Reversible Impairment of Glucose-Induced Insulin Secretion in SHR/N-cp Rats: Genetic Model of Type II Diabetes

Abstract

The SHR/N-cp rat is a new genetically obese model for non-insulin-dependent diabetes mellitus. Expression of the diabetes is enhanced by a high-sucrose (54%) diet. After 4 wk on the diet, the cp/cp rats weigh significantly more than their +/? controls, have postprandial hyperglycemia (> 400 mg/dl), and are hyperinsulinemic, with immunoreactive insulin (IRI) levels 10- to 20-fold > controls. Total pancreatic IRI tends to be increased 1.6-fold in the cp/cp rats (although not significantly). There is no increase in pancreatic proinsulin content as a percent of total IRI. Studies of in vitro pancreatic function were carried out with the isolated nonrecirculating perfused pancreas method. The cp/cp rats (n = 10) showed impaired or absent IRI responses to 16.5 mM glucose, whereas +/? rats (n = 9) responded with classic biphasic curves. Comparison of insulin secreted in 20 min revealed a > 53% decrease in IRI secretion in cp/cp rats (P < .05). A paradoxical hypersecretion of IRI at glucose concentrations of 0–2.7 mM was noted in cp/cp but not lean rats, i.e., 1.8 ± 0.2 mU/min IRI in cp/cp rats vs. 0.04 ± 0.007 mU/min in +/? rats. Perfusion of pancreases for 45 min with buffers containing no glucose resulted in restoration of a normal biphasic IRI response to 16.5 mM glucose in the cp/cp rats, whereas response in the lean rats was markedly reduced. Brisk IRI responses to 10 mM arginine in buffers with no glucose also occurred in cp/cp but not +/? rats. Glucagon secretion was relatively suppressed in the cp/cp rats. These findings are similar to those reported in glucose-infused normal rats and suggest that hyperglycemia per se may be responsible for the impaired β-cell responses to glucose in cp/cp rats.