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

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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.