[In vitro studies on the islands of Langerhans. XI. Insulin secretion and content of isolated islands of Langerhans in the Wistar rat under short term incubation and under organ culture conditions].

Insulin (IRI) secretion pattern of collagenase isolated islets from Wistar rats were investigated in a batch type incubation (60 min) and under organ culture conditions (up to 7 days) with different concentrations of glucose as stimulus. The B-cell response within 60 min of incubation was determined in Krebs-Ringer bicarbonate buffer with 1 mg/ml bovine serum albumin and 16 mM HEPES (KRB-HEPES) and compared with the hormone release in a culture medium (TC 199) containing 10% calf serum. Additionally the insulin content of islets before and after 7 days of culture was assayed radioimmunologically. In the presence of culture medium the insulin secretion was enhanced by 5.8 mM glucose whereas this glucose concentration does not stimulate the insulin secretion in KRB-HEPES. During organ culture the insulin secretion was identical in media with 1.0 and 5.8 mM glucose, respectively, but 15 mM glucose raised the hormon output more than 10-fold. The insulin content of islets, cultured for 7 days was decreased in the presence of 15 mM glucose up to 30% and in the presence of 5.8 mM glucose up to 13% of that of islets after isolation. The recovery rate of insulin calculated as the sum of secretion and content after cultivation at 15 mM glucose was higher than 100%, whereas the experiments in the presence of 1.0-5.8 mM glucose are characterized by a recovery rate of 25%. The results are discussed in connection with a altered intracellular breakdown of insulin in the B-cells.