Aerobic exercise training improves hepatic and muscle insulin sensitivity, but reduces splanchnic glucose uptake in obese humans with type 2 diabetes.

BACKGROUND: Aerobic exercise training is known to have beneficial effects on whole-body glucose metabolism in people with type 2 diabetes (T2D). The responses of the liver to such training are less well understood. The purpose of this study was to determine the effect of aerobic exercise training on splanchnic glucose uptake (SGU) and insulin-mediated suppression of endogenous glucose production (EGP) in obese subjects with T2D. METHODS: Participants included 11 obese humans with T2D, who underwent 15 ± 2 weeks of aerobic exercise training (AEX; n = 6) or remained sedentary for 15 ± 1 weeks (SED; n = 5). After an initial screening visit, each subject underwent an oral glucose load clamp and an isoglycemic/two-step (20 and 40 mU/m2/min) hyperinsulinemic clamp (ISO-clamp) to assess SGU and insulin-mediated suppression of EGP, respectively. After the intervention period, both tests were repeated. RESULTS: In AEX, the ability of insulin to suppress EGP was improved during both the low (69 ± 9 and 80 ± 6% suppression; pre-post, respectively; p < 0.05) and high (67 ± 6 and 82 ± 4% suppression, respectively; p < 0.05) insulin infusion periods. Despite markedly improved muscle insulin sensitivity, SGU was reduced in AEX after training (22.9 ± 3.3 and 9.1 ± 6.0 g pre-post in AEX, respectively; p < 0.05). CONCLUSIONS: In obese T2D subjects, exercise training improves whole-body glucose metabolism, in part, by improving insulin-mediated suppression of EGP and enhancing muscle glucose uptake, which occur despite reduced SGU during an oral glucose challenge.

Metabolic responses to exogenous ghrelin in obesity and early after Roux-en-Y gastric bypass in humans.

AIMS: Ghrelin is a gastric-derived hormone that stimulates growth hormone (GH) secretion and has a multi-faceted role in the regulation of energy homeostasis, including glucose metabolism. Circulating ghrelin concentrations are modulated in response to nutritional status, but responses to ghrelin in altered metabolic states are poorly understood. We investigated the metabolic effects of ghrelin in obesity and early after Roux-en-Y gastric bypass (RYGB). MATERIALS AND METHODS: We assessed central and peripheral metabolic responses to acyl ghrelin infusion (1 pmol kg-1 min-1 ) in healthy, lean subjects (n = 9) and non-diabetic, obese subjects (n = 9) before and 2 weeks after RYGB. Central responses were assessed by GH and pancreatic polypeptide (surrogate for vagal activity) secretion. Peripheral responses were assessed by hepatic and skeletal muscle insulin sensitivity during a hyperinsulinaemic-euglycaemic clamp. RESULTS: Ghrelin-stimulated GH secretion was attenuated in obese subjects, but was restored by RYGB to a response similar to that of lean subjects. The heightened pancreatic polypeptide response to ghrelin infusion in the obese was attenuated after RYGB. Hepatic glucose production and hepatic insulin sensitivity were not altered by ghrelin infusion in RYGB subjects. Skeletal muscle insulin sensitivity was impaired to a similar degree in lean, obese and post-RYGB individuals in response to ghrelin infusion. CONCLUSIONS: These data suggest that obesity is characterized by abnormal central, but not peripheral, responsiveness to ghrelin that can be restored early after RYGB before significant weight loss. Further work is necessary to fully elucidate the role of ghrelin in the metabolic changes that occur in obesity and following RYGB.

Early weight regain after gastric bypass does not affect insulin sensitivity but is associated with elevated ghrelin.

OBJECTIVES: We sought to determine: (1) if early weight regain between 1 and 2 years after Roux-en-Y gastric bypass (RYGB) is associated with worsened hepatic and peripheral insulin sensitivity, and (2) if preoperative levels of ghrelin and leptin are associated with early weight regain after RYGB. METHODS: Hepatic and peripheral insulin sensitivity and ghrelin and leptin plasma levels were assessed longitudinally in 45 subjects before RYGB and at 1 month, 6 months, 1 year, and 2 years postoperatively. Weight regain was defined as ≥5% increase in body weight between 1 and 2 years after RYGB. RESULTS: Weight regain occurred in 33% of subjects, with an average increase in body weight of 10 ± 5% (8.5 ± 3.3 kg). Weight regain was not associated with worsening of peripheral or hepatic insulin sensitivity. Subjects with weight regain after RYGB had higher preoperative and postoperative levels of ghrelin compared to those who maintained or lost weight during this time. Conversely, the trajectories of leptin levels corresponded with the trajectories of fat mass in both groups. CONCLUSIONS: Early weight regain after RYGB is not associated with a reversal of improvements in insulin sensitivity. Higher preoperative ghrelin levels might identify patients that are more susceptible to weight regain after RYGB.