Weight loss following gastric bypass increases aldosterone reactivity to orthostatic stress in patients with obesity

Weight loss after gastric bypass is associated with blood pressure (BP) reduction. However, the precise role of the sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS) in this reduction remains unclear. We investigated the effect of RYGB-induced weight loss on the hemodynamic, hormonal and renal responses to an orthostatic stress induced by lower body negative pressure (LBNP). We conducted a monocentric study comparing response to LBNP (−30 mbar) in two groups of obese participants the first group underwent RYGB surgery (RYGB group) and the second group received lifestyle counselling (control group). We studied urinary sodium excretion, hemodynamic and hormonal responses before, during and 1 h after orthostatic stress induced by LBNP at three timelines: one month before planned RYGB (intervention group), and 3 and 12 months after the intervention. Thirty-seven adult participants were enrolled: 25 patients (72% women, age: 42.1 ± 10.5 years old, BMI 43.0 ± 5.1 kg/m²) in the RYGB group and 12 in control group (58% women, age: 44.8 ± 13.6 years old, BMI 43.3 ± 5.3 kg/m²). At 12 months, mean weight decreased from 126.3 ± 23.2 kg to 116 ± 20.7 kg in the control group and from 120.9 ± 19.4 kg to 78.6 ± 14.0 kg in the RYGB group (<i>p</i> value &lt; 0.01 between groups). During LBNP, the reduction in urinary sodium excretion (−1.98 mmol/h; CI95%: −3.72 to −0.30, <i>p</i> value = 0.02) and the increase in plasma aldosterone concentration (PAC; +9.94 pg/ml, CI 95%: 0.317–19.569, <i>p</i> value = 0.043) were more pronounced in the RYGB group. Our study suggests that weight loss induced by RYGB increases aldosterone responsiveness to orthostatic stress and enhances the sodium tubular response during orthostatic stress. NCT02218112