Abstract
The number of insulin receptors in edible dormouse adipocyte changes during the annual cycle. Expressed per micrometer squared of cell area, high-affinity sites vary from 1.4 ± 0.4 in December to 4.4 ± 0.02 in June ( P < 0.001), and low-affinity sites from 6.6 ± 1.6 to 40 ± 4 ( P < 0.001). Despite this increase in the number of receptors, adipocyte insulin sensitivity is minimal during spring and summer. We have therefore tried to determine the causes of the dormouse adipocyte insensitivity to insulin with respect to glucose metabolism. In order to study seasonal variations in the relative activity of the pentose-phosphate pathway (PPP) and Embden-Meyerhof pathway (EMP), the appearance rate of C 1 and C 6 of the glucose molecule in CO 2 production by incubated adipose tissue was measured. Glucose-6-phosphate dehydrogenase (G6PDH) activity was also analyzed. In autumn and in winter, the PPP is significantly more important than in spring and summer, when glucose is metabolized via the EMP. These results suggest that, in the edible dormouse, the decreased adipocyte insulin sensitivity in spring and summer may have its origin in the decrease of PPP activity.
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