Effects of acute heat stress on lipid metabolism of bovine primary adipocytes

Heat stress (HS) affects numerous physiological processes including nutrient partitioning and lipid metabolism. Objectives of this study were to evaluate how acute HS affects lipid metabolism in subcutaneous adipose tissue of dairy cattle. Adipose tissue biopsies were performed on Holstein cows for bovine primary adipocyte isolation and cultured at either 42 degrees C (HS) or 37 degrees C (thermal neutral, TN). Adipocytes were incubated with increasing isoproterenol (ISO), and with increasing concentrations of insulin in the presence of ISO to evaluate changes in lipolysis. Incorporation of radioactive acetate into lipids was measured as an indicator of lipogenesis. Abundance and phosphorylation of several lipolytic and lipogenic proteins were also measured. Adipocytes exposed to HS had an elevated maximal response to ISO and were more sensitive to lipolytic stimulation by ISO compared with cells cultured at TN. Thermal treatment did not affect the antilipolytic effects of insulin in the presence of ISO. Lipogenesis measured as acetate incorporation was not altered by HS, but a temperature by insulin interaction was observed for the regulation of acetyl CoA carboxylase, such that the presence of insulin resulted in a reduction in phosphorylation of acetyl CoA carboxylase in adipocytes cultured at TN but not HS conditions. Results of this study demonstrate that acute HS has a direct effect on the regulation of lipolysis and the rate-limiting enzyme of lipogenesis in isolated bovine adipocytes.