Adrenoceptors and adenyl cyclase in gills.

The content of cyclic 3',5'-adenosine monophosphate (cAMP) in the gills of the mullet (Mugil capito) has been measured. The basal level was found to be 2.9+/-0.3 pmol/mg wet weight. When fish were first anaesthetized with MS222 (tricaine) and the gills perfused to remove blood, the concentration of cAMP was raised to 14.3+/-1.9 pmol/mg wet weight.Adrenaline caused a significant increase in cAMP content, an effect that was blocked by propranalol, a beta-adrenoceptor antagonist. In the presence of the alpha-adrenoceptor block- ing agent phentolamine, adrenaline still caused an increase in nucleotide content.The results are discussed in relation to adrenaline and the adenyl cyclase system.