Dissociation between duration of plasma catecholamine and blood pressure responses to beta-adrenergic blockade in normotensive subjects during physical exercise

Plasma concentrations of free and sulfoconjugated dopamine, epinephrine, and norepinephrine in healthy infants and children

Plasma concentrations of free and sulfoconjugated catecholamines were measured in healthy infants and children under resting conditions. Free norepinephrine and epinephrine levels were up to three times higher in healthy children under 2 years than in adults, even under true resting conditions. In contrast, free dopamine concentrations of all age groups fell within the normal range for adults. The levels of sulfoconjugation were in the adult range.

Studies on the uptake and release of propranolol and the effects of propranolol on catecholamines in cultures of bovine adrenal chromaffin cells

Uptake and release of [3H]l-propranolol and the effects of propranolol on the uptake and release of [3H]norepinephrine were studied in cultures of isolated bovine adrenal chromaffin cells. [3H]l-Propranolol uptake increased with increasing [3H]l-propranolol concentration from 10(-7) M to 10(-3) M and was not saturable in this concentration range. [3H]l-Propranolol uptake was equally inhibited by l- and d-propranolol, indicating that the uptake is not stereoselective. [3H]l-Propranolol uptake differed from [3H]norepinephrine uptake in two respects: [3H]l-propranolol uptake was 44-50 times greater than [3H]norepinephrine uptake at early non-equilibrium time periods, and [3H]l-propranolol uptake was not Na+ dependent and was not inhibited by desipramine, indicating that [3H]l-propranolol is not taken up by the biogenic amine transport system. In cells preloaded with [3H]l-propranolol, two agents, veratridine and tyramine, stimulated an increased release of [3H]l-propranolol into the medium. However, veratridine-induced [3H]l-propranolol release was inhibited only slightly by the Na+ channel blocker tetrodotoxin, and tyramine-induced [3H]l-propranolol release was not inhibited by desipramine. In addition, K+, carbachol and the physiological mediator of adrenal catecholamine release, acetylcholine, failed to evoke [3H]l-propranolol release. Therefore, it is unlikely that propranolol is released in response to physiological stimulation of adrenal chromaffin cells in animals administered propranolol in vivo. l-Propranolol inhibited [3H]norepinephrine uptake by chromaffin cells with an IC50 for l-propranolol of 5 X 10(-6) M; d-propranolol was equally potent for this effect at lower propranolol concentrations. By themselves, neither l- nor d-propranolol had any effect on [3H]norepinephrine release from the cells. However, l-propranolol inhibited carbachol-induced [3H]norepinephrine release with an IC50 for l-propranolol of 5 X 10(-7) M to 10(-6) M. At these lower concentrations, d-propranolol had no effect on carbachol-induced [3H]norepinephrine release, indicating that the inhibition by l-propranolol may be mediated via beta-adrenoceptors on chromaffin cells.

Unchanged peripheral sympathetic activity following withdrawal of chronic metoprolol treatment. A study of noradrenaline concentrations and kinetics in plasma

Noradrenaline plasma kinetics were assessed in 17 male patients, who had been treated with metoprolol 100-200 mg daily (n = 8) or placebo for 3 years after an acute myocardial infarction, before and 1 week after gradual withdrawal (during 1 week) of the study treatment. Endogenous noradrenaline concentrations in plasma were measured by high performance liquid chromatography. Noradrenaline spillover rate, plasma clearance and the t1/2 for the rapid removal from plasma were determined by radio-tracer methodology. During treatment the plasma noradrenaline concentrations and noradrenaline plasma kinetic variables were similar in the two groups. Venous plasma noradrenaline concentrations were more closely correlated to the spillover rates of noradrenaline to plasma than to the clearance of noradrenaline from plasma, but the spillover rates were correlated to the clearance rates. Following the withdrawal of metoprolol noradrenaline clearance from plasma increased slightly (by 18 +/- 5%, P less than 0.05), but the plasma concentrations and spillover rates of noradrenaline were unchanged. In the placebo group withdrawal did not result in any significant changes. Our results indicate that a generalised increase in sympathetic nerve activity is not the cause of so-called rebound phenomena following withdrawal of chronic beta-adrenoceptor blockade.

