A preoperative fasting plasma C-peptide level <1.0 nmol/l in severely obese T2DM patients indicates partial β-cell failure, and is associated with a markedly reduced chance of complete resolution of T2DM after RYGB. We therefore advocate measuring C-peptide levels in all diabetic patients up for bariatric surgery to improve the prediction of outcome.

The influence of thyroid hormone depletion and experimental hyperthyroidism on red and white skeletal muscle of the rat during periods of 2, 4 and 8 weeks were studied. Body weight, muscle weight, mitochondrial protein content, and specific activities of the mitochondrial enzymes \g=a\-glycerophosphatedehydrogenase (EC 1.1.99.5) (\g=a\-GPD) and succinate dehydrogenase (EC 1.3.99.1) (SDH) were used as parameters. The largest differences in body weight gain and muscle weight gain (both red and white muscle) in the hypothyroid rats were seen after 8 weeks of T4 treatment. In the hyperthyroid rats the weight of the red muscle and the ratio of the red muscle weight to the body weight increased, whereas the white muscle weight and the ratio of the white muscle weight to the body weight decreased relative to the control animals. In hypothyroid rats the mitochondrial protein content was lowered in both red and white muscle, the specific \g=a\-GPD activity only in the latter. No changes in specific SDH activity were observed in either type of muscle. The hyperthyroid rats showed an increase in the mitochondrial protein content and the specific \g=a\-GPDand SDH activity in the red muscle, whereas no significant changes were observed in the white muscle. The changes in the parameters under study show that the effect of the thyroid state differs in red and white muscle. An explanation for a possibly greater sensitivity of red than of white muscle to thyroid hormones is discussed.The object of this study was to investigate a possible difference between the susceptibility of red and white skeletal muscle of the rat to thyroid hormones. Evidence that thyroid hormones have a different action on red and white 768

T3 and T4 concentrations were determined in plasma and red and white skeletal muscle of the rat. Because of the small tissue samples (± 300 mg), the ultra-sensitive Wick radioimmunoassay (RIA) for serum was adapted for determination in ethanol extracts. The dilution curves of the plasma and tissue extracts showed excellent parallelism with the standard curves for both T3 and T4. The mean T4 level found in female rats (n = 6) was 22.6 ± 5.2 ng/ml in plasma and did not differ significantly between red (1.85 ± 0.28 ng/g) and white (1.90 ± 0.25 ng/g) skeletal muscle. The mean T3 level in 11 normal female rats was 0.629 ± 0.098 ng/ml in the plasma and was significantly higher in the red muscle (2.07 ± 0.26 ng/g) than in the white muscle (1.65 ± 0.20 ng/g). The higher T3 levels found in the red muscle as compared with the white muscle may help to elucidate the different responsiveness of these muscle types observed in altered thyroid states.

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