[Interaction between load and beta-adrenergic stimulation in the modulation of diastolic function].
OBJECTIVE
Excessive afterload induces an upward shift of the diastolic pressure-volume relation. This diastolic dysfunction was attributed to the concomitant slowing of relaxation. The present study investigated to what extent beta-adrenergic stimulation could influence this effect.


METHODS
Beat-to-beat afterload elevations were induced in anaesthetised open-chest rabbits (n = 7) by narrowing the ascending aorta, to increase peak left ventricular pressure (LVPmax) from control up to isovolumetric. Afterload elevations were performed at baseline and during infusion of isoproterenol (0.15 mg/kg/min).


RESULTS
At baseline, LVPmax increased from 84 +/- 7 in the control beat to 154 +/- 10 mmHg in the isovolumetric beat, while during isoproterenol it increased from 88 +/- 4 to 184 +/- 11 mmHg (p < 0.01). After an isovolumetric beat, diastolic dysfunction was 7.9 +/- 1.5 mmHg at baseline and 2.6 +/- 0.5 mmHg during isoproterenol (p < 0.01). At all afterload levels, isoproterenol accelerated LVP fall (decreased the time constant tau), decreased the predicted time to completion of relaxation but did not influence the time available for the ventricle to relax.


CONCLUSIONS
Afterload induced diastolic dysfunction was attenuated by beta-adrenergic stimulation. These results, along with the inotropic and lusitropic effects of isoproterenol, may contribute to the acute improvement of cardiac function induced by beta-adrenergic stimulation. It may also help to explain the response to physical exercise and the pathophysiology of diastolic dysfunction in heart failure.
Leite-Moreira
A F
AF
Serviço de Fisiologia da Faculdade de Medicina da Universidade do Porto, Porto, Portugal. amoreira@med.up.pt
Correia-Pinto
J
J
Henriques-Coelho
T
T
D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D003971:Diastole / Q000187:drug effects* / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology*; D011817:Rabbits; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D016277:Ventricular Function, Left / Q000187:drug effects
D002316:Cardiotonic Agents; D011943:Receptors, Adrenergic, beta; D007545:Isoproterenol