ISLET AMYLOID POLYPEPTIDE IN PSAMMOMYS-OBESUS (SAND RAT) - EFFECTS OFNUTRITIONALLY INDUCED DIABETES AND RECOVERY ON LOW-ENERGY DIET OR VANADYL SULFATE TREATMENT

We investigated the possible relationship between islet amyloid polype ptide (IAPP) and the hyperinsulinemia and/or hyperglycemia that is see n in the desert-adapted gerbil Psammomys obesus, when the animal is tr ansferred from a low-energy (LE) diet to a high-energy (HE) diet. The effects of vanadyl sulfate and transition from a HE to a LE diet on th e diabetic state of the Psammomys were also studied. Psammomys maintai ned on a LE diet, showing normoinsulinemia and normoglycemia (group A) , were used as controls. IAPP and insulin immunoreactivity in the isle ts of Langerhans was studied using the peroxidase-antiperoxidase techn ique and plasma levels of the two hormones were determined by radioimm unoassays. The islet immunoreactivity of both IAPP and insulin was sig nificantly weaker in the hyperinsulinemic and hyperglycemic Psammomys (group C) compared to group A. Transfer to a LE diet resulted in compl ete recovery of the IAPP- and insulin-staining pattern to that seen in group A [group A-Rec (nutrition)]. The plasma IAPP levels of the grou p C animals were not significantly higher than in group A, while after vanadyl sulfate treatment the IAPP levels and IAPP/insulin ratios rem ained significantly higher [group A-Rec (vanadyl)]. At the same time t he circulating levels of glucose and insulin were restored to normal. Conclusively, islet IAPP and insulin immunoreactivity disappeared and reappeared in parallel in Psammomys transferred to a HE diet and back to a LE diet. Furthermore, vanadyl sulfate treatment of the hyperinsul inemic and hyperglycemic animals normalized circulating glucose and in sulin levels, but not IAPP levels, possibly due to a negative feedback effect of IAPP on insulin release.