Positive chronotropic responses to cardiac alpha 1-adrenoreceptor activation in the pithed rat.
Adrenaline (0.1-10 micrograms/kg), noradrenaline (0.1-10 micrograms/kg) and phenylephrine (1-100 micrograms/kg) acted on both cardiac alpha 1- and beta-adrenoreceptors to induce positive chronotropic responses in the pithed rat. When beta-adrenoreceptors were blocked by propranolol (1 mg/kg), the residual chronotropic responses were due to activation of alpha 1-adrenoreceptors since they were significantly reduced by prazosin (10-100 micrograms/kg). Methoxamine (10-300 micrograms/kg) acted solely on cardiac alpha 1-adrenoreceptors to induce positive chronotropic responses which were abolished by prazosin (10-100 micrograms/kg) alone, as has been demonstrated previously for amidephrine. The rank order of potency for eliciting the positive chronotropic response to alpha 1-adrenoreceptor activation was adrenaline greater than noradrenaline greater than phenylephrine greater than methoxamine. The positive chronotropic responses to adrenaline (3-10 micrograms/kg), noradrenaline (3-10 micrograms/kg) and phenylephrine (30-100 micrograms/kg) produced by activating alpha 1-adrenoreceptors had a slower time course than did the chronotropic responses produced by activation of beta-adrenoreceptors.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D003655:Decerebrate State / Q000503:physiopathology; D004347:Drug Interactions; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D000316:Adrenergic alpha-Agonists; D010656:Phenylephrine; D008729:Methoxamine; D009638:Norepinephrine; D011224:Prazosin; D004837:Epinephrine