Moderate Weight Loss Reduces Renin and Aldosterone but does not Influence Basal or Stimulated Pituitary-adrenal Axis Function

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Abstract
Body fat mass and nutrition influence secretion of the adrenocortical hormones - aldosterone and cortisol - via several mechanisms. However, there are no data on adrenocortical function following widely prescribed mild diet-induced weight loss (10%) in obese subjects. In the present study, 25 healthy obese volunteers (BMI 32.9±4.3 kg/m2) followed a 30% calorie restricted diet over 12 weeks. Hypothalamic-pituitary-adrenal (HPA) axis function was assessed by 24-hour urine free cortisol/cortisone and a 1 mcg ACTH stimulation test with measurement of total and free cortisol and corticosteroid-binding globulin (CBG). The renin-angiotensin-aldosterone system (RAAS) was assessed by measurement of plasma aldosterone and renin under salt depleted (30 mmol/d) and loading (250 mmol/d) conditions. Volunteers’ weight fell by 8.5±0.8 kg (8.9±0.7%) and seated systolic blood pressure fell by 8.7±2.7 mm Hg and diastolic blood pressure by 7.0±1.4 mmHg (p<0.01). Plasma aldosterone and renin levels fell significantly with weight loss (aldosterone: 853±156-635±73 pmol/l; renin: 35.4±7-24±3 mU/l, both p<0.05). The volunteers were relatively salt insensitive (mean arterial pressure change with salt intake: 4 mmHg) and this was not affected by weight loss. Moderate weight loss had no effect on 24-hour urine free cortisol/cortisone, or on basal, or ACTH-stimulated free and total cortisol, or CBG. Hence this conventional weight loss program reduces blood pressure and activity of the RAAS via an effect on renin release. Despite various described influences of fat mass and energy restriction on HPA axis function, there were no changes in basal and stimulated HPA axis function with moderate weight loss. There may be a threshold effect of weight loss/energy restriction required to alter HPA axis function, or moderate weight loss may lead to a counterbalanced effect of stimulatory and inhibitory influences on HPA axis function.