ENDOCRINE CHANGES IN CEREBROSPINAL-FLUID, PITUITARY EFFLUENT, AND PERIPHERAL PLASMA OF ANESTHETIZED PONIES

Objective-To investigate the effects of inhalation and total IV anesth esia on pituitary-adrenal activity in ponies. Animals-9 healthy ponies : 5 geldings and 4 mares. Procedure-Catheters were placed in the caver nous sinus below the pituitary gland and in the subarachnoid space via the lumbosacral space. After 72 hours, administration of acepromazine was followed by induction of anesthesia with thiopentone and maintena nce with halothane (halothane protocol), or for the IV protocol, anest hesia induction with detomidine and ketamine was followed by maintenan ce with IV infusion of a detomidine-ketamine-guaifenesin combination. Arterial blood pressure and gas tensions were measured throughout anes thesia. Peptide and catecholamine concentrations were measured in pitu itary effluent, peripheral plasma, and CSF. Peripheral plasma cortisol , glucose, and lactate concentrations also were measured. Results-intr avenous anesthesia caused less cardiorespiratory depression than did h alothane; ACTH, metenkephalin, arginine vasopressin, and norepinephrin e pituitary effluent and peripheral plasma concentrations were higher during halothane anesthesia, with little change during intravenous ane sthesia. Pituitary effluent plasma beta-endorphin and peripheral plasm a cortisol concentrations increased during halothane anesthesia only. Dynorphin concentrations did not change in either group. Hyperglycemia developed during intravenous anesthesia only. Minimal changes occurre d in CSF hormonal concentrations during anesthesia. Conclusion-The pit uitary gland has a major role in maintaining circulating peptides duri ng anesthesia. Compared with halothane, IV anesthesia appeared to supp ress pituitary secretion.