Peripheral insulin resistance develops in transgenic rats overexpressing phosphoenolpyruvate carboxykinase in the kidney

Abstract

Aims/hypothesis. To study the secondary consequences of impaired suppression of endogenous glucose production (EGP) we have created a transgenic rat overexpressing the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in the kidney. The aim of this study was to determine whether peripheral insulin resistance develops in these transgenic rats. Methods. Whole body rate of glucose disappearance (R d ) and endogenous glucose production were measured basally and during a euglycaemic/hyperinsulinaemic clamp in phosphoenolpyruvate carboxykinase transgenic and control rats using [6-3 H]-glucose. Glucose uptake into individual tissues was measured in vivo using 2-[1-14 C]-deoxyglucose. Results. Phosphoenolpyruvate carboxykinase transgenic rats were heavier and had increased gonadal and infrarenal fat pad weights. Under basal conditions, endogenous glucose production was similar in phosphoenolpyruvate carboxykinase transgenic and control rats (37.4±1.1 vs 34.6±2.6 µmol/kg/min). Moderate hyperinsulinaemia (810 pmol/l) completely suppressed EGP in control rats (−0.6±5.5 µmol/kg/min, p<0.05) while there was no suppression in phosphoenolpyruvate carboxykinase rats (45.2±7.9 µmol/kg/min). Basal R d was comparable between PEPCK transgenic and control rats (37.4±1.1 vs 34.6±2.6 µmol/kg/min) but under insulin-stimulated conditions the increase in R d was greater in control compared to phosphoenolpyruvate carboxykinase transgenic rats indicative of insulin resistance (73.4±11.2 vs 112.0±8.0 µmol/kg/min, p<0.05). Basal glucose uptake was reduced in white and brown adipose tissue, heart and soleus while insulin-stimulated transport was reduced in white and brown adipose tissue, white quadriceps, white gastrocnemius and soleus in phosphoenolpyruvate carboxykinase transgenic compared to control rats. The impairment in both white and brown adipose tissue glucose uptake in phosphoenolpyruvate carboxykinase transgenic rats was associated with a decrease in GLUT4 protein content. In contrast, muscle GLUT4 protein, triglyceride and long-chain acylCoA levels were comparable between PEPCK transgenic and control rats. Conclusions/interpretation. A primary defect in suppression of EGP caused adipose tissue and muscle insulin resistance. [Diabetologia (2003[Diabetologia ( ) 46:1338[Diabetologia ( -1347

A primary defect in glucose production alone cannot induce glucose intolerance without defects in insulin secretion

“…5 mBq/min in 0 . 9% saline for the duration of the experiment (155 min in total) as previously described by our laboratory (Lamont et al 2003, Visinoni et al 2008.…”

“…Basal turnover, hyperinsulinaemic/euglycaemic clamps and glucose uptake into peripheral tissues Basal turnover (nZ10 PVG/c; nZ8 PEPCK), hyperinsulinaemic/euglycaemic clamps (nZ5-6 PVG/c; nZ4-6 PEPCK) and peripheral glucose uptake into individual tissues under clamp (nZ5-6 PVG/c; nZ4-6 PEPCK) conditions were performed in subgroups of PVG/c control and PEPCK transgenic rats following an overnight fast as previously described by our laboratory and others (Kraegen et al 1991, Nolan & Proietto 1994, Lamont et al 2003. For the hyperinsulinaemic/euglycaemic clamp, insulin (Actrapid, Novo Nordisk, Bagsvaerd, Denmark) was infused during the clamp at a dose of 2 mU/kg for PEPCK transgenic rats and 4 mU/kg for PVG/c control rats as previously reported (Lamont et al 2003) to produce similar plasma insulin concentrations in the two groups of rats.…”

“…For the hyperinsulinaemic/euglycaemic clamp, insulin (Actrapid, Novo Nordisk, Bagsvaerd, Denmark) was infused during the clamp at a dose of 2 mU/kg for PEPCK transgenic rats and 4 mU/kg for PVG/c control rats as previously reported (Lamont et al 2003) to produce similar plasma insulin concentrations in the two groups of rats. Blood glucose was maintained at euglycaemia with a 5% glucose solution.…”

“…To determine whole-body glucose turnover, plasma samples collected at 90, 100 and 110 min were treated, processed and measured for the level of H]glucose radioactivity as previously described by our laboratory (Nolan & Proietto 1994, Lamont et al 2003. Briefly, a 25 ml aliquot of plasma was treated with equal volumes of 0 .…”

“…Whether defects in both insulin action and secretion are necessary for glucose intolerance to develop is still debatable (Valera et al 1994, Trinh et al 1998, Sun et al 2002, Visinoni et al 2008. We have previously hypothesised that a primary defect in the suppression of gluconeogenesis (GNG) resulting in inappropriately elevated endogenous glucose production (EGP; Lamont et al 2003), will cause glucose intolerance and fasting hyperglycaemia, as observed in T2D (Consoli et al 1989, Nurjhan et al 1992, Perriello et al 1997, Boden et al 2001. Although GNG occurs predominantly in the liver, it has been suggested that the kidney accounts for w40% of overall GNG (Stumvoll et al 1998, Cersosimo et al 2000, Gerich et al 2001.…”