Adrenergic mechanisms associated with the movement of platelets in iridophores from the freshwater goby, Odontobutis obscura.

1. Cultured iridophores from the freshwater goby, Odontobutis obscura, were used to investigate adrenergic mechanisms of movement of platelets in the iridophores. 2. Norepinephrine, which was assumed to be the transmitter of the iridophore nerves, induced dispersion of platelets within the cells. 3. The effect of norepinephrine was inhibited by an alpha-adrenergic antagonist, yohimbine, but not by a beta-adrenergic antagonist, propranolol. 4. Isoproterenol, a beta-adrenergic agonist, failed to bring about aggregation of platelets. 5. Forskolin, an activator of adenylate cyclase, was effective in inducing aggregation of platelets. 6. 8-Br-cAMP caused the aggregation of platelets and inhibited the norepinephrine-induced dispersion of platelets. 7. It appears that the adrenoceptors of the iridophores of this species are solely of the alpha type; they mediate the dispersion of platelets; and an increase in intracellular levels of cAMP induces the aggregation of platelets.