Ghrelin is a
growth hormone-releasing peptide secreted by the stomach with potent effects on appetite. Experimental and clinical studies indicate that
ghrelin also influences cardiovascular regulation and metabolic function and mediates behavioral responses to stress. We investigated the effects of
ghrelin on blood pressure (BP), sympathetic nervous system activity, and mental stress responses in lean (n=13) and
overweight or obese (n=13) individuals. Subjects received an
intravenous infusion of human
ghrelin (5 pmol/kg per minute for 1 hour) and saline in a randomized fashion.
Ghrelin decreased systolic (-6 and -11 mm Hg) and diastolic BP (-8 mm Hg for both), increased muscle sympathetic nervous system activity (18±2 to 28±3 bursts per min, P<0.05 and from 21±2 to 32±3 bursts per min, P<0.001) in lean and
overweight or obese subjects, respectively, without a significant change in heart rate, calf blood flow, or vascular resistance.
Ghrelin induced a rise in plasma
glucose concentration in lean individuals (P<0.05) and increased
cortisol levels in both groups (P<0.05). Stress induced a significant change in mean BP (+22 and +27 mm Hg), heart rate (+36 and +29 bpm), and muscle sympathetic nervous system activity (+6.1±1.6 and +6.8±2.7 bursts per min) during saline infusion in lean and
overweight or obese subjects, respectively. During
ghrelin infusion, the changes in BP and muscle sympathetic nerve activity in response to stress were significantly reduced in both groups (P<0.05). In conclusion,
ghrelin exerts unique effects in that it reduces BP and increases muscle sympathetic nervous system activity and blunts cardiovascular responses to mental stress. These responses may represent a combination of peripheral (baroreflex-mediated) and central effects of
ghrelin.