Abstract 439: Role of Hindbrain Endogenous Melanocortin Receptor Activity in Contributing to Hypertension in SHR

Abstract

We previously demonstrated that activation of the central nervous system (CNS) melanocortin system plays a key role in the modulation of sympathetic nerve activity (SNA) and blood pressure (BP) regulation. In the present study, we examined whether chronic inhibition of melanocortin-4 receptors (MC4R) in the hindbrain attenuates the elevated blood pressure in spontaneously hypertensive rats (SHR). The long-term cardiovascular and metabolic effects of MC4R antagonism were assessed in SHR and normotensive Wistar-Kyoto (WKY) rats. Male WKY rats (n=6) and SHR (n=7) were implanted with telemetry probes to measure BP and heart rate (HR) 24-hrs/day, and an intracerebroventricular (ICV) cannula was placed into the fourth ventricle (4 th V). After 10 days of recovery and 5 days of control measurements, the MC4R antagonist (SHU-9119, 1 nmol/h, 4 th V) was infused for 10 days followed by a 5-day recovery period. Chronic hindbrain MC4R antagonism significantly increased food intake and body weight in WKY (17±1 to 35±2 g/day and 280±8 to 353±8 g) and SHR (19±2 to 35±2 g/day and 323±7 to 371±11 g). No changes were observed in blood glucose levels (99±4 to 87±4 and 89±5 to 89±4 mg/dl, respectively for WKY and SHR). Chronic SHU-9119 infusion reduced MAP and HR similarly in WKY (-5±1 mmHg and -47±3 bpm) and SHR (-8±3 mmHg and -44±3 bpm). These results suggest that although hindbrain MC4R activity is important for appetite and HR regulation, it does not play a major role in mediating the elevated blood pressure in SHR. (NHLBI-PO1 HL51971/AHA SDG5680016)