Multiple abnormalities in insulin responses to nonglucose nutrients in neonatally streptozotocin diabetic rats

Abstract

Insulin responses to nutrient secretagogues were investigated in neonatally streptozotocin-injected (n-STZ) rats, i.e. an animal model of noninsulin-dependent diabetes. In the perfused pancreas 16 mM L-glutamine induced and 10 mM octanoate tended to induce (P less than 0.2) higher responses in n-STZ than in nondiabetic rats. Addition of 3.9 mM glucose potentiated responses to glutamine and octanoate more in n-STZ (3.3- and 3.4-fold) than in nondiabetic rats (1.5- and 1.9-fold). Conversely, the succinate derivative succinate monomethylester (Succ ME) induced lesser response in n-STZ rats (57% of that in nondiabetic rats) and coperfusion with 3.9 mM glucose increased the response less in n-STZ (1.4-fold) than in nondiabetic rats (3.8-fold). Pyruvate (20 mM) mimicked the potency of 3.9 mM glucose, i.e. pyruvate potentiated the response to Succ ME only nonsignificantly (1.2-fold) in n-STZ but markedly (4.9-fold) in nondiabetic rats. Dichloroacetate (20 mM) failed to affect the response to Succ ME together with pyruvate in n-STZ rats. To investigate the role of hyperglycemia for octanoate-induced secretion, nondiabetic rats were made hyperglycemic by 48-h glucose infusions. Octanoate-induced secretion from perfused pancreas was enhanced 3.8-fold after moderate hyperglycemia (13.2 +/- 0.6 mM) and 17-fold after marked hyperglycemia (22.7 +/- 0.6 mM). This positive association between response and degree of hyperglycemia was not found with a nonnutrient secretagogue, 3-isobutyl-1-methylxanthine. Results with glutamine and octanoate indicate that oxidation of nonglucose nutrients which normally do not regulate secretion is enhanced secondary to chronic hyperglycemia. Results with Succ ME and pyruvate suggest that early steps of oxidation of glucose are impaired in n-STZ rats.