Functional β1‐ and β2‐adrenoceptors in the human myocardium

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Abstract
Functional β‐adrenoceptor populations in the human heart were studiedin vitroin electrically‐paced strips of the right auricular and ventricular myocardium. The relative potency of selected agonists in producing inotropic responses (Tmax,T′max) in the presence of blockers for neuronal and extraneuronal uptakes was found to be as follows: isoprenaline > noradrenaline = adrenaline = salbutamol > dobutamine. Prenalterol had a negative inotropic effect in these preparations. The selective β1‐(practoloI) and β2‐(H 35/25) blockers reduced inotropic responses to adrenaline (Tmax,T′max) and noradrenaline (T′max) in the auricular strips. These results indicate the participation of β2‐adrenoceptors in inotropic responses in the human auricular and ventricular myocardium. For comparison, inotropic responses of electrically‐paced rat myocardium to β‐adrenergic agonists in the presence of blockers for neuronal and extraneuronal uptakes were likewise studied. The relative potencies forTmaxwere: noradrenaline = adrenaline > prenalterol > dobutamine = salbutamol. Given the high relative potency of salbutamol in the human myocardial strips (analogous to that previous shown in the β2‐dominated atria of the frog and trout) and the low relative potency of salbutamol in the rat tissue, these findings indicate a greater population of functionally active β2‐adrenoceptors in the human than in the rat myocardium.