Metallothionein in isolated pancreatic islets of mice: Induction by zinc and streptozotocin, a naturally occurring diabetogen

Metallothionein (MT) concentrations were determined in the cytosol of isolated pancreatic islets of mice, using both the cadmium (Cd)-heme and the Cd-Chelex assay. Both constitutive MT levels and significant MT induction were detected in islet cells. For MT induction, mice were injected intraperitoneally (i.p.) with either zinc sulfate (Zn) or the diabetogen streptozotocin (STZ). Following an i.p. injection of 15 mg Zn-kg−1 body weight (body wt), the mean index of MT induction found in islets was comparable to that found in liver tissue, which was used as control. After i.p. injection of 30 mg Zn-kg−1 or a single high dose of STZ (100 or 200 mg·kg−1), the indices of MT induction in islets exceeded those in liver by a factor of 1.3, 2.5, or 1.5. After multiple low doses of STZ (3 or 5 x 40 mg·kg−1 given on consecutive days), in contrast, the MT induction indices in islets exceeded those in liver by a factor of 3.5 and 3.9 for 3×40 respectively 5×40 mg STZ· kg−1. In conclusion, our results demonstrate constitutive MT levels in isolated pancreatic islets and significant MT induction after i. p. injection with Zn or STZ, in particular after repeated low doses of STZ.