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The effect of intermittent tissue hypoxia on glucose tolerance and insulin sensitivity was investigated in normal rats. Intermittent hypoxia of 10% 0 2 atmosphere for three hours per day for three weeks led to increased serum insulin levels following an intravenous glucose load without any alteration of glucose tolerance (1 g glucose per kg body weight). These data do not support the hypothesis that the beneficial effect of physical training on glucose tolerance as demonstrated in normal and fatty ZUCKER rats is due to repeated phases of tissue hypoxia associated with the training procedure.

Isolated hindquarters of bilaterally nephrectomized and sham-operated rats were perfused in the presence and absence of ¹⁴C-labelled serine, respectively. After a perfusion period of 30 min ¹⁴C-serine was 4,074 ± 270 dpm/ml in the perfusion medium of sham-operated animals and decreased to 2,800 ± 190 dpm/ml in the medium of acutely uraemic rats. Muscle glycogen concentration in sham-operated animals was 1.10 ± 0.04 mg/g wet weight in the absence and 1.03 ± 0.11 mg/g in the presence of serine. In contrast, in acutely uraemic rats there was a glycogen concentration of 0.57 ± 0.09 mg/g in the absence of serine. Glycogen was increased in the presence of serine in the perfusion medium, the value being 1.50 ± 0.13 mg glycogen/g wet weight. Incorporation of labelled serine into skeletal muscle glycogen was significantly higher in acutely uraemic animals (15 ± 0.5 µmol/g glycogen) than in sham-operated animals (10 ± 0.4 µmol/g). The results are compatible with the hypothesis that serine increases muscle glycogen synthesis in acute uraemia.

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