Alpha-adrenergic stimulation contributes to the inotropic effect of noradrenaline.
The alpha- and beta-adrenoceptor mediated inotropic effects of noradrenaline were determined in rat heart papillary muscle. The pure alpha-adrenergic inotropic effect, obtained in the presence of the beta-blocker timolol, was about half the pure beta-adrenergic inotropic effect, obtained in the presence of the alpha-blocker prazosin. The maximal inotropic effect of noradrenaline in the absence of blockers was, however, of the same magnitude as the pure beta-adrenergic effect. The alpha- and beta-adrenergic components of the inotropic response to noradrenaline were determined as those reversed by prazosin and timolol, respectively. They were smaller than the pure effects evoked separately. When beta-stimulation by noradrenaline was attenuated by carbachol, the alpha-adrenergic inotropic component was increased. Thus the alpha-effect is increased when the beta-adrenergic effect is antagonized. The alpha-adrenergic inotropic component of noradrenaline seems to play a variable role depending upon the degree of concomitant beta-receptor stimulation in the heart.
Osnes
J B
JB
Department of Pharmacology, Univ. of Oslo, Norway.
Christiansen
H B
HB
Horgmo
G I
GI
Schiander
I G
IG
Skomedal
T
T
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology; D013999:Timolol / Q000494:pharmacology
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D013999:Timolol; D002217:Carbachol; D009638:Norepinephrine; D011224:Prazosin