Elasmobranch color change: A short review and novel data on hormone regulation

Skins of Potamotrygon reticulatus are light in color in vitro, exhibiting p unctate melanophores. cl-Melanocyte stimulating hormone (EC50 = 4.58 x 10(- 9) M) and prolactin (EC50 = 1.44 x 10(-9) M) darken the skins in a dose-dep endent manner. The endothelins ET-1, ET-2 and ET-3, and the purines, ATP, a nd uracil triphosphate (UTP) were not able to induce either skin lightening or darkening. Forskolin and the calcium ionophore A23187 promoted a dose-d ependent darkening response, whereas N-2 2'-O-dibutyryl guanosine 3'-5'-cyc lic monophosphate (db cyclic GMP), phorbol-12-myristate-13-acetate (TPA), a nd 1-oleoyl-2-acetyl-sn-glycerol (OAG) were ineffective. The maximal respon se obtained with the calcium ionophore A23187 was only 76% of maximal darke ning. These results indicate that the cyclic adenosine 3'-5'-monophosphate (cAMP) pathway is probably involved in the pigment dispersion of P. reticul atus melanophores. Other experiments should be done to further investigate how cytosolic calcium may be physiologically increased, and the existence o f a putative cross-talk between calcium and cAMP signals. In conclusion, th e only hormones effective on P. reticulatus melanophores were prolactin and a-MSH. No aggregating agent has been shown to antagonize these actions. Pr olactin effect on elasmobranch melanophores adds a novel physiological role to this ancient hormone. (C) 1999 Wiley-Liss, Inc.