Insulin binding and glucose transport in adipocytes in neonatal streptozocin-injected rat model of diabetes mellitus

Abstract

The neonatal streptozocin (STZ)-injected rat (NSIR) model of diabetes mellitus resembles human non-insulin-dependent diabetes mellitus (NIDDM) with respect to abnormalities in insulin secretory responses. The suggestion that insulin deficiency leads to insulin resistance, a prominent feature of human NIDDM, led us to examine insulin binding and glucose transport in the NSIR during the development of hyperglycemia. Male Wistar rats were injected at 2 days of age with STZ (90 mg/kg i.p.) or vehicle alone. Mild insulin deficiency, reflected by minimally decreased fed plasma insulin concentrations, was apparent at 4 wk (mean +/- SE, control vs. NSIR, 2.32 +/- 0.19 vs. 1.75 +/- 0.21 ng/ml) and at 8 wk. Pancreatic insulin content was dramatically reduced in NSIR to 12 and 5% of control values at 4 and 8 wk, respectively (P less than .001). Fed plasma glucose concentrations increased in the NSIR between 4 and 5 wk and were significantly elevated at 8 wk (251 +/- 25 vs. 527 +/- 52 mg/dl, P less than .001). 125l-labeled insulin binding showed a progressive increase as a function of adipocyte volume in control and NSIR. Epididymal fat pad weights and adipocyte volumes were significantly decreased in the NSIR. Thus, insulin binding did not differ when expressed per cell number but was increased in NSIR when corrected for cell size (percent specific binding X 10(2), 8.49 +/- 0.96 vs. 11.56 +/- 1.08/microliter cell vol; P less than .05, all ages combined).(ABSTRACT TRUNCATED AT 250 WORDS)