Section 6
Chapter 5,250

Effect of isoprenaline on noradrenaline release from sympathetic neurones in rabbit isolated pulmonary artery

Nedergaard, O.A.

Naunyn-Schmiedeberg's Archives of Pharmacology 336(2): 176-182


ISSN/ISBN: 0028-1298
PMID: 2825040
DOI: 10.1007/bf00165802
Accession: 005249254

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The aim of the present work was to demonstrate the presence of presynaptic .beta.-adrenoceptors in the rabbit isolated pulmonary artery by investigating the effect of isoprenaline on 3H-noradrenaline (3H-NA) release evoked by electrical field stimulation. (-)-Isoprenaline (10-7-10-6 mol/l) had no effect on the 3H-overflow evoked by stimulation (3 Hz) of the pulmonary artery preloaded with 3H-NA. At 10-5 mol/l, (-)-isoprenaline reduced the 3H-overflow by maximally 39%. (-)-Isoprenaline (10-5 mol/l) caused an inhibition that remained almost constant with time. The same results were obtained with (-)-isoprenaline (10-7-3 .times. 10-5 mol/l) in the presence of cocaine (3 .times. 10-5 mol/l), corticosterone (4 .times. 10-5 mol/l), and the catechol-O-methyltransferase inhibitor U-0521 (3',4'-dihydroxy-2-methylpropiophenone) (10-4 mol/l). In the presence of cocaine plus corticosterone, (-)-isoprenaline (3 .times. 10-10-10-7 mol/l) had no effect on the 3H-overflow evoked by stimulation at 1 Hz. At 10-6 mol/l (-)-isoprenaline slightly reduced the 3H-overflow. At 10 Hz, (-)-isoprenaline (10-6-3 .times. 10-5 mol/l) decreased the 3H-overflow and had no effect at 10-7 mol/l. In the presence of either rauwolscine (10-6 mol/l), phentolamine (10-6 mol/l) or the phosphodiesterase inhibitor ICI 63,197 (3 .times. 10-5 mol/l), (-)-isoprenaline (10-7-10-6 mol/l) did not enhance the stimulation-evoked 3H-overflow. (.+-.)-Propranolol (10-7-10-5 mol/l) did not alter the stimulation-evoked 3H-overflow. At 3 .times. 10-5 mol/l, this antagonist reduced the neurogenic response by 50%. (.+-.)-Propranolol (10-6 mol/l) did not alter the effect of (-)-isoprenaline (10-7-3 .times. 10-5 mol/l) on the stimulation-evoked 3H-overflow. (+)-Isoprenaline (10-7-3 .times. 10-5 mol/l) enhanced slightly the stimulation-evoked 3H-overflow. No enhancement was seen in the presence of either (.+-.)-propranolol (10-6 mol/l) or rauwolscine (10-6 mol/l). The results suggest that postganglionic sympathetic nerve terminals in rabbit pulmonary artery do not possess facilitatory .beta.-adrenoceptors.

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