PLASMA-GLUCOSE AND CORTISOL RESPONSES TO EXOGENOUS INSULIN IN FASTED DONKEYS

Susceptibility to equine hyperlipaemia is increased by poor food intak e. To assess the contribution of changes in insulin sensitivity, plasm a glucose and cortisol responses to an intravenous insulin challenge ( 0.4 Iu kg(-1) bodyweight) were compared with those observed after sali ne administration in six donkeys fasted either overnight or for three days. Three days of fasting decreased both the rate of insulin-induced hypoglycemia and the maximal hypoglycemic response. A transitory incr ease in plasma cortisol which peaked within one to four hours of insul in administration was observed in three of the six overnight-fasted do nkeys and in all of the three-day fasted donkeys; inter-animal variati on appeared to exist in the responsiveness of the hypothalamic-pituita ry-adrenocortical (HPA) axis to stimulation by insulin-induced hypogly cemia. Fasting is likely to present a risk of equine hyperlipaemia, at least in part, by the reduction in tissue sensitivity to the glucoreg ulatory action of insulin.