AJP - Heart and Circulatory Physiology, Vol 235, Issue 6 803-H808, Copyright © 1978 by American Physiological Society
Release of norepinephrine by sympathetic nerve stimulation from rabbit lungs
E. Y. Tong, A. A. Mathe and P. W. Tisher
Rabbit lungs were perfused via the pulmonary artery and norepinephrine (NE)
measured in the outflows. The basal NE level was approximately 3 ng/min.
Electrical stimulation (50 V, 1 ms, 10 Hz) of the sympathetic nerves
doubled the NE release. Hexamethonium (10(-4) and 10(-5) M) had no effect
on the release of NE. Administration of a monoamine oxidase (MAO)
inhibitor, pargyline (70 mg/kg) resulted in a 20-fold NE increase by nerve
stimulation, implying that the bulk of the amine does not reach the
systemic circulation due to an active MAO. Methacholine (1 and 10
micrograms/ml) inhibited NE release by nerve stimulation. This inhibition
was abolished by atropine (5 micrograms/ml). It is suggested that a
muscarinic inhibitory mechanism may regulate the NE release in the lung.
PGE2 (100 ng/ml), but not PGS2alpha, (100 ng/ml), depressed NE release
during nerve stimulation, whereas indomethacin (10 mg/kg) enhanced NE
release before, during, and after nerve stimulation in seemingly normal
animals. This indicates the existence of another presynaptic inhibitory
mechanism for NE release in the lung: a PGE-mediated inhibition.
