Adrenergic control of insulin release from isolated islet tissue in the rainbow trout, Salmo gairdneri R.

Immunoreactive insulin levels (IRI) were measured by a homologous fish insulin radioimmunoassay. An in vitro pancreatic islet superfusion technique was employed to monitor the changes in IRI in the presence and absence of specific adrenergic agonists and antagonists. Exogenous adrenaline at low concentrations (10(-10) M) inhibited IRI release but evoked an IRI stimulation at high concentrations (10(-6) M). The stimulation of IRI by adrenaline is thought to involve beta-adrenoceptors located postsynaptically on the beta-cell membrane as the effect of adrenaline was mimicked by the beta-agonist, isoproterenol, and abolished by the beta-antagonist, propranolol. Phentolamine (an alpha-antagonist) potentiated the adrenergic stimulation of IRI, whereas yohimbine (an alpha 2-antagonist) was without effect. Phenylephrine (alpha 1-adrenoceptor agonist) inhibited IRI release suggesting the presence of alpha 1-inhibitory adrenoceptors which exert a modulatory influence on adrenaline-stimulated insulin release.