Ethanol feeding impairs insulin-stimulated glucose uptake in isolated rat skeletal muscle: role of Gs alpha and cAMP.
BACKGROUND
The mechanism by which chronic alcohol consumption impairs insulin sensitivity is unclear. We investigated the role of the Gs alpha-mediated pathway in decreasing insulin sensitivity in skeletal muscle after ethanol consumption.


METHODS
Sixty male Wistar rats, divided into four groups, received either distilled water (controls; group I) or ethanol, which was administered by a gastric tube as a single daily dose of 5 g/kg (group II), 2.5 g/kg (group III), or 0.5 g/kg (group IV). After 20 weeks, fasting plasma glucose and serum insulin levels were measured. The hyperinsulinemic-euglycemic clamp study was performed under anesthesia to estimate whole-body insulin sensitivity. Insulin-stimulated glucose uptake was measured in vitro in dissected gastrocnemius muscle. Expression of glut4, Gs alpha, and Gi alpha was quantified using real-time PCR analysis and western blotting. cAMP levels were measured by ELISA.


RESULTS
Compared with controls, the following observations were made: (1) the hyperinsulinemic-euglycemic clamp study revealed impaired insulin action at the whole-body level after ethanol treatment; (2) chronic ethanol feeding at 5 g/kg and 2.5 g/kg significantly decreased both basal and insulin-stimulated glucose uptakes in isolated skeletal muscle (p<0.05), which was accompanied by decreased expression of glut4 (p<0.05); (3) Gs alpha (mRNA and protein) expression in skeletal muscle was significantly increased in all three ethanol groups (p<0.05), and cAMP levels were also increased by ethanol treatment (p<0.05); and (4) there was no significant change in Gi alpha expression in all three ethanol groups.


CONCLUSIONS
Chronic ethanol exposure decreased insulin-induced glucose uptake in rat skeletal muscle, which was associated with increased expression of Gs alpha. Because Gs alpha is a negative regulator of insulin sensitivity, the alteration in Gs alpha expression may contribute to the ethanol-induced impairment of insulin signal transduction.
Wan
Qiang
Q
Shandong Provincial Hospital, Shandong University, Jinan, China.
Liu
Yi
Y
Guan
Qingbo
Q
Gao
Ling
L
Lee
Kok Onn
KO
Zhao
Jiajun
J
D000428:Alcohol Drinking / Q000009:adverse effects* / Q000235:genetics / Q000503:physiopathology; D000437:Alcoholism / Q000235:genetics / Q000503:physiopathology*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D000431:Ethanol / Q000633:toxicity*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics / Q000502:physiology*; D051275:Glucose Transporter Type 4 / Q000235:genetics; D007328:Insulin / Q000502:physiology*; D007333:Insulin Resistance / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000503:physiopathology; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar
D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D007328:Insulin; D012333:RNA, Messenger; D000431:Ethanol; D000242:Cyclic AMP; D019205:GTP-Binding Protein alpha Subunits, Gs