Insulin-like growth factor-I blood levels in severely burned patients: effects of time post injury, age of patient and severity of burn.

Abstract

Insulin-like growth factor-I (IGF-I) is a polypeptide growth factor that stimulates protein synthesis. The aims of this study were to determine (1) the effect of a severe burn on blood IGF-I levels and (2) the variables controlling IGF-I level variations during recovery of these hypermetabolic patients. Eleven patients, nine men and two women (age range 22-55 years) were studied for 25 days following a severe burn (18-75% of total body surface area, mean 36%). Nitrogen balances were recorded daily and total IGF-I levels were measured every 3 days. IGF-I was extracted from serum using a validated formic acid-acetone methodology, then measured by a double antibody radioimmunoassay. IGF-I levels were compared to those of a reference healthy population. Within 24 hours following injury, IGF-I levels were low in all patients when compared to normal values for the same age range (mean +/- SEM of all patients, 131 +/- 26 micrograms/l). They remained low for the first week (days 4 and 7, 109 +/- 16 micrograms/l), then increased to reach normal values at the end of the study period (days 10-16, 144 +/- 19 micrograms/l, P = 0.005 when compared to days 4-7; days 19-25, 206 +/- 30 micrograms/l, P = 0.008 when compared to days 10-16). IGF-I levels were negatively correlated with age in the second phase of recovery only (days 10-16, r = -0.70, P < 0.05; days 19-25, r = -0.75, P < 0.01) and with severity of burn between days 19 and 25 (r = -0.62, P < 0.05). The presence of bronchial burn injury tended to lower IGF-I blood concentration (P = 0.08). Whereas IGF-I concentrations increased in the later phase of recovery, nitrogen balances did not. As a result, there was no significant correlation between these parameters. IGF-I levels followed a biphasic pattern in severely burned patients. They dropped dramatically in response to the traumatic shock, then increased during recovery. The degree of increase was dependent on the age of the patient and on the severity of the burn, but was not associated with an improvement in the nitrogen balance.