Studies of the functional and morphologic status of islets maintained at 24 C for four weeks in vitro.

Isolated rat islets were maintained in vitro at 24 C for 1-4 weeks in tissue culture medium containing D-glucose (1.5 mg/ml). The rate of insulin release at 24 C remained stable for three weeks (2.2 muU/islet/hr) and decreased to 1.2 muU/islet/hr during the fourth week. Increasing the temperature from 24 C to 37 C at the end of 1, 2, 3, or 4 weeks produced a 5--7-fold increase in the rate of insulin release in the presence of glucose (1.5 mg/ml). This rate of secretion was comparable to control islets maintained at 37 C for 1--4 weeks. Light- and electron-microscopic studies revealed minimal central necrosis of large islets maintained at 24 C for 3 weeks. In contrast, extensive central necrosis was present in large islets maintained at 37 C for only 1 week. Degranulation of B cells occurred at 24 C with almost complete degranulation at 28 days. Regranulation occurred when the temperature was increased to 37 C. These findings indicate that isolated islets maintained at 24 C remain functionally and morphologically intact for 4 weeks. Initial studies have shown that maintenance of islets at 24 C for 1 week in conjunction with a single injection of antilymphocyte serum will produce marked prolongation of survival of islet allografts. The finding that isolated islets will survive for prolonged periods of time at 24 C should be of importance to future studies on islet transplatation, immune rejection, and investigations on hormonal release from islets maintained under these conditions.