Cholecalciferol ameliorates insulin signalling and insulin regulation of enzymes involved in glucose metabolism in the rat heart.

CONTEXT The evidence on potential cross-talk of vitamin D and insulin in the regulation of cardiac metabolism is very scanty. OBJECTIVE Cholecalciferol was administered to male Wistar rats for six weeks to study its effects on cardiac glucose metabolism regulation. MATERIALS AND METHODS An expression, phosphorylation and/or subcellular localisation of insulin signalling molecules, glucose transport and metabolism key proteins were studied. RESULTS Circulating non-esterified fatty acids (NEFA) level was lower after cholecalciferol administration. Cholecalciferol decreased cardiac insulin receptor substrate 1 Ser307 phosphorylation, while insulin-stimulated Akt Thr308 phosphorylation was increased. Cardiac 6-phosphofructo-2-kinase protein, hexokinase 2 mRNA level and insulin-stimulated glycogen synthase kinase 3β Ser9 phosphorylation were also increased. Finally, FOXO1 transcription factor cytosolic level was reduced. CONCLUSION Vitamin D-related improvement of insulin signalling and insulin regulation of glucose metabolism in the rat heart is accompanied by the decrease of blood NEFA level and dysregulation of cardiac FOXO1 signalling.