The aim of this study was to explore the association between adiponectin (APN), APN receptors and insulin resistance (IR) using rats with type 2 diabetes mellitus (T2DM) as a model of diabetic cardiomyopathy (DC). Serum and cardiac APN levels were assessed using a double-antibody sandwich ELISA. In addition, the mRNA and protein expression of the myocardial APN receptor 1 (AdipoR1) was determined using the reverse transcription polymerase chain reaction and immunohistochemical staining. The results showed that the heart weight/body weight ratio, fasting plasma glucose (FPG) and lipid levels, and the homeostasis model assessment-estimated IR (HOMA-IR) index were elevated in the T2DM group compared with the control group. Cardiac function was significantly lower in the T2DM group compared with the control group (P<0.05). Furthermore, serum and cardiac APN levels were significantly reduced in the T2DM group compared with the control group, and mRNA and protein expression of AdipoR1 was lower in the T2DM group compared with the control group (P<0.05). Changes in the morphology of myocardial cells were observed under the light microscope using hematoxylin and eosin staining. Myocardial cell hypertrophy, a disordered cell arrangement and irregular nuclear size were observed in the T2DM group. By contrast, myocardial cells in the control group were arranged in neat rows with uniform cytoplasmic and nuclear staining. According to the correlation analyses, serum APN levels in the T2DM group were negatively correlated with FPG, triglyceride, total cholesterol and fasting insulin (FINS) levels, as well as with the HOMA-IR index. Myocardial AdipoR1 protein expression was positively correlated with myocardial APN levels, and negatively correlated with FINS and HOMA-IR. It may be concluded that myocardial and serum levels of APN are reduced in rats with DC. Metabolic disorders of blood glucose and lipid levels, as well as IR, are associated with low APN levels. Furthermore, low levels of myocardial Adipo1R mRNA and protein expression correlate with reduced insulin sensitivity.
Keywords: adiponectin; adiponectin receptor; diabetic cardiomyopathy.