Abstract
1. The effects of the α 1 adrenoceptor blockers indoramin, azapetine and phenoxybenzamine and the β adrenoceptor blockers propanolol and SK&F 92657 on the distribution and translocation of the pigment in the melanophores of the fiddler crab, Uca pugilator, were determined. 2. All of the α 1 blockers (but nonw of the β blockers) significantly inhibited the melanin dispersion which normally occurs when fiddler crabs are transferred from a white to a black background. 3. None of the drugs had a direct effect on the rate of pigment migration in the melanophores of isolated legs. 4. The results are consistent with the hypotheses that (a) norepinephrine produces melanin dispersion in Uca pugilator by triggering release of melanin-dispersing hormone (MDH) and (b) when fiddler crabs are transferred from a white to a black background α 1 adrenoceptor activation plays the dominant role in executing the MDH-release triggering action of norepineprhine.
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