β-Adrenoceptors modulate noradrenaline release from axonal sprouts in cultured rat superior cervical ganglia

Superior cervical ganglia of rats grown in organ culture were used to study the effect of β-receptor stimulants and antagonists on ³H-noradrenaline release in response to stimulation by KCl (75 mM). (-)-Isoprenaline 1 × 10^-9 -1×10^-7 M) increased by 20-25% the release of ³H-noradrenaline from cultured ganglia exposed to KCl. Isoprenaline did not modify either the spontaneous (non-calcium dependent) release of ³H-noradrenaline from cultured ganglia, or the KCl-stimulated release from fresh ganglia. The effect of (-)-isoprenaline was blocked by (-)-propranolol 5 × 10^-9 - 1 sx 10 ^-8 M and by butoxamine 10^-6 M, but not by (+)-propranolol (1-5 × 10^-8 M), practolol (1 × 10^-8 - 1 × 10^-6 M), or sotalol (1 × 10^-7 - 1 × 10^-6 M). Isoprenaline induced augmentation of ³H-noradrenaline release and its antagonism by (-)-propranolol still occurred in the presence of DMI. It is suggested that presynaptic β-receptors in sympathetic nerve terminals may be involved in a positive feedback of noradrenaline release.