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Am J Physiol Heart Circ Physiol 293: H1609-H1616, 2007. First published June 1, 2007; doi:10.1152/ajpheart.01338.2006
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Heart failure progression is accelerated following myocardial infarction in type 2 diabetic rats

Margaret P. Chandler,1 Eric E. Morgan,1 Tracy A. McElfresh,1 Theodore A. Kung,1 Julie H. Rennison,1 Brian D. Hoit,2 and Martin E. Young3

1Department of Physiology and Biophysics, Case Western Reserve University, Cleveland; 2Department of Medicine, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio; and 3United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas

Submitted 8 December 2006 ; accepted in final form 30 May 2007


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Clinical studies have shown a greater incidence of myocardial infarction in diabetic patients, and following an infarction, diabetes is associated with an increased risk for the development of left ventricular (LV) dysfunction and heart failure. The goal of this study was to determine if the progression of heart failure following myocardial infarction in type 2 diabetic (T2D) rats is accelerated compared with nondiabetic rats. Male nondiabetic Wistar-Kyoto (WKY) and T2D Goto-Kakizaki (GK) rats underwent coronary artery ligation or sham surgery to induce heart failure. Postligation (8 and 20 wk), two-dimensional echocardiography and LV pressure measurements were made. Heart failure progression, as assessed by enhanced LV remodeling and contractile dysfunction, was accelerated 8 wk postligation in the T2D animals. LV remodeling was evident from increased end-diastolic and end-systolic diameters and areas in the GK compared with the WKY infarcted group. Furthermore, enhanced LV contractile dysfunction was evident from a greater deterioration in fractional shortening and enhanced myocardial performance index (an index of global LV dysfunction) in the GK infarcted group. This accelerated progression was accompanied by greater increases in atrial natriuretic factor and skeletal {alpha}-actin (gene markers of heart failure and hypertrophy) mRNA levels in GK infarcted hearts. Despite similar decreases in metabolic gene expression (i.e., peroxisome proliferator-activated receptor-{alpha}-regulated genes associated with fatty acid oxidation) between infarcted WKY and GK rat hearts, myocardial triglyceride levels were elevated in the GK hearts only. These results, demonstrating enhanced remodeling and LV dysfunction 8 wk postligation provide evidence of an accelerated progression of heart failure in T2D rats.

contractile function; left ventricular remodeling; gene expression

THE PREVALENCE OF type 2 diabetes mellitus (T2D) is increasing at an alarming rate in the Western world and, with it, the frequency of diabetes-related heart failure (29). Epidemiological studies have shown there is a greater incidence of myocardial infarction (MI) and the subsequent development of heart failure in the diabetic population, with diabetes presenting as a coexisting condition in 20–35% of heart failure patients (16, 47). Although extensive clinical and experimental studies demonstrate a specific "diabetic cardiomyopathy" (22, 48) in the absence of myocardial injury or coronary artery disease, it is largely subclinical and manifests primarily as diastolic dysfunction (13) and abnormal energy substrate metabolism (increased myocardial fatty acid oxidation, lipid accumulation, and impaired carbohydrate metabolism and insulin action; see Ref. 52). However, following a MI, diabetic patients have a substantially increased risk for the development of left ventricular (LV) dysfunction and heart failure (16; 39), and diabetic patients with heart failure have a poorer prognosis than nondiabetic heart failure patients (34). Furthermore, there are no specific therapies aimed at treating the diabetic subpopulation of heart failure patients, and, although medical advances have improved the overall mortality from cardiovascular disease in the normal population, the same degree of risk reduction has not been evident in the diabetic population (21).

Experimental studies assessing the direct pathophysiological effects of diabetic cardiomyopathy have used primarily insulin-deficient (type 1) diabetic models (26, 53) with fewer studies having been conducted in non-insulin-dependent diabetic models (14, 32). Similarly, although several studies have examined the effects of coronary artery ligation-induced heart failure in type I diabetic animal models (33, 45), few studies have systematically explored the effects of T2D on the development and progression of heart failure following myocardial injury. The present study was designed to determine whether the progression of heart failure following coronary artery ligation surgery is accelerated in the T2D milieu. We studied a nonobese animal model of T2D, the Goto-Kakizaki (GK) rat, previously developed by repeated inbreeding of glucose-intolerant Wistar rats and used by numerous investigators to investigate a variety of pathological processes associated with T2D (7, 11, 12, 14, 28, 35, 38). Studies were performed using the well-established rat infarct model of heart failure (41) with measurements of LV function and chamber remodeling and metabolic adaptations made 8 and 20 wk following coronary artery ligation or sham surgery in GK and Wistar-Kyoto (WKY) rats.


