title: Activation of prejunctional beta-adrenoceptors in rat atria by adrenaline applied exogenously or released as a co-transmitter.
abstract: 1 Adrenaline (10 nM) significantly enhanced the stimulation-induced efflux of radioactivity from rat atria previously incubated with [3H]-noradrenaline ([3H]-NA). This effect was abolished by metoprolol (.01 muM). 2 Adrenaline in a higher concentration (1 muM) and NA (1 muM) significantly reduced the stimulation-induced efflux of radioactivity. However, in the presence of phenoxybenzamine (10 muM), adrenaline (1 muM) enhanced the efflux, whereas NA (1 muM) had no effect. 3 In rat isolated atria pre-incubated with adrenaline and then incubated with NA, both catecholamines were taken up and were released by field stimulation. When pre-incubation was with adrenaline and incubation was with [3H]-NA, metoprolol decreased the stimulation-induced efflux of radioactivity. This effect did not occur if the atria were pre-incubated with NA instead of adrenaline, suggesting tht neuronally released adrenaline activates prejunctional beta-adrenoceptors. 4 In conscious rats, intravenously administered adrenaline (6.0 and 0.6 nmol/kg) was taken up and retained in the atria and could be released by field stimulation. The release was calcium-dependent from these rats up to 24 h after administration.
mesh_terms: D000818:Animals; D004837:Epinephrine / Q000378:metabolism / Q000494:pharmacology*; D006973:Hypertension / Q000378:metabolism; D066298:In Vitro Techniques; D008790:Metoprolol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*
chemical_list: D018377:Neurotransmitter Agents; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D008790:Metoprolol; D009638:Norepinephrine; D004837:Epinephrine