A comparison of the effects of streptozotocin, N-methylnitrosourea and alloxan on isolated islets of Langerhans.

Isolated normal rat islets were pre-incubated with Streptozotocin (STZ), N-methylnitrosourea (MNU) or alloxan for 5, 10, 30 or 60 minutes at 0 degree C or 37 degrees C, and then were washed and incubated at 37 degrees C for 60 minutes with glucose (16.7 mM). Suppression of the insulinotropic response to glucose during incubation required 10 minutes of pre-incubation with the nitrosoureas whose effects were directly related to concentration and were temperature dependent. The suppressive effects of both nitrosoureas could be reduced or abolished by simultaneous addition to the pre-incubation media of nicotinamide, 2-deoxyglucose or 3-0-methyl-glucose, but were unaffected by reduced glutathione, glucosamine, N-acetylglucosamine or mannoheptulose. Unlike the nitrosoureas, alloxan was B-cytotoxic at 0 degree C. The effect of alloxan at 0 degree C was blocked by glutathione but not by glucose. The evidence in this study is inconsistent with the concept that the glucose moiety of STZ promotes entry and action of this nitrosourea in pancreatic islet cells. Secondly, it shows that the immediate B-cytotoxic action of alloxan differ from that of STZ or MNU and is not abolished by decrease in temperature.