   MATERIALS AND METHODS
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 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Surgical procedures and study protocol. This study was conducted in accordance with the Guide for the Care and Use of Laboratory Animals (NIH publication Number 85-23) and with the approval of the Institutional Animal Care and Use Committee at Case Western Reserve University. These studies and all data interpretation were conducted with investigators blinded to each animal's group assignment. Animals were maintained on a reverse 12:12-h light-dark cycle (i.e., lights on at 7:00 P.M.), and all echocardiographic measures, surgical procedures, and tissue harvests were performed in the fed state 3–6 h after entering the dark phase (i.e., 10:00 A.M. to 1:00 P.M.). It has been established that the myocardial content of mRNA for metabolic genes plateaus during this time period (50). Some data for 8- and 20-wk WKY rats have been recently published (36) with the exception of biventricular mass-to-body mass ratio, end diastolic and end systolic diameters, plasma glucose and insulin, tissue triglyceride (TG), and all of the mRNA expression data. The previously published data are included strictly for the purpose of direct comparison between diabetic and nondiabetic animals.

Studies were conducted using 91 male nondiabetic WKY rats and T2D GK rats. Heart failure was induced by coronary artery ligation, as recently described (2, 36, 37, 44). Briefly, rats were anesthetized with 1.5–2.0% isoflurane, intubated, and ventilated. In 47 rats (WKY = 21 and GK = 26), a MI was induced by ligation of the left coronary artery. Sham animals (WKY = 21 and GK = 23) were subjected to the same surgical procedure without coronary artery ligation. Sham and infarcted rats were then randomly assigned to either an 8-wk (WKY sham = 11; ligation = 11; GK sham = 11; ligation = 13) or 20-wk postinfarction (WKY sham = 10; ligation = 10; GK sham = 12; ligation = 13) study group. The mean age of the 8-wk groups and the 20-wk groups was not different at the time of death (Table 1). Echocardiography was performed 8 wk after sham/ligation surgery for all groups and again 20 wk postinfarction for the 20-wk groups. Terminal surgical studies were conducted 2 days after the 8- or 20-wk echo studies where rats were anesthetized with 1.5–2% isoflurane and the LV was catheterized using a 3.5-Fr pressure transducer (Millar Instruments) introduced via the right carotid artery. Heart rate (HR), maximum LV pressure (LVP), peak end-diastolic pressure (EDP), peak ±dP/dt, and the time constant of isovolumic LV relaxation ({tau}) were recorded using a Digi-Med Heart Performance Analyzer-{tau} over a 30-s period. At the end of the hemodynamic measurements, the chest was opened by thoracotomy; 3 ml of blood were drawn from the inferior vena cava for plasma measurements; the LV, right ventricle (RV), and scar were quickly removed and weighed; and the LV was freeze-clamped and stored at –80°C.


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  		Table 1. Body and heart mass in WKY and GK rats 8- and 20-wk postcoronary artery ligation surgery to induce HF

 
Echocardiography. LV function was evaluated by echocardiography using a Sequoia C256 System (Siemens Medical) with a 15-MHz linear array transducer as previously described (37). Briefly, the rats were anesthetized with 1.5–2.0% isoflurane by mask, the chest was shaved, the animal was situated in the supine position on a warming pad, and electrocardiogram limb electrodes were placed. Two-dimensional guided M-mode and Doppler echocardiographic studies of aortic and transmitral flows were performed from parasternal and foreshortened apical windows. Study duration was typically 15–20 min/animal. All data were analyzed offline with software resident on the ultrasound system. End-diastolic and end-systolic dimensions (EDD and ESD) and {tau} were measured, and fractional shortening, myocardial performance index, and cardiac index were calculated as previously described (37).

Metabolic measurements. Plasma glucose, free fatty acids (FFA), and TG were measured using commercially available enzymatic spectrophotometric kits (Wako Chemicals, Richmond, VA). Plasma insulin was measured by ELISA (ALPCO). Myocardial tissue samples were pulverized in a stainless-steel tissue pulverizer cooled in liquid nitrogen. Myocardial activities of medium chain acyl-CoA dehydrogenase (MCAD) and citrate synthase (CS) were measured spectrophotometrically, and tissue TG content was measured from homogenate extracts using enzymatic spectrophotometer methods (5). C16-ceramide content in the LV was measured by gas chromatography with a flame ionization detector using C17-ceramide as an internal standard, as previously described (54). All tissue values are expressed per gram wet weight of tissue.

