Relationship between sympathetic reactivity and body weight loss in morbidly obese subjects

To investigate the possible role of peripheral sympathetic activity in gastric bypass-induced body weight loss.

In 42 morbidly obese patients (sex: 36 f/6 m; BMI: 46.0+/-0.7 kg/m(2)) undergoing a gastric bypass, the skin vasoconstrictor reflex in answer to a deep inspiration was measured by laser Doppler fluximetry. The extent of vasoconstriction, measured at the second finger of the left hand, was expressed as percent reduction of the basal blood flux (% vasoconstriction). Insulin sensitivity was assessed before surgery in a subset of patients (n=11), by the method of euglycemic, hyperinsulinemic clamp. Body weight and composition were evaluated before, and 3, 6 and 12 months after surgery. At the same time points, energy intake (kJ/day) was evaluated by means of both food record diary and alimentary anamnesis.

The % vasoconstriction, which was significantly (P=0.01) greater in normoglycemic subjects than in diabetic ones, was also significantly (P=0.03) related to the extent of insulin sensitivity measured during the euglycemic clamp. The % vasoconstriction showed a significant (P>0.0001), positive correlation with weight reduction obtained between the 6th and 12th months following surgery; as a consequence, % vasoconstriction was significantly (P=0.0004) related to the overall body weight loss achieved during the year following the operation. These correlations remained significant in multiple regression analysis with adjustment for age, initial body weight, plasma glucose and insulin (P=0.0007 and 0.006, respectively). The % vasoconstriction was also significantly (P=0.0006), negatively related to energy intake measured 12 months after surgery.

In conditions of stable body weight, the sympathetic nervous system (SNS) reactivity is influenced by the degree of insulin resistance. A high capacity to activate the SNS, measured before surgery, is associated with both a larger gastric bypass-induced weight loss and a lower energy intake, at the phase of weight stabilization.