Abstract
The contribution of α-AR stimulation (S) to the total inotropic effect (IE) of NA during full β-ARS has been questioned. The present study reveals a way of demonstrating an α-AR effect in the presence of full β-ARS by studying the reversal responses to AB at supramaximal NA stimulation in rat papillary muscles. The response was rapidly reversed (t50 = 2.8 ± 0.2 min) by simultaneous addition of the β-blocker timolol and the α-blocker prazosin. When AB were added sequentially (5-10 minutes apart), two IC in the inotropic response to NA could be demonstrated: one IC which was sensitive to timolol (73.3 ± 6.9 % of total response) and was taken as β-AR mediated and one IC which was sensitive to prazosin (26.7 ± 5.7 % of total response) and was taken as α-AR mediated. Thus, there is a significant contribution also from an α-AR effect. There is a mutual inhibition of one component upon the other as the expression of both α-AR and β-AR effects was less during combined AR stimulation than when the receptor populations were stimulated separately.
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Osnes, JB., Schiander, I. & Skomedal, T. 106: BOTH α- AND β-ADRENORECEPTOR (AR) MEDIATED INOTROPIC COMPONENTS (IC) OF NORADRENALINE (NA) ARE REVEALED BY REVERSING THE RESPONSE IN MYOCARDIUM BY ADRENERGIC BLOCKERS (AB). Pediatr Res 24, 277 (1988). https://doi.org/10.1203/00006450-198808000-00131
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DOI: https://doi.org/10.1203/00006450-198808000-00131