Effects of dissociation and culture on the maintenance of insulin, glucagon and somatostatin release by neonatal rat islets of Langerhans

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.

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate enhances the long-term maintenance of pancreatic islet B cell differentiated function in tissue culture

A study was undertaken to examine the effects of the tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, on pancreatic islet B cell differentiated function and number. Islets from 3-day-old rats were maintained in tissue culture for up to 30 days with or without the addition of the phorbol ester. Changes in the insulin content of the media and tissue were determined at 48 hr and weekly intervals, respectively, using radioimmunoassay. The 30-day cumulative output of insulin into the medium was increased almost 2-fold and the tissue insulin content was increased 4-fold by the phorbol ester. Counts of cell smears processed for the immunocytochemical localization of insulin indicated no effect on the total numbers of B cells or non-B cells in either control or treated cultures. This enhanced maintenance of islet B cell differentiated function by 12-O-tetradecanoylphorbol-13-acetate suggests that pancreatic islets may be a useful model with which to study the mechanisms of action of this and other tumor-promoters.