ISSN:
1432-1041
Keywords:
pindolol
;
propranolol
;
beta-adrenergic activity
;
beta-adrenergic sensitivity
;
beta-blocking agents
;
intrinsic sympathomimetic action
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Medicine
Notes:
Summary To investigate the mechanism of the relative beta-antagonist and agonist properties of pindolol, the cardiovascular effects of i.v. pindolol 0.01 mg/kg were studied in 23 subjects with different baseline levels of cardiac beta-adrenergic function. Baseline cardiac beta-adrenergic activity was assessed by the decrease in heart rate following intravenous propranolol 0.2 mg/kg (ΔHRβ) after parasympathetic blockade with intravenous atropine 0.04 mg/kg. Cardiac beta-adrenergic sensitivity was defined by the positive chronotropic effect of a three minute infusion of isoprenaline 0.005 µg/kg/min. The chronotropic effect of intravenous pindolol was negatively correlated with resting beta-adrenergic activity (R=−0.81, p〈0.001). The traditional point of ΔHRβ, at which pindolol shifted from beta-antagonist to beta-agonist action, was 17 beats/min, i.e. pindolol decreased heart rate in subjects with ΔHRβ greater than 17 bpm, and increased heart rate in those with ΔHRβ less than 17 bpm. The chronotropic effect of intravenous pindolol, however, was positively correlated with beta-sensitivity (R=+0.73, p〈0.001). Thus subjects with the greatest increment in heart rate with isoprenaline had an increased heart rate with pindolol, while those with the lowest increment in heart rate with isoprenaline had a decreased heart rate with pindolol. Intravenous pindolol decreased cardiac index and increased total peripheral resistance in the group with ΔHRβ more than 17 bpm, and it had the contrary actions in the group with ΔHRβ less than 17 bpm. Blood pressure in both groups was not significantly changed by pindolol. Compared to endogenous catecholamines, pindolol was considered to possess higher beta-adrenocepter affinity and weaker beta-adrenoceptor stimulating action. Therefore, pindolol produced a net beta-blocking action in subjects with elevated cardiovascular sympathetic nervous activity and beta-stimulating action in subjects with reduced sympathetic nervous activity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00542539
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