Tyrosine serum levels during anesthesia with high doses of fentanyl

Serum tyrosine levels were determined in two groups of women. First group included 30 healthy volunteers and the second group was formed by 83 patients submitted to gynecological surgery under anesthesia with fentanyl (0.05 mg/kg). The results showed that preoperative tyrosine levels were higher than control values and decreased under fentanyl anesthesia. Surgical stimulation did not modify tyrosine levels. When surgery was ended serum tyrosine levels reached control values. Under fentanyl-anesthesia a direct relationship between serum tyrosine levels, cardiovascular parameters and catecholamine changes as reported by other authors is suggested. We think tyrosine serum determination could be an indirect, easy and unexpensive measure of hormonal stress response.