Abstract P312: A Novel Selective Melanocortin-4 Receptor Agonist Attenuates Bradycardia and Hyperglycemia in Diabetic Rats
We previously demonstrated that functional brain melanocortin 3/4 receptors (MC3/4R) are required for leptin to exert its chronic cardiovascular and antidiabetic actions. To determine if chronic treatment with a selective MC4R agonist reduces blood glucose and prevents bradycardia in diabetic rats, we used a novel compound with high affinity to MC4R. Male 12-week-old Sprague-Dawley rats (n=5/group) were instrumented with telemetry probes for determination of mean arterial pressure (MAP) and heart rate (HR) 24-hrs/day and an intracerebroventricular (ICV) cannula was placed in the brain lateral ventricle for continuous infusion of the selective MC4R agonist PL6214 (2.5 μg/hr) or MTII (a non-selective MC3/4R agonist, 10 ng/hr) via osmotic minipump. Induction of diabetes caused hyperphagia (20±1 to 32±2 g), hyperglycemia (89±3 to 494±44 mg/dl) and bradycardia (-47 bpm). Chronic infusion of PL6214 for 11 days transiently reduced food intake which returned to diabetic values by day 6 after starting the infusions, whereas chronic infusion of MTII caused a reduction in food intake lasting only 3-4 days. PL6214 reduced blood glucose by 63% on day 2 and 16% by day 11 of infusion, and prevented further bradycardia induced by diabetes (-35±14 bpm on the last day of infusion). Chronic MTII infusion reduced blood glucose by 31% on day 2 and by day 6 glucose levels had already returned to values observed before treatment was started. MTII infusion did not attenuate the bradycardia (-99±13 bpm on the last day of infusion). Diabetes did not alter MAP, while the MC4R agonist increased MAP by 5±1 mmHg compared to control values. These results indicate that selective activation of MC4R agonist attenuates bradycardia and hyperglycemia in type 1 diabetes, and may provide a new strategy for treatment of diabetes. (P20GM104357, NHLBI-PO1HL51971, AHA-SDG5680016 and Palatin Technologies).