Serotonin and N-acetylserotonin effects on pigment cells of the toad Bufo ictericus: pharmacological characterization of melatonin receptors.
Melatonin is a skin lightening agonist of the toad Bufo ictericus. The hormone also exhibits an autodesensitizing action as well as an inhibitory activity on the darkening response to alpha-MSH. In an attempt to pharmacologically characterize the melatonin receptor of the toad pigment cells, serotonin and N-acetylserotonin (intermediate products of melatonin biosynthesis) biological activities were compared to melatonin effects. Serotonin (6.4 x 10(-5) to 10(-9) M) exhibited no lightening or inhibitory activity on MSH-elicited darkening responses or melatonin-elicited lightening responses. N-acetylserotonin, although less potent than melatonin, elicited a significant lightening response on previously MSH-darkened skins. Previous exposure of the skins with N-acetylserotonin reduced both MSH-induced darkening and melatonin-induced lightening in MSH-darkened skins. These results suggest a competitive inhibition of melatonin by N-acetylserotonin and indicate that melatonin receptors in B. ictericus pigment cells may be similar to ML-1 type found in chicken retina.
Filadelfi
A M
AM
Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, Brazil.
Castrucci
A M
AM
D000818:Animals; D002025:Bufonidae; D002856:Chromatophores / Q000187:drug effects*; D008297:Male; D008550:Melatonin / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000187:drug effects*; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects*; D044094:Receptors, Melatonin; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D012880:Skin Pigmentation / Q000187:drug effects; D000521:alpha-MSH / Q000494:pharmacology
D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D012701:Serotonin; D000521:alpha-MSH; D008550:Melatonin; C006389:N-acetylserotonin