ISSN:
1573-7241
Keywords:
xamoterol
;
noradrenaline
;
beta receptors
;
cardiac actions
;
vascular effects
;
coronary effect
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The hemodynamic and coronary effects of increasing doses of xamoterol, a beta-adrenoceptor partial agonist, were assessed in an anesthetized pig preparation in which cardiovascular reflexes were abolished and sympathetic tone was modified by infusion of noradrenaline (NA). Xamoterol, in basal conditions, increased heart rate (HR) from 104±12 to 120±13 beats/min (p〈.001); systolic, diastolic, and mean blood pressure, respectively, from 77±8 to 103±17 mmHg (p〈.01), from 48±7 to 70±12 mmHg (p〈.01), and from 58±7 to 84±14 mmHg (p〈.01); left ventricular dP/dT max from 2098±564 to 4205±937 mmHg/sec (p〈.001); and systemic vascular resistance (SVR) from 1745±564 to 2270±739 dynes sec cm−5 (p〈.01). The increase in HR and dP/dT max brought about by xamoterol was about 37% and 56%, resectively, of the maximum increase produced by NA. At the highest level of sympathetic tone, xamoterol reduced HR from 148±11 to 122±11 beats/min (p〈.001) and no significant change was observed in dP/dT max. The increase in blood pressure and SVR induced by xamoterol was maintained at each level of sympathetic tone. On the contrary, SVR did not change after NA, as expected, since receptors were fully blocked. For a given inotropic effect, xamoterol and NA produced a similar increase in coronary blood flow and myocardial O2 consumption. In conclusion, the results indicate that, in the areflexic pig, xamoterol acts as a partial beta1-agonist, with a more potent positive inotropic than chronotropic effect in basal conditions. At the highest level of sympathetic tone, it does antagonize the chronotropic, but not the inotropic, effect of NA. Xamoterol increases peripheral resistance and blood pressure possibly through a beta2 vascular blocking action, and the increase in contractility induced by xamoterol is paralleled by an increase in myocardial O2 consumption. No direct effects on coronary circulation are observed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01881533
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