Effects of Glucocorticoid-Treatment and/or Adrenalectomy on the Changes of Plasma Glucose and NEFA Levels after Insulin Injection in Sheep

Abstract

To investigate roles of glucocorticoids in insulin tolerance in ruminants, this study was carried out using the intact and glucocorticoid-treated and/or adrenalectomized (ADX) sheep. Experiment 1: Ascending graded doses of insulin (0.05, 0.1, 0.2 and 0.4IU/kgBW) were injected intravenously into two ADX sheep weekly to determine the dosage of insulin necessary to induce hypoglycemic signs. Experiment 2: Five treatments were involved in Experiment 2. Saline and insulin were injected intravenously in Treatment 1 and 2, respectively. The sheep in both treatments were intact. In Treatment 3, insulin was injected into the ADX animals. In Treatment 4 and 5, insulin was injected into the ADX animals after preglucocorticoid-treatment (25mg/head/day and 50mg/head/day, respectively, for three consecutive days). The insulin dosage was always 0.4IU/kgBW. The changes of plasma glucose and non-esterified fatty acid (NEFA) levels were then surveyed. In Experiment 1, one animal showed hypoglycemic signs at 0.1IU/kgBW of insulin and the other at 0.4IU/kgBW. In Experiment 2, all animals in Treatment 3 showed hypoglycemic signs. In Treatment 2, 4 and 5, no animal showed any hypoglycemic signs, though the plasma glucose level decreased to nearly 20mg/dl. On the other hand, the plasma NEFA level in Treatment 2 rapidly increased to about 900μeq/l within two hours after the insulin injection and the maximum level was nine times as high as the initial level. In Treatment 3, however, the plasma NEFA level did not remarkably increase. Though no hypoglycemic signs appeared in Treatment 4 and 5, the plasma NEFA levels were still about 500μeq/l, which were not significantly different from that in Treatment 3. In this study, it was confirmed in sheep that the insulin tolerance which had been lost by adrenalectomy was restored by preglucocorticoid-treatment. From these facts, it is suggested that glucocorticoid plays an important role in the underlying mechanism in ruminant insulin tolerance.