RNA extraction and quantitative RT-PCR. RNA extraction and quantitative RT-PCR was performed on frozen powdered LV tissue samples using previously described methods (10, 17, 23). Specific quantitative assays were designed from rat sequences available in GenBank for atrial natriuretic factor (anf), brain natriuretic peptide (bnp), skeletal {alpha}-actin (sk{alpha}-actin), peroxisome proliferator-activated receptor-{alpha} (ppar{alpha}), retinoid X receptor {alpha} (rxr{alpha}), citrate synthase (cs), medium chain acyl-CoA dehydrogenase (mcad), muscle-specific carnitine palmitoyltransferase 1 (mcpt1), pyruvate dehydrogenase kinase 4 (pdk4), uncoupling protein 3 (ucp3), mitochondrial thioesterase 1 (mte1), and uncoupling protein 2 (ucp2). Primer and probe sequences for these Taqman assays have been published previously (49, 55, 56), with the exception of bnp. Sequences for bnp are 5'-CAGAAGCTGCTGGAGCTGA-3' (forward primer), 5'-AGGGCCTTGGTCCTTTGAG-3' (reverse primer), and 5'-FAM-AGAGAAAAGTCAGAGGAAATGGCTCAGAGACA-TAMRA-3' (probe). Standard RNA was made for all assays by the T7 polymerase method (Ambion, Austin, TX), using total RNA isolated from rat hearts. The correlation between the Ct (the number of PCR cycles required for the fluorescent signal to reach a detection threshold) and the amount of standard was linear over at least a 5-log range of RNA for all assays. To control for sample-to-sample differences in RNA concentration, the level of transcripts for 18S was quantitatively measured in each sample. Expression of 18S was not different among the experimental groups (data not shown); therefore, the PCR data are reported as the number of transcripts per number of 18S molecules.

Assessment of infarct size. Previous studies investigating the extent of injury following MI in diabetic myocardium have been controversial, with results demonstrating both greater sensitivity to ischemic injury (33, 40) and an improved tolerance or protective effect of diabetes on myocardial injury (31). To eliminate infarct size as a confounding variable to the progression of heart failure in this study, we conducted a small supplementary study to examine the effects of T2D on infarct size in this rat model. Sixteen rats (8 WKY and 8 GK rats) underwent coronary artery ligation surgery to induce heart failure. Later (8 wk), hearts were extracted during termination surgery and preserved with 4% buffered formaldehyde solution after removal of the atria and RV. Each ventricle was sliced (~2 mm) perpendicular to the long axis and mounted between glass plates at a uniform thickness. Slices were photographed using a high-resolution camera (4 megapixels), and files were downloaded for planimetry measurements. The degree of infarction in each LV was determined by using the shareware program Image Tool (Image Tool for Windows 2.00; University of Texas Health Science Center, San Antonio, San Antonio, TX). The total area and the endomyocardial circumference of each of the LV slices was measured. The infarcted area was identified as that area of the wall that had experienced a significant reduction (>75%) in wall thickness, i.e., thinned relative to the surrounding tissue. Similarly, the total area of the infarct and the length of the endomyocardial circumference contained within the infarct zone were also measured. The infarct size was expressed as a percent of both the total endomyocardial circumference and the total LV area.

Statistical analysis. Data are expressed as group means ± SE. Comparisons between the WKY and GK and sham and ligation surgeries at 8 and 20 wk were compared by three-way ANOVA followed by Bonferroni t-test for multiple comparisons. When comparisons were made between the two strains and sham vs. ligation at 20 wk, a two-way ANOVA was used followed by Bonferroni t-test for multiple comparisons. For all statistical analysis, significance was accepted at P < 0.05.


   RESULTS
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
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Mortality rates and infarct size. Mortality rate following coronary artery ligation surgery did not differ between GK and WKY rats (29 ± 8 vs. 34 ± 4%, respectively). The infarct size 8 wk following ligation surgery expressed as a percent of both the total endomyocardial circumference (24 ± 4 vs. 24 ± 4%) and the total LV area (19 ± 3 vs. 20 ± 3%) did not differ between GK and WKY rats, respectively.

