Release of adrenergic transmitter from terminal nerve plexus in artery

Studies of the release of the adrenergic transmitter in the rabbit pulmonary artery have been carried out in vitro. At a stimulation frequency of 10 per second, the release was 52.9 pg per gram wet weight per pulse. The mean number of nodes or varicosities per gram wet weight of artery was 9.3×10⁷. If 80% of the released transmitter is taken up by tissues in the artery wall, these values correspond to the average release of approximately 400 molecules ofl-norepinephrine per node per pulse. The transmitter concentrations in the region of the muscle in the outermost lamina of the vessel during sympathetic activity are discussed in relation to the spatial dimensions of the neuroeffector cleft. The release of the total contents of a vesicle on the average every 7 or 8 pulses from each node is consistent with these requirements.