Hormonal blockade modifies post-traumatic protein catabolism

Abstract

Protein catabolism following injury is associated with elevated levels of the stress hormones cortisol, glucagon, and the catecholamines. To study the effect of hormonal blockade on catabolic responses to surgery, 16 dogs underwent general anesthesia, a standard abdominal operation, and implantation of aortic and caval catheters. Five received phentolamine and propranolol continuously, at doses which block catecholamine effects. To prevent the rise in both catecholamines and cortisol, 6 received a high epidural anesthetic (T4-S3), started preoperatively and continued for 24 hr. Five dogs served as controls. Hindquarter amino acid flux was measured at 6 and 24 hr post-op. Pre- and post-op skeletal muscle biopsies were analyzed for amino acids. Urinary nitrogen was measured over 24 hr. Urinary nitrogen excretion was unaffected by treatment, but urinary creatinine fell from 0.039 ± 0.002 g/24 hr · kg for controls to 0.03 ± 0.002 for the epidural group and 0.031 ± 0.001 for α and β blockade ( P < 0.05). Hindquarter amino acid nitrogen efflux was decreased from −19.05 ± 4.06 μmole/min · kg in controls to −8.98 ± 0.86 in the epidural and −6.89 ± 1.21 in the α- and β-blockade groups ( P < 0.05). The urinary nitrogen loss, glutamine efflux, and fall in muscle glutamine produced by the operation were not prevented by either form of hormonal blockade, but hindquarter nitrogen efflux was diminished. Hormonal blockade inhibits net skeletal muscle protein catabolism without altering whole-body nitrogen loss. Hormones and other factors must be responsible for the increased ureagenesis that occurs following injury.