Objective: Obesity-related insulin resistance is closely associated with visceral fat accumulation. Several adipocyte-secreted molecules have been implicated in the development of type 2 diabetes, among them, the recently discovered adiponectin and resistin proteins. Some of these adipocytokines are also present in the immune system, thus suggesting an intriguing functional connection.
Research methods and procedures: We determined adiponectin and resistin expressions in visceral (VAT) and subcutaneous adipose tissue of lean and obese Zucker (fa/fa) rats using reverse-transcription polymerase chain reaction. Moreover, we analyzed the variations after body-weight reduction in food-restricted obese rats.
Results: Resistin and adiponectin expression was significantly lower in VAT of genetically obese in comparison with lean rats; no differences were observed when subcutaneous adipose tissues of the same animals were compared. Weight loss resulted in an increase of adiponectin expression in VAT, whereas a further significant decrease in resistin mRNA level was observed. Resistin is also present and equally expressed in splenocytes of lean and obese rats.
Discussion: Adiponectin and resistin are down-regulated in VAT of obese rats. Adiponectin expression is restored to normal levels after body-weight reduction, supporting its link with obesity-related insulin resistance. On the contrary, the further decrease of resistin mRNA after weight loss does not support the hypothesis that resistin may play a causative role in insulin resistance in obese rats. Moreover, we demonstrated the presence of resistin in immunocompetent cells in both humans and rats, thus adding another factor to the list of molecules that adipose tissue shares with the immune system.