TDK conference 2015

Insulin plays a central role in the regulation of carbohydrate metabolism; therefore, altering the cellular processes of insulin production and signaling by feed additives has a great importance. Based on experiments conducted in mice, it has been already stated that orally applied butyrate has an impact on intestinal incretin hormone (GIP, GLP-1) production, stimulating insulin secretion, and on the insulin sensitivity as well. Previous studies of our Department have shown that butyrate also affects the production of incretins and insulin in chicken, although in a different manner compared to mouse. In the present study, comparative examinations were performed regarding the incretin and insulin secretion in rabbit; furthermore, it was also monitored how butyrate could influence the insulin sensitivity of various tissues in chicken.

Our trials were conducted with Pannon White rabbits and Ross 308 broiler chickens. In the phase of intensive growth, animals were treated with a daily sodium butyrate bolus (0.25 and 1.25 g/kg body weight, respectively) by a gastric tube. Prior to the first treatment and thereafter, blood samples were collected at given time points; then plasma insulin and incretin concentrations were measured. Tissue samples were taken from the liver, subcutaneous and abdominal adipose tissue and gastrocnemic muscle of chickens, to assess the expression of key proteins of insulin signaling by semiquantitative Western blotting.

Butyrate treatment of rabbits significantly increased the plasma concentration of GLP-1, whereas concentration of GIP was decreased. Expression of insulin receptor beta (IR beta) in the liver and adipose tissue of chickens was significantly decreased by butyrate treatment, however, increased in skeletal muscles. Expression of further proteins was influenced by butyrate mostly in the liver, where significant butyrate-associated decrease could be observed.

The obtained results in rabbit are partly differing from those of chicken, previously described by our research group, where plasma concentrations of both insulin and incretins were decreased by butyrate. The observed contradictions can be primarily explained with the differences between carbohydrate metabolism of mammals and birds. Expression of IR beta was increased by butyrate in the skeletal muscle of chicken, while it had a remarkable decreasing effect in the other examined organs, acting on glucose shifting and stimulating carbohydrate metabolism of skeletal muscles. In conclusion, it can be suggested that butyrate as a potent effector of incretin production and insulin signaling, may provide new possibilities in the modulation of insulin homeostasis.