Rebound phenomena following gradual withdrawal of chronic metoprolol treatment in patients with ischemic heart disease

Metoprolol or placebo was gradually withdrawn during 1 week in 115 patients participating in a 3-year, double-blind, postinfarction study. During the first month after withdrawal mental symptoms and increased cardiac symptoms occurred significantly more frequently in the metoprolol group. Disabling symptoms requiring reinstitution of treatment were seen in 14 of 58 in the metoprolol group vs 4 of 57 in the placebo group (p less than 0.05). In the metoprolol group, there was a rebound increase of basal heart rate and of the heart rate response to orthostatic testing during 3 weeks after withdrawal, when compared to values obtained 6 months later. In 27 patients plasma catecholamine levels were analyzed during repeated exercise tests and orthostatic provocations. Plasma norepinephrine and epinephrine responses to exercise were reduced 1 week after completion of withdrawal. At this time norepinephrine levels tended to be lower in relation to heart rate at all work loads. Our laboratory findings may be related to increased beta-adrenoceptor responsiveness, but unmasking of ischemic symptoms probably contributed to the clinical findings.

Inhibition of synaptosomal [3H]noradrenaline uptake by beta-adrenoceptor blocking drugs: influence of lipophilicity

Ten beta-adrenoceptor blocking drugs varying in lipophilicity and beta-adrenoceptor blocking potency were examined for inhibitory effects on synaptosomal [3H]noradrenaline uptake. All compounds produced a concentration-dependent inhibition of noradrenaline uptake, but were at least one order of magnitude less potent than desmethylimipramine and cocaine. The order of potency was pronethalol greater than propranolol greater than betaxolol greater than alprenolol greater than oxprenolol greater than practolol greater than metoprolol greater than acebutolol greater than sotalol greater than atenolol, with IC50 values ranging from 4.0 X 10(-6) to 2.2 X 10(-3) M. Uptake inhibition was unrelated to beta-adrenoceptor blocking potency, but was highly correlated with drug lipophilicity. (+)-Propranolol was an effective uptake inhibitor, as was the local anaesthetic procaine. Kinetic analysis of uptake inhibition by propranolol, oxprenolol, metoprolol and procaine revealed a mixed inhibition for all four agents examined. It is suggested that this effect of beta-adrenoceptor blockers may be mediated, at least in part, by an action on membrane phospholipids associated with the noradrenaline carrier protein, and that noradrenaline uptake inhibition may underlie certain central side-effects observed with some drugs in this group.

Exercise-induced increments in plasma levels of propranolol and noradrenaline

Exercise-induced changes in the plasma levels of propranolol and noradrenaline were determined in nine volunteers. Total plasma propranolol levels were increased during submaximal treadmill exercise, with exercise-induced increments of 13 +/- 4% at 4 h after the last dose, 18 +/- 7% at 9 h and 41 +/- 5% at 16 h. Exercise-induced increments in plasma propranolol were observed after single as well as repeated doses. During exercise, increments in plasma propranolol were correlated temporally with changes in plasma noradrenaline. Exercise-induced increments in plasma noradrenaline were greater during propranolol administration than during placebo periods. The changes in plasma propranolol concentration during exercise may reflect a redistribution of propranolol at its site(s) of action.

Plasma catecholamines in children

Plasma catecholamine concentrations in 46 children of various ages were determined by a sensitive radioenzymatic assay. Noradrenaline levels were found to be in the same range as in adults, whereas adrenaline levels in a few of the children were abnormally high.

The effect of captopril and propranolol on the responses to posture and isometric exercise in patients with essential hypertension

The effects of captopril and propranolol on blood pressure, heart rate and plasma noradrenaline, renin and aldosterone, and on the responses to changes in posture and to isometric exercise were measured in patients with essential hypertension. During placebo administration blood pressure, heart rate and plasma noradrenaline rose on standing and during isometric exercise. The rise in diastolic blood pressure during isometric exercise correlated significantly with the rise in plasma noradrenaline. During captopril treatment blood pressure was significantly lower than during placebo administration when the patients were lying, standing or sitting, but the reduction during isometric exercise was not significant. Plasma renin increased, but heart rate, plasma noradrenaline and plasma aldosterone remained unchanged. The acute changes in blood pressure, heart rate and plasma noradrenaline produced by standing and isometric exercise during captopril treatment were similar to those during placebo administration. During propranolol treatment diastolic blood pressure was significantly lower than during placebo administration when the patients were lying, standing or sitting and during isometric exercise. Heart rate also fell. Plasma noradrenaline during standing, sitting and isometric exercise was significantly greater than during placebo administration. The changes in plasma noradrenaline measured during propranolol treatment with the patients supine were negatively correlated with noradrenaline values obtained during placebo administration: plasma noradrenaline fell in patients with higher, and increased in those with lower, initial concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Atenolol reduces blood pressure and FEV in normal subjects

In a double-blind placebo controlled cross-over trial involving six subjects, atenolol, taken by mouth for 3 days, caused a statistically significant reduction in blood pressure and FEV₁.