Review Question - QID 100073

A 38-year-old woman presents to her primary care physician for her yearly exam. Her only complaint is difficulty losing weight. Her BMI is 34 kg/m^2. In addition to a standard physical exam, the physician orders a glucose tolerance test. The woman's fasting blood glucose level is 120 mg/dL and two-hour post 75g glucose load blood glucose level is 190 mg/dL. The physician informs the patient that she is "pre-diabetic" or at risk of developing diabetes and recommends lifestyle modification with follow-up in 6 months. Which of the following endogenous signaling molecules or receptors will increase insulin sensitivity in this patient?