Dual Adrenoceptor‐mediated Control of Noradrenaline Secretion from Human Vasoconstrictor Nerves: Facilitation by β‐receptors and Inhibition by α‐receptors

Sixth Gaddum Memorial Lecture National Institute for Medical Research, Mill Hill, January 1977

“…A similar effect was obtained with low concentrations of adrenaline (Stjarne & Brundin, 1975) although a further increase in the concentration of adrenaline led to inhibition of transnmitter release due to stimulation of a-presynaptic receptors. Stjarne & Brundin (1975) (Hedqvist & Moawad, 1975).…”

“…It is noteworthy that Stjarne & Brundin (1975) have shown that isoprenaline increases 13H1-noradrenaline release elicited by field stimulation from strips of human omental arteries and veins. A similar effect was obtained with low concentrations of adrenaline (Stjarne & Brundin, 1975) although a further increase in the concentration of adrenaline led to inhibition of transnmitter release due to stimulation of a-presynaptic receptors.…”

“…Propranolol reduced transmitter release elicited by nerve stimulation in guinea-pig isolated atria (AdlerGraschinsky & Langer, 1975) and in the calf muscle of the cat pretreated with phenoxybenzamine (Dahl6f et al, 1975). Yet, exposure to propranolol 0.1 I M did not reduce 3H-transmitter release from human omental arteries and veins (Stjarne & Brundin, 1975 Lewis (1974) reported that in the pithed rat preparation, chronic, but not acute administration of practolol reduced the pressor responses to preganglionic sympathetic stimulation.…”

“…Evidence for the presence of presynaptic jadrenoceptors in noradrenergic nerve endings It has recently been postulated that in addition to the presynaptic negative feed-back mechanism for noradrenaline released by nerve stimulation which is mediated via a-adrenoceptors, a positive feed-back mechanism exists in noradrenergic nerve endings that is triggered through the activation of presynaptic f,-adrenoceptors (Langer, Adler-Graschinsky & Adler-Graschinsky & Langer, 1975;Langer et al, 1975a;Stjarne & Brundin, 1975;Dahl6f, Ablad, Borg, Ek & Waldeck, 1975;Langer, 1976;Stjarme & Brundin, 1976a;Yamaguchi et al, 1977).…”

“…Note that isopr4naline induced a concentration-dependent increase in 3H-transmitter release, which was reversible by washing. Adler-Graschinsky & Langer, 1975;Langer et al, 1975b;Stjarne & Brundin, 1975;Hedqvist & Moawad, 1975;Stjdrne & Brundin, 1976a). The increase in transmitter release obtained in the presence of isoprenaline is independent of the a or nature of the response of the effector organ to the transmitter (Langer et al, 1975b).…”