Body and ventricular mass. GK sham and infarcted rats had significantly lower body mass than their respective WKY control groups at both 8 and 20 wk (P < 0.05). Body mass was not significantly altered by the infarction in either GK or WKY groups relative to their sham control. LV and RV masses were both significantly lower in GK rats compared with WKY rats. Induction of heart failure increased RV mass and total LV and RV mass-to-body mass ratios in both GK and WKY rats at 8 and 20 wk (Table 1). The mean scar-to-LV mass ratio was similar for GK and WKY infarcted hearts. Biventricular mass-to-body mass ratio was significantly greater in all infarcted rats compared with their respective sham controls. Differences in biventricular-to-body mass ratio between GK and WKY sham at 8 and 20 wk may be secondary to the significant strain effect for lower absolute body mass.

Metabolic measurements. Plasma glucose and FFA were significantly higher in GK rats compared with WKY rats at both 8 and 20 wk (Table 2), whereas plasma TG was higher only at 20 wk. Myocardial tissue TG was not different between GK and WKY sham groups. Infarction had no significant effect on plasma substrates (glucose, FFA, and TG); however, tissue TG were elevated in GK infarcted hearts compared with GK sham hearts at both 8 and 20 wk. Interestingly, C16-ceramide content was significantly elevated by the infarction in both GK and WKY rat hearts compared with their respective sham groups at 20 wk, with no difference between the GK and WKY infarcted groups (data not shown). Nonfasting plasma insulin concentrations were significantly lower in GK rats compared with WKY rats and were lowered further following infarction.


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  		Table 2. Plasma and tissue substrates and enzyme activities in WKY and GK rats at 8- and 20-wk postligation surgery

 
There was a strain effect at 20 wk postinfarction in that CS activity was greater in the GK rats compared with the WKY rats, with the GK sham group having significantly greater activity than the WKY sham group. However, CS activity was significantly lower following infarction in all groups except the 20-wk WKY group. MCAD activity was not different between the GK and WKY rats but was lower following infarction in the 8-wk groups (Table 2).

Cardiac function. There were no significant differences in HR, peak LVP, and peak negative (–) dP/dt between the GK and the WKY sham groups. There were strain differences at 8 wk in EDD and at 20 wk in EDD and EDP between the GK and WKY groups. Coronary artery ligation did not affect HR or peak LVP, although peak EDP, EDD, ESD, and {tau} were elevated and peak +dP/dt, -dP/dt, area of fractional shortening, and cardiac index were reduced by infarction in all GK and WKY infarcted groups (Table 3). However, markers of contractile dysfunction in infarcted GK rats were accelerated 8 wk postligation, as evidenced by significant increases in end-diastolic diameter and area, end-systolic diameter and area, myocardial performance index, and greater deterioration in fractional shortening compared with infarcted WKY rats when expressed as a ratio of their corresponding sham groups (Fig. 1).


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  		Table 3. Functional assessments by echocardiography and LV cannulation in WKY and GK rats at 8- and 20-wk postligation surgery

 

Figure 1
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  		Fig. 1. Eight- and 20-wk echocardiography data for the 20-wk Wistar-Kyoto (WKY) and Goto-Kakizaki (GK) heart failure groups expressed as a ratio of their respective sham groups. *P < 0.05, 8 wk GK vs. 8 wk WKY groups.

 
mRNA expression. We examined the effects of T2D and infarction on the mRNA levels of anf, bnp, and sk{alpha}-actin (all markers of hypertrophy and heart failure), ppar{alpha}, rxr{alpha}, cs, and ucp2, as well as PPAR{alpha}-regulated genes that promote fatty acid oxidation, including mcad, mcpt1, pdk4, mte1, and ucp3. mRNA expression was normalized to the gene 18S, which did not differ among groups. There was a strain effect for cs, a mitochondrial marker enzyme, in that cs was elevated at both 8 and 20 wk in GK rats compared with WKY rats (Table 4). Expression of anf (expressed relative to their respective sham group) and sk{alpha}-actin were significantly greater in GK infarcted hearts compared with the WKY infarcted hearts at 8 and 20 wk (sk{alpha}-actin only; Fig. 2). The expression of bnp was elevated at 8 and 20 wk following infarction, whereas rxr{alpha} and the PPAR{alpha}-regulated genes mcad, pdk4, mte1, and ucp3 were reduced following infarction in both GK and WKY groups at 20 wk (treatment effect; Table 4). mRNAs encoding for ppar{alpha}, ucp2, and mcpt1 were not significantly affected by infarction.


