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 (0.1 LM).2 Adrenaline in a higher concentration (1 pM) and NA (1 ylM) significantly reduced the stimulation-induced efflux of radioactivity. However, in the presence of phenoxybenzamine (10 gM), adrenaline (1 pM) enhanced the efflux, whereas NA (1 JM) 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 that neuronally released adrenaline activates prejunctional fi-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.

No abstract

1. Adrenaline can enhance the stimulation-induced release of transmitter noradrenaline in sympathetically innervated tissues by activating prejunctional beta-adrenoceptors. 2. Adrenaline incorporated into sympathetic transmitter stores by neuronal uptake can be subsequently released as a co-transmitter and can then activate prejunctional beta-adrenoceptors, thus completing a facilitatory feedback loop. 3. Rats chronically treated with adrenaline develop elevated blood pressures compared to control rats. beta-Adrenoceptor blockade prevents the rise in blood pressure. 4. Activation by adrenaline of facilitatory prejunctional beta-adrenoceptors of sympathetic nerves innervating cardiovascular effector tissues may explain adrenaline-induced rises in blood pressure.

No abstract

No abstract