Release of noradrenaline from the cat spleen by nerve stimulation and potassium.

Abstract

Release of noradrenaline from the perfused cat spleen, or from isolated spleen slices, in response to prolonged nerve stimulation or maintained depolarization by K was measured. Prolonged stimulation of the splenic nerves at 2, 10 and 30 Hz for 10 min evoked release, which was maximum during the first 2 min, and then declined during the remaining period of stimulation. When noradrenaline release was induced by high K from the perfused spleen or from isolated slices, it followed a similar time course to nerve stimulation. Similar results were obtained from phenoxybenzamine-treated spleens, using both modes of stimulation. Stimulation of the splenic nerves in Ca-free Krebs solution did not release noradrenaline. If Ca was introduced at a later stage during stimulation, the release was markedly diminished. In phenoxybenzamine- or phentolamine-treated spleens, stimulation of the nerves in the presence of Ca evoked a secretory response which was comparable to the one produced by introduction of Ca after a few minutes of nerve stimulation. Simultaneous application of Ca plus high K always produced a much greater secretion of noradrenaline than application of Ca after a few minutes of K depolarization. Release of noradrenaline by K from phenoxybenzamine-treated spleens was also much greater if Ca nad K were added simultaneously than addition of Ca after a few minutes of K depolarization. In the presence of maintained depolarization by K, tyramine was effective in causing release of noradrenaline.