Growth hormone suppression and glutamine flux associated with cardiac surgery

Pharmacological doses of growth hormone (GH) in humans and rats increase plasma and muscle glutamine values. As major surgery results in a physiological rise in serum GH concentration, we investigated whether this physiological increase in GH altered glutamine metabolism. Eighteen patients undergoing coronary artery bypass graft (CABG) surgery were randomly assigned to receive somatostatin, 100 micrograms subcutaneously at induction of anaesthesia and 8 hourly for 48 h, or placebo. Somatostatin effectively blocked the physiological surge of GH following injury but did not affect plasma or muscle glutamine concentrations, which fell significantly in both groups. Plasma glutamine decreased by 31% (P < 0.01) and 28% (P < 0.01) in the control and somatostatin groups respectively. Muscle glutamine was reduced 45% (P < 0.001) in the control group and 50% (P < 0.001) in the somatostatin group. There was no difference in muscle or circulating glutamate, alanine or branched chain amino acid concentrations or in metabolite values between the somatostatin-treated patients and the control group. There was no relationship between the GH response to surgery and glutamine metabolism following major surgery.