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  		Table 4. mRNA expression in 8- and 20-wk WKY and GK sham and HF groups normalized to 18S (mol mRNA/mol 18S mRNA)

 

Figure 2
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  		Fig. 2. mRNA levels (normalized to 18S) for atrial natriuretic factor (anf) and skeletal {alpha}-actin (sk{alpha}-actin) in the heart failure groups expressed as a percentage of the mean value for their respective sham group. P < 0.05, main effect for strain GK vs. WKY (*), GK 8 wk vs. WKY 8 wk ({dagger}), and 20 wk WKY vs. 8 wk WKY ({ddagger}).

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The present study investigated whether the progression of heart failure following coronary artery ligation in T2D is accelerated compared with nondiabetic animals. Heart failure progression in the diabetic group was accelerated 8 wk postligation, as evidenced by significant increases in end-diastolic diameter and area, end-systolic diameter and area, and myocardial performance index and greater deterioration in fractional shortening compared with the nondiabetic heart failure group. This accelerated progression was accompanied by greater increases in mRNA expression of anf and sk{alpha}-actin, gene markers of heart failure and hypertrophy. Despite similar decreases in metabolic gene expression (i.e., PPAR{alpha}-regulated genes associated with fatty acid oxidation) between infarcted WKY and GK rat hearts, myocardial TG levels were elevated in the GK hearts only. These results support the concept of an accelerated progression in the early stages of heart failure in T2D rats.

Heart failure progression in the diabetic group was accelerated 8 wk postligation, as evidenced by enhanced LV remodeling and contractile dysfunction in the T2D heart failure group. This enhanced early progression of heart failure in our diabetic rats is consistent with data reported in both clinical trials and animal studies examining the disease progression of heart failure in diabetic patients and animals following an acute MI (19, 46, 51). The MILIS study (51) compared the course of acute MI between diabetic and nondiabetic patients; impairment in LV function was observed more frequently in the diabetic patients in the immediate period following infarction; however, as reported in this study, the rates of long-term LV dysfunction were similar between the diabetic and nondiabetic patients. Similarly, studies using animal models of heart failure in the early stages following an acute MI reported significantly greater LV dilatation and cardiac hypertrophy and greater reductions in LV contractile function in diabetic compared with nondiabetic infarcted animals (19, 46). Although results from the survival and ventricular enlargement trial (42) reported that the increased incidence of heart failure after MI was not accompanied by greater LV enlargement and remodeling in diabetic patients, this study did not report remodeling results early in the progression of heart failure nor did they report progression in contractile dysfunction between the two populations of patients (47).

The observation that heart failure progression in the 8-wk diabetic group was accelerated, as evidenced by significant increases in LV remodeling and greater deterioration in fractional shortening, was not simply the result of differences in infarct size, since 8 wk following ligation surgery, infarct size did not differ between GK and WKY rats. It is noteworthy that several additional patient and animals studies have shown that, although diabetes is often associated with increased infarct size and risk of heart failure post-MI, the latter two parameters are not dependent on one another (45, 47). Our results are consistent with the idea that enhanced progression in the early stages of the development of heart failure is the result of the inherent diabetic cardiomyopathic processes evident in the GK rat and not the result of the severity of injury following ligation surgery.

It is becoming increasingly clear that metabolic remodeling is an integral and essential component of the remodeling process of the heart associated with various disease states, such as diabetes mellitus and ischemia. Recent studies have confirmed that changes in myocardial substrate utilization contribute significantly to myocardial contractile dysfunction in diabetes (1). Diabetes is known to be associated with altered myocardial substrate utilization, specifically increased fatty acid and decreased glucose utilization, and has been associated with an increase in the risk of heart failure. Numerous studies have clearly demonstrated that hearts from T2D animals exhibit LV dysfunction and altered metabolism of exogenous substrates (3, 27). Interestingly, though, correction of these diabetes-induced metabolic abnormalities (e.g., following treatment with a PPAR{gamma} agonist) has been shown to both improve (18) or have no effect (4) on LV contractile function.

