Normal inhibition by somatostatin of glucose-stimulated B cell secretion in the obese subjects

Restored insulin inhibition on insulin secretion in nondiabetic severely obese patients after weight loss induced by bariatric surgery

OBJECTIVE

To examine the impact of important weight loss on insulin inhibition of its own secretion during experimentally induced hyperinsulinemia under euglycemic conditions.

DESIGN

Longitudinal, clinical intervention study--bariatric surgery (vertical banded gastroplasty--gastric bypass--Capella technique), re-evaluation after 4 and 14 months.

SUBJECTS

Nine obese patients class III (BMI=54.6+/-2.6 kg/m2) and nine lean subjects (BMI=22.7+/-0.7 kg/m2).

MEASUREMENTS

Euglycemic hyperinsulinemic clamp (insulin infusion: 40 mU/min m2), C-peptide plasma levels, electrical bioimpedance methodology, and oral glucose tolerance test (OGTT).

RESULTS

BMI was reduced in the follow-up: 44.5+/-2.2 and 33.9+/-1.5 kg/m2 at 4 and 14 months. Insulin-induced glucose uptake was markedly reduced in obese patients (19.5+/-1.9 micromol/min kg FFM) and improved with weight loss, but in the third study, it was still lower than that observed in controls (35.9+/-4.0 vs 52.9+/-2.2 micromol/min kg FFM). Insulin-induced inhibition of its own secretion was blunted in obese patients (19.9+/-5.7%, relative to fasting values), and completely reversed to values similar to that of lean ones in the second and third studies (-60.8+/-4.2 and -54.0+/-6.1%, respectively).

CONCLUSION

Weight loss in severe obesity improved insulin-induced glucose uptake, and completely normalized the insulin inhibition on its own secretion.

Lack of insulin inhibition on insulin secretion in non-diabetic morbidly obese patients

OBJECTIVE

Insulin inhibition of insulin secretion has been described in normal lean subjects. In this study, we examined whether this phenomenon also occurs in the morbidly obese who often have severe peripheral insulin resistance.

SUBJECTS

Twelve obese patients, normotolerant to glucose (8 F/4 M, body mass index (BMI)=54.8+/-2.5 kg/m(2), 39 y) and 16 lean control subjects (10 F/6 M, BMI=22.0+/-0.5 kg/m(2), 31 y).

DESIGN AND MEASUREMENTS

An experimental study using various parameters, including an euglycemic hyperinsulinemic clamp (280 pmol/min/m(2) of body surface), an oral glucose tolerance test (OGTT), electrical bioimpedance and indirect calorimetry.

RESULTS

The obese subjects were insulin resistant (M=19.8+/-1.6 vs 48.7+/-2.6 micromol/min kg FFM, P<0.0001) and hyperinsulinemic in the fasted state and after glucose ingestion. Fasting plasma C-peptide levels (obese 1425+/-131 pmol/l vs lean 550+/-63 pmol/l; P<0.0001) decreased less during the clamp in the obese groups (-16.9+/-6.9% vs -43.0+/-5.6% relative to fasting values; P=0.007). In the lean group, the C-peptide decrease during the clamp (percentage variation) was related to insulin sensitivity, M/FFM (r=0.56, P=0.03), even after adjustment for the clamp glucose variation.

CONCLUSION

We conclude that, in lean subjects, insulin inhibits its own secretion, and this may be related to insulin sensibility. This response is blunted in morbidly obese patients and may have a role in the pathogenesis of fasting hyperinsulinemia in these patients.

Somatostatin in eating disorders

Somatostatin concentrations in plasma were measured before and after a standardized fat and protein-rich fluid test meal in patients with anorexia nervosa, weight-recovered anorectic patients, obese women, and healthy controls. Somatostatin was significantly elevated in all four groups after the test meals. Hormone levels remained elevated for up to 100 min after the test meal. The area under the response curve was significantly higher (p < .01) in the anorectic patients as compared with healthy controls and weight-recovered anorectics. Obese women had blunted somatostatin responses. The findings may explain alterations in insulin secretion and in gastric emptying described earlier in patients with eating disorders.