Beta-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 beta-receptor stimulants and antagonists on 3H-noradrenaline release in response to stimulation by KC1 (75 mM). (--)-Isoprenaline 1X 10(-9)--1 X 10(-7) M) increased 20--25% the release of 3H-noradrenaline from cultured ganglia exposed to KC1. Isoprenaline did not modify either the spontaneous (non-calcium dependent) release of 3H-noradrenaline from cultured ganglia, or the KC1-stimulated release from fresh ganglia. The effect of (--)-isoprenaline was blocked by (--)-propranolol 5 X 10(-9) -- 1 X 10(-8) M and by butoxamine 10(-6) M, but not by (+)-propranolol (1 -- 5 X 10(-8) M), practolol (1 X 10(-8) -- 1 X 10(-6) M), or sotalol (1 X 10(-7) -- 1 X 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 beta-receptors in sympathetic nerve terminals may be involved in a positive feedback of noradrenaline release.