EVALUATION OF CORTISOL SECRETION WITH THE INSULIN TOLERANCE TEST IN SHORT NORMAL CHILDREN

Abstract

The insulin tolerance test (ITT) is a classic method to assess the secretion of growth hormone (GH) and Cortisol. The objective of this study was to determine the dynamics of Cortisol secretion after hypoglycemia in 31 normal children (F=9, M=22) with short stature, normal growth velocity and normal GH response to ITT and/or clonidine. Mean chronological age was 12.4 ± 2.7 years. Glucose, Cortisol and GH during ITT (0.1 lU/kg i.v.) were measured at - 20, 0, 30, 60 and 90 minutes. All the patients developed significant hypoglycemia with a decrease in blood glucose from 79.8 ± 8.9 to 34.1 ± 9.8 mg/dl. We found a significant inverse correlation between basal Cortisol and peak increment of Cortisol, (r=-0.79, p<0.0001). Patients were divided into two groups according to the level of basal normal Cortisol for age and sex. Group A (n=13): basal Cortisol levels within the normal range; Group B (n=18): basal Cortisol above 2 SD from the normal mean levels. In group A we found a significant increment in Cortisol during the ITT (ANOVA, p<0.0001), while group B did not show a significant increment in Cortisol during the test in spite of having similar hypoglycemia as Group A (ANOVA). There were no differences in peak GH during the test between the groups.In summary, we found that the basal level of Cortisol influences significantly its increment during ITT, the greater the basal levels, the lower the increment. We believe that this finding, as well as the documentation of the degree of hypoglycemia, is important to interpret the results of an insulin tolerance test.