Abstract
1. 1. In vitro skin pieces of the plaice dispersed their melanophore pigment in Na +-rich solution. Pigment aggregation was induced by catecholamines in the potency order dopamine > noradrenaline > adrenaline > isoprenaline. Tyramine was the most active amine tested but its actions were abolished by reserpine. 2. 2. Melanophore pigment aggregation in the presence of K + and Ca 2+ was prevented by alpha-adrenergic blockade (yohimbine > piperoxane > dibenamine > phentolamine) or by adrenergic neurone blockade (reserpine > bretylium > guanethidine). Beta-blockade with propranolol was ineffective. 3. 3. Cholinergic drugs induced slow and delayed pigment dispersion (pilocarpine > carbachol > arecoline > acetylcholine) whereas atropine and histamine were more potent and acted faster. 4. 4. Our results support the role of alpha-adrenergic receptors in melanophore pigment aggregation and indicate a possible role of histamine in dispersion.
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