INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEINS FROM ADULT-HAMSTER PANCREATIC-ISLETS - INFLUENCE OF GLUCOSE-CONCENTRATION

This study investigated the effect of glucose on insulin-like growth f actor binding proteins (IGFBPs) in islets isolated from pancreas of ad ult hamsters and compared the response pattern with that of their seru m IGFBPs. Serum samples and islets were obtained from adult normal mal e hamsters, and IGF-binding capacity was measured in aliquots of serum , sonicated islets, or conditioned medium using either I-125-hIGF-I or -II. IGFBPs were characterized in these samples by the ligand-blottin g technique, and insulin was measured in conditioned medium by radioim munoassay. Three IGFBP fractions were identified in serum, with relati ve molecular weights of 38, 30-33, and 24 kDa, while only two fraction s of 30-33 and 24 kDa were identified in islets or in their conditione d medium. Islets cultured with 2 or 16 mM glucose for 48 h released mo re insulin in the presence of the higher glucose concentration. The bi nding capacity measured in the islet suspension or conditioned medium increased as a function of glucose concentration in the incubation med ium. The IGFBPs present both in islets and conditioned medium had a 3- to 4-fold higher apparent affinity for IGF-II than IGF-I. The higher glucose concentration increased the intensity of the two IGFBP bands i dentified in the islet suspension by 2- to 3-fold. Our data show that two low-molecular-weight IGFBPs were released from adult hamster pancr eatic islets, with a different distribution pattern from that of hamst er serum, and that the amount of IGFBPs released by islets depended on the glucose concentration in the culture medium. Though not conclusiv e, these data suggest that IGFBPs may play a regulatory role in B-cell turnover in adult islets as they do in foetal islets.