The onset and progression of pancreatic insulitis in the overt, spontaneously diabetic, young adult BB rat studied by pancreatic biopsy.

A specially developed clamping procedure permitted the easy, complication-free removal of splenic pancreas from rats. Using this biopsy procedure pancreatic tissue was removed from 50- to 90-day-old BB rats to study in a retrospective experimental design the time at which insulitis appears in BB rats, which develop acute, overt diabetes before the age of 120 days. Islets in biopsies taken 18-53 days before the onset of diabetes showed normal structure and were free from any mononuclear infiltrations. Biopsies removed between 2 and 9 days before onset of diabetes in contrast showed widespread insulitis. In five rats in which the biopsy preceded the manifestation of diabetes by 11-16 days, only a small number of pancreatic islets showed small focal mononuclear cell infiltrations. Most of the islets in these five rats had a normal histologic appearance. Thus the lesions within the islets develop rapidly starting about 2-3 wk before overt diabetes. As revealed by autoradiography, pancreatic beta-cells still surviving at the time of onset of diabetes show a modest increase in replicative activity. Replicative activity of mononuclear inflammatory cells also was observed, suggesting that their accumulation within the islet tissue may result in part from local replication.

Glucose stimulation of beta-cell DNA replication in the intact rat and in pancreatic islets in suspension culture. Effects of alpha-ketoisocaproic acid, dibutyryl cyclic AMP, and 3-isobutyl-1-methylxanthine in the in vitro system.

DNA replication in pancreatic beta-cells was compared in intact rats maintained hyperglycemic by continuous glucose infusion up to 10 days and in rat islets maintained in suspension culture in RPMI 1640 medium up to 12 days. Replicative activity was evaluated by counting the proportion of labeled beta-cell nuclei after injection or addition of [3H]thymidine. In both experimental systems, DNA replication initially was markedly stimulated by high glucose; then it subsided, even though high levels of glucose were maintained. Culture of pancreatic islets in suspension permitted the study of various treatments on beta-cell DNA replication. Alpha-ketoisocaproic acid, a nonglycolytic substrate for the beta-cell, stimulated DNA replication. 3-Isobutyl-1-methylxanthine (IBMX), in the presence of 4 mM glucose, was a potent stimulator. In many instances the proportion of labeled beta-cell nuclei in islets cultured with IBMX exceeded that obtained with 25 mM glucose. Dibutyryl-cyclic AMP stimulated DNA replication but was not as effective as IBMX. Although the effect of IBMX markedly decreased during the second week of culture, IBMX was much more effective than 25 mM glucose in maintaining DNA replication persistently above basal (4 mM glucose) levels.