In this regard, Houde et al. (2010) recently examined the liver sensitivity to rapamycin and reported that hepatic gluconeogenesis was enhanced by chronically inhibiting mTOR in rats. Chronic rapamycin administration also affected insulin-dependent OSI-744 signalling in skeletal muscles of diabetic Psammomys obesus, suggesting an impaired insulin sensitivity of these tissues in this animal model (Fraenkel et al., 2008). Based on these results, as well as on the fact that defective glucose metabolism in skeletal muscles is a major cause of impaired glucose homeostasis in type 2 diabetes, the aim of the present study was to investigate the effect of systemic and chronic administration in rats of the mTOR inhibitor rapamycin on glucose metabolism, in particular at the level of skeletal muscles.

To this end, euglycaemic hyperinsulinaemic clamps, the gold standard method to evaluate overall insulin sensitivity, were performed in association with the labelled 2-deoxy-glucose procedure to measure muscle insulin sensitivity. The mechanisms underlying the metabolic defects induced by rapamycin were further investigated in vitro using rat L6 myotubes. Finally, we determined the effect of rapamycin treatment in a rat model of high fat diet-induced obesity. Methods Reagents and antibodies All reagents and antibodies are described in Table S1. Animals Male Wistar rats (Charles River, Arbresle, France) were housed individually (23��C; light on: 07.00�C19.00 h) and allowed free access to water and diet (RM1; metabolized energy 2.61 kcal?g?1). Food intake and body weight were measured daily (09:00 h).

Rats were killed using isoflurane anaesthesia and rapid decapitation. Blood was collected, and tissues were freeze-clamped and stored at ?80��C for further analyses. All animal care and experimental procedures were in accordance with the Swiss guidelines for animal experimentation and were ethically approved by the Geneva health head office. Treatments An initial study was performed on rats fed a standard diet. In this experiment, 10 week-old animals (325 g �� 5 g) were randomly divided into three groups: an ad libitum fed control group; a Sirolimus-treated group and a pair-fed (PF) control group fed the same amount of food as that consumed by Sirolimus-treated rats. Sirolimus is a clinically formulated injectable form of rapamycin, which contains, in addition to rapamycin, other inactive components (0.1% Entinostat sodium CMC, 0.25% Polysobate 80) and was kindly provided by Wyeth Pharma GmbH (Munster, Germany). Animals received daily i.p. injections of either vehicle (0.1% sodium CMC, 0.25% Polysobate 80 in sterile water) for the control and the PF groups, or Sirolimus at a dose of 2 mg?kg?1?day?1. A second study was carried out on rats fed a high fat (HF) diet.