<img src='/image/spc_char/alpha.gif'>₁ and <img src='/image/spc_char/alpha.gif'>₂ adrenoceptor mediated melanosome aggregatory responses <i style="">in vitro</i> in <i style="">Oreochromis mossambica </i>(Peters) melanophores

Abstract

Effects of specific and non-specific adrenoceptor agonists and antagonists were examined on the isolated scale melanophores of <i style="">O. mossambica</i> in physiological Ringer solution. The responses were recorded as melanophore size index. It was observed that adrenaline, nor-adrenaline, phenylpropanolamine, clonidine and phenylepherine induced melanosome aggregation in a dose-dependent manner. Denervation of the fish melanophores increased the sensitivity of the melanophores to adrenaline but not to nor-adrenaline. Phentolamine (3.55<img src='/image/spc_char/cross.gif'>10^-5 <i style="">M</i>), prazosin (2.38<img src='/image/spc_char/cross.gif'>10^-5 <i style="">M</i>) and yohimbine (2.821<img src='/image/spc_char/cross.gif'>10^-5 <i style="">M</i>) significantly inhibited the aggregatory responses of the fish melanophores to adrenaline, nor-adrenaline, clonidine and phenylepherine. The blocking effect of yohimbine was significantly higher than that of prazosin. It is concluded that the effect of adrenaline is directly mediated through the receptors and <img src='/image/spc_char/alpha.gif'>₂ adrenoceptors are predominantly involved in the aggregatory responses of this fish melanophores, while <img src='/image/spc_char/alpha.gif'>₁ adrenoceptors presence has been indicated.