When fatty acid availability exceeds the rate of fatty acid utilization, fatty acid derivatives accumulate within the cell. The latter is associated with the pathogenesis of beta-cell dysfunction, insulin resistance, and diabetic cardiomyopathy (15, 22, 25). Numerous studies have also shown that elevations in myocardial TG and other lipotoxic intermediates, such as ceramide, are associated with cardiac contractile dysfunction, LV remodeling, and apoptotic cell death, and that this contractile function can be prevented and/or reversed by the reduction of these toxic lipid intermediates (8, 9, 30, 57). Specifically, studies in obese Zucker diabetic fatty rats (57) and acyl-CoA-overexpressing transgenic mice (8, 9, 30) have demonstrated that overaccumulation of myocardial TG is associated with dilated cardiomyopathy accompanied by profound impairment of systolic function, elevated ceramide content, and increases in markers of apoptosis (myocardial DNA laddering and cytochrome c release), which together are indicative of severe lipotoxic cardiomyopathy. As such, cells have evolved mechanisms to balance fatty acid availability with fatty acid utilization. For example, the heart increases rates of both fatty acid oxidation and TG export in the type I diabetic milieu (3, 24). Similarly, the role of hyperleptinemia as a protective measure against steatosis and lipotoxicity has been clearly demonstrated during dietary-induced obesity (30). The present study reports that, although plasma FFA levels are elevated in GK rats, myocardial TG levels are normal (i.e., identical to WKY rats). However, consistent with previous studies suggesting fatty acid oxidation rates are reduced in failing hearts, the current study reports that coronary artery ligation results in a repression of genes promoting fatty acid oxidation in both WKY and GK rat hearts. Interestingly, this is associated with increased myocardial TG levels in infarcted GK rat hearts only. Thus coronary artery ligation appears to imbalance fatty acid availability and fatty acid utilization in the T2D milieu.

Numerous studies have proposed other possible underlying mechanisms to account for enhanced early progression of heart failure during T2D. Diabetic heart failure following an MI has been associated with increased myocardial oxidative stress, which in turn could explain the depressed contractile performance in diabetic animals. Studies have demonstrated augmentation of oxidative stress in the surviving tissues of diabetic rat hearts following MI, concomitant with an increased severity of heart failure (46). Alternatively, adult GK rats have also been shown to have defective myocardial blood flow associated with altered LV contractile function, which could allude to a possible role for microvascular abnormalities in the enhanced progression of heart failure in this model (28).

Although data from the literature have reported that the GK rat is characterized as both mildly hyperinsulinemic (7) and normoinsulemic (35), our animals had significantly lower plasma insulin concentrations compared with the nondiabetic controls, with moderate reductions following the induction of heart failure in the WKY group. These results are in sharp contrast to studies using other rodent models of T2D (e.g., the db/db mouse and the Zucker diabetic fatty rat), which are characterized as being hyperinsulinemic (3, 6, 18, 19). However, postprandial insulin levels in our GK rats are comparable to other studies where adult GK rats had significantly lower insulin levels compared with nondiabetic Wistar rats (20, 35). Chronic elevations in plasma glucose may be responsible, in part, for beta-cell desensitization to glucose, which could account for the lower plasma insulin levels (43). Furthermore, a number of studies have reported decreases in total pancreatic insulin stores and beta-cell mass in GK rats, resulting in a decreased in vivo insulin secretory response to glucose that may also contribute to the lower plasma insulin levels reported in our GK groups (38, 43). This decreased insulin secretory response to glucose may also reflect alterations in pancreatic beta-cell function because of the established potent lipotoxic effects (25) of high plasma and tissue fatty acids that are characteristic of the GK rat.

In conclusion, heart failure progression in the diabetic group was accelerated 8 wk postligation, as evidenced by significant increases in LV remodeling and greater deterioration in contractile function compared with the nondiabetic heart failure group. This accelerated progression was accompanied by greater increases in mRNA expression of anf and sk{alpha}-actin, gene markers of heart failure and hypertrophy. These results support the concept of an accelerated progression in the early stages of heart failure in T2D rats.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by Diabetes Association of Greater Cleveland Grant no. 482-03 (M. P. Chandler) and American Heart Association Scientist Development Grant no. 0535361N (M. P. Chandler).


   ACKNOWLEDGMENTS
 
We thank David J. Durgan (Baylor College of Medicine) for assistance with mRNA isolation and real-time quantitative-PCR procedures.


   FOOTNOTES
 

Address for reprint requests and other correspondence: M. P. Chandler, Dept. of Physiology and Biophysics, School of Medicine, Case Western Reserve Univ., 10900 Euclid Ave., Cleveland, OH 44106-4970 (e-mail: mpc10{at}case.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

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