Relative adrenal insufficiency. Does it exist in critically ill horses?

The adrenal insufficiency is a rare disease in horses. Hypoadrenocorticism is may be primary due to failure of glucocorticoid production from adrenocortical dysfunction, or secondary from failure of ACTH production due to pituitary dysfunction. RAI is reported in septic neonatal or prematuraly induced foals. Adrenal gland function is assessed by performing an ACTH stimulation test, in which exogenous ACTH is administered. The test can lead to a false diagnosis in the case of RAI. The author performed a study to determine the lowest dosage of ACTH required to produce a significant increase in cortisol concentration. An ACTH stimulation test was performed every 3 days on 5 occasions for each of 8 horses. Four dosages of cosyntropin were tested with cortisol concentration, measured using radioimmunoassay. The lowest dose, where significant response was observed in all horses was 0.1 mu g/kg.