Aims/hypothesis: Ceramide is the main second messenger in the sphingomyelin-transmembrane signalling pathway. The compound is likely to play a role in the induction of insulin resistance. The aim of the present study was to examine the effect of streptozotocin diabetes on the content and composition of ceramides and sphingomyelins and the activity of neutral Mg (2+)-dependent sphingomyelinase and acid sphingomyelinase in different types of skeletal muscle of the rat.
Methods: The experiments were carried out on two groups of male Wistar rats weighing 250-280 g: controls and those treated with streptozotocin at a dose of 60 mg/kg. Determinations were performed on three types of skeletal muscle: the slow-twitch oxidative (soleus), fast-twitch oxidative-glycolytic (red section of the gastrocnemius) and fast-twitch glycolytic (white section of the same muscle). The content and composition of ceramide- and sphingomyelin-fatty acids were determined using gas-liquid chromatography. The activity of the enzymes was measured using N-[(14)CH (3)]-sphingomyelin as the substrate.
Results: Twelve different ceramides and sphingomyelins were identified and quantified in each muscle with regard to the fatty acid residue. The ratio of total content of ceramide-saturated fatty acids to the total content of ceramide-unsaturated fatty acids was more than two. In the case of sphingomyelin, the ratio was similar to ceramide in the soleus and much higher in both sections of the gastrocnemius. Treatment with streptozotocin increased the total content of ceramide-fatty acids by 78% (p < 0.001) in the soleus, 27.5% (p < 0.01) in the red and 36.9% (p < 0.001) in the white section of the gastrocnemius. Concomitantly, the total content of sphingomyelin-fatty acids decreased by 43.8%, 31.2%, 24.8% (p < 0.001 in each case) in the respective muscles. The activity of neutral Mg (2+)-dependent sphingomyelinase was elevated by 69.5%, 105.9% and 62.3% in the soleus and red and white gastrocnemius, respectively (p < 0.001 for each muscle). The activity of acid sphingomyelinase was stable in the soleus and white gastrocnemius and decreased by 15.7% (p < 0.01) in the red gastrocnemius.
Conclusion/interpretation: The results obtained show that insulin deficiency results in elevation in the content of ceramide in skeletal muscles. This indicates that the hormone is involved in regulation of the activity of the sphingomyelin-signalling pathway in the muscles.