Regulation of in vitro maturation of stimulus-secretion coupling in fetal rat islet beta-cells

We have studied the maturation of a glucose-responsive insulin release from fetal rat islets, and specifically investigated the im pact of nutrients, alpha-adrenoceptors, imidazoline receptors, and cyclic adenosine monophosph ate (cAMP), Islets were isolated from 21-d-old fetal rats and maintained fo r 7 d in tissue culture at 3.3 or 11.1 mM glucose and Various supplements. Culture in the presence of the nonglucidic nutrient alpha-ketoisocaproic ac id (KIC), markedly enhanced both basal and stimulated insulin release from islets cultured at either low or high glucose. Additionally, KIC significan tly elevated the insulin content of islets maintained in low glucose, where as it slightly lowered it in islets cultured at high glucose. Culture with phentolamine, an antagonist of alpha-adrenergic and imidazoline receptors, markedly amplified both basal and glucose-stimulated insulin secretion when added with islets cultured in either low or high glucose. By contrast, the pure alpha(2)-adrenoceptor antagonist benextramine had no such effects. Ad dition to culture media of a membrane-permeant agonist (Sp-cAMP[S]) or anta gonist (Rp-cAMP[S]) of cAMP-dependent protein kinases types I and II Failed to influence basal or glucose-responsive insulin secretory rates at either glucose concentration during culture as well as islet insulin content. In conclusion, islet beta-cell differentiation and functional maturation of th e stimulus-secretion coupling can be accelerated in vitro in fetal rat panc reatic tissue by nutrient stimulation, and by interference with imidazoline receptors, whereas cAMP seems virtually ineffective in this respect. These effecters may be of regulatory significance in the in vivo development of glucose-sensitive beta-cells.