Increased glucagon-stimulated insulin secretion of cryopreserved rat islets transplanted into nude mice

Cryopreservation is the only available technique for long-term storage of p ancreatic islets. The freezing/thawing protocol may cause considerable loss of viable islet tissue and impair its function in vivo. The aim of this st udy was to investigate glucose and insulin levels after transplantation of fresh and cryo/thawed rat islets. Rat pancreatic islets were isolated follo wing intraductal collagenase injection and Ficoll gradient purification. Af ter isolation, islets were cultured for 24 h and then either transplanted o r frozen after stepwise addition of DMSO according to Rajotte et al. and st ored in liquid nitrogen. After rapid thawing islets were stepwise transferr ed into RPMI medium and cultured for another 24 h. The recipients were athy mic mice with streptozotocine-induced diabetes. Two hundred fresh (n=13) or cryo/thawed (n=15) islets were transplanted beneath the renal capsule. Glu cose levels were measured for 14 days and blood samples for insulin determi nation were obtained 15 min after i.p. glucagon (10 mg/kg) administration o n day 14. Glucose levels were normalized (<9 mmol/l) in all recipients with in 3 days since transplantation. On day 14, mean fasting values+/-SE in fre sh and cryo/thawed islet groups were 4.0+/-0.6 and 4.4+/-0.4 mmol/l, respec tively (P>0.05). Fasting insulin levels were higher in the cryo/thaw than i n the fresh islet group (1.67+/-0.33 vs 0.57+/-0.13 ng/ml; P<0.01). Post-gl ucagon levels did not differ significantly (1.45+/-0.24 vs 0.86+/-10.24 ng/ ml; P=0.06). While glucagon significantly increased insulin levels (P<0.01) in the fresh islet group, no change in insulin levels was observed (P>0.05 ) in the cryo/thaw group. Immunohistochemical staining demonstrated fragmen tation of viable islet tissue which was more apparent in the cryo/thaw grou p. We conclude that in a short-term study cryo/thawed rat islets produce hi gher insulin levels than fresh islets transplanted into nude mice. This may be due to better islet survival or loss of feed-back regulation.