Characterization of pseudo-islets formed from pancreatic islet cell suspensions of neonatal rats

Well-preserved pancreatic islet cell suspensions were prepared from islets of Langerhans of neonatal rats by gentle trypsin treatment. Within a culture period of 4-6 days the islet cells reaggregate spontaneously and form pseudo-islets of different size and of a variable insulin content. While the ratio of insulin to glucagon in isolated islets of Langerhans is constant (18 +/- 1.9), the hormone ratio of the pseudo-islets is strongly variable and increased, indicating an excess of insulin. Glucose enhancement from 1.5 mmoles/l to 15 mmoles/l results in a significant stimulation of (pro)insulin biosynthesis whereas insulin secretion of the pseudo-islets is only slightly increased. At high glucose concentration (15 mmoles/l) insulin secretion of the pseudo-islets can be potentiated (by a factor of 4.5 +/- 0.46) by 3-isobutyl-l-methylxanthine (IBMX). Compared with the initial islet cell suspension, the cell aggregation during pseudo-islet formation did not result in an enhanced secretory response on glucose stimulation.