Islet phosphoinositide hydrolysis and insulin secretory responses from prediabetic FA/FA ZDF rats

Abstract

The sequence of events that culminate in the development of diabetes in the fa/fa Zucker diabetic fatty (ZDF) rat is unclear. In the present series of experiments islets from 5 week old prediabetic fa/fa male rats were isolated and their phosphoinositide (PI) hydrolysis and insulin secretory responses compared to those obtained from lean nondiabetic age- and weight-matched control rats. Peak first and second phase insulin secretory responses to 20mM glucose averaged 77±10 (mean±SE, n=7) and 491±47 pg/islet/min from lean, nondiabetic control islets. The comparable responses from fa/fa prediabetic rat islets were significantly greater, 264±51 and 810±18 pg/islet/min, In a parallel fashion 3H-inositol efflux and inositol phosphate responses from prediabetic rat islets were also greater than comparable control responses. These findings demonstrate that significant increases in the phospholipase C-mediated hydrolysis of islet PI pools and insulin release in response to hypergiycemic stimulation can be detected prior to the emergence of diabetes in the fa/fa ZDF rat. These early changes in beta cell responsiveness to glucose may contribute to the hyperinsulinemia and subsequent insulin resistance characteristic of this animal model of non-insulin dependent diabetes mellitus. © 1995 by Academic Press. Inc.