QvO(2) with increasing workload. QvO(2) was a linear function of SaO(2) both in C and in BB. The line for BB was flatter than and below that for C. The resting QvO(2) in normoxia, lower than the corresponding exercise values, lied on the BB line. These results agree with the tested hypothesis. The two observed relationships between QvO(2) and SaO(2) apply to conditions of predominant sympathetic or vagal activation, respectively. Moving from one line to the other implies resetting of the cardiovascular regulation.

Do β-blockers prolong survival in heart failure only by inhibiting the β1-receptor? A perspective on the results of the COMET trial

Experimental and clinical studies indicate that carvedilol exerts multiple antiadrenergic effects in addition to beta(1)-receptor blockade, but the prognostic importance of these actions has long been debated. This controversy has now been substantially advanced by the results of the recently completed Carvedilol Or Metoprolol European Trial (COMET), which showed that carvedilol (25 mg twice daily) reduced mortality by 17% when compared with metoprolol (50 mg twice daily), P=.0017--a result that was consistent with the differences seen across earlier controlled trials with beta-blockers in survivors of an acute myocardial infarction and in patients with chronic heart failure. Questions have been raised about the interpretation of these findings in view of the fact that the trial did not use the dose or formulation of metoprolol that was shown to prolong life in a placebo-controlled trial (ie, Metoprolol CR/XL [Controlled Release] Randomized Intervention Trial in Heart Failure). Pharmacokinetic and pharmacodynamic analyses, however, indicate that the dosing regimen of metoprolol selected for use in the COMET trial produces a magnitude and time course of beta(1)-blockade during a 24-hour period that is similar to the dose of carvedilol targeted for use in the trial. These analyses suggest that the observed difference in the mortality effects of metoprolol and carvedilol is not related to a difference in the magnitude or time course of their beta(1)-blocking effects but instead reflect antiadrenergic effects of carvedilol in addition to beta(1)-blockade.

Exercise capacity, energy metabolism, and beta-adrenoceptor blockade. Comparison between a beta 1-selective and a non-selective beta blocker

The effects of beta 1 and beta 1/2 blockade on exercise capacity were studied in 9 healthy normotensive subjects. Progressive maximal bicycle ergometer tests, followed by an endurance test at 80% of maximal work load, were performed during randomized, double-blind 3 day treatment periods with placebo, atenolol (beta 1) and oxprenolol (beta 1/2). The reduction of maximal work capacity (ca. 10%) was similar with atenolol and oxprenolol, despite a more pronounced maximal heart rate reduction with atenolol (from 175 +/- 2 to 132 +/- 3 beats.min-1) than with oxprenolol (to 138 +/- 2 beats.min-1). Exercise time during the endurance test was reduced from 36 +/- 4 min with placebo to 27 +/- 3 min with atenolol (p less than 0.05) and 24 +/- 3 min with oxprenolol (p less than 0.01) (atenolol vs. oxprenolol: p less than 0.05). During the endurance test, plasma glycerol and non-esterified fatty acid concentrations were reduced with both atenolol and oxprenolol. The glycerol reduction was more pronounced with oxprenolol than with atenolol, plasma NEFA concentrations being similar. Plasma glucose and lactate concentrations were reduced by oxprenolol but not with atenolol. These data show that submaximal exercise capacity at work loads representing similar relative exercise intensities is reduced during non-selective and beta 1-selective beta blockade. This reduction may be related to the effects of beta 1 blockade on energy metabolism, with possibly an additional effect of beta 2 blockade.

The effect of verapamil on cardiovascular and metabolic responses to exercise

In a double-blind cross-over study, the effects of verapamil on the cardiovascular and metabolic changes during a progressive maximal exercise test were studied in 12 healthy volunteers. Each subject was treated with placebo and verapamil in 3 different dosages: 3 X 40, 3 X 80 and 3 X 120 mg X d-1 in random order. Drugs were administered for 2 days; on the 3rd day, 2 h after the last dose, a progressive exercise test until exhaustion was performed on a bicycle ergometer. No significant differences in maximal exercise capacity were found between the 4 groups of medication. VO2, VCO2, and VE were also unaffected by verapamil administration. Heart rate during exercise was reduced dose-dependently (p less than 0.001). With the highest dose of verapamil, maximal heart rate was reduced by 13 +/- 1 beats X min-1. No effect could be shown on parameters of carbohydrate and fat metabolism. Perceived exertion, estimated by the Borg scale, did not differ between placebo and the 3 medication groups. The study shows that despite a distinct reduction of heart rate, maximal exercise capacity remains unaffected after verapamil use.