Maria Tereza Lombardi

Serum leptin concentration during puberty in healthy nonobese adolescents

Data obtained during the past five years have indicated that there are important age- and gender-based differences in the regulation and action of leptin in humans. To study the physiological changes of leptin during puberty in both sexes, and its relationship with body composition and sexual maturation, we measured leptin concentrations in 175 healthy adolescents (80 girls, 95 boys, 10-18 years of age), representing all pubertal stages. We excluded individuals with a body mass index (BMI) below the 5th or above the 95th percentile relative to age. Serum concentrations of leptin were determined by a monoclonal antibody-based immunofluorimetric assay, developed in our laboratory. Body composition was determined by dual-energy X-ray absorptiometry. Pubertal stage was assigned by physical examination, according to Tanner criteria for breast development in females and genital development in males. Leptin concentration in girls (N = 80) presented a positive linear correlation with age (r = 0.35, P = 0.0012), BMI (r = 0.65, P < 0.0001) and %fat mass (r = 0.76, P < 0.0001). In boys (N = 95) there was a positive correlation with BMI (r = 0.49, P < 0.0001) and %fat mass (r = 0.85, P < 0.0001), but a significant negative linear correlation with Tanner stage (r = -0.45, P < 0.0001) and age (r = -0.40, P < 0.0001). The regression equation revealed that %fat mass and BMI are the best parameters to be used to estimate leptin levels in both sexes. Thus, the normal reference ranges for circulating leptin during adolescence should be constructed according to BMI or %fat mass to assure a correct evaluation.

Desenvolvimento de ensaio imunofluorométrico para a medida da globulina ligadora de tiroxina (thyroxine-binding globulin, TBG) e sua aplicação em casos de deficiência desta proteína

Thyroxine-binding globulin (TBG) is the main responsible for serum thyroid hormone transport. Serum variations in TBG concentrations determine proportional variations in serum total T4 and T3 concentrations, without implications to function, since the free fraction remains normal. Several frequent clinical conditions lead to significant alterations in the TBG levels, being the most important variations due to genetic defects. Since TBG is codified by a gene localized in the X chromosome, the defects are more often found in males. We describe the development of an immunofluorometric assay for the measurement of TBG based on monoclonal antibodies, being one developed at our laboratories and the other obtained from commercial sources. The method presents sensitivity of 0.8mg/l and intra and inter-assay coefficients of variation of less than 10%. Comparison with a commercial assay showed high correlation (r = 0.93, n = 48), with normal values between 10mg/l and 29 mg/l. We also studied 20 individuals with congenital deficiency of TBG, 19 men and one woman, that presented normal TSH values and low total T4 values; in all of them the TBG values were undetectable. Free T4 values otherwise were high when measured with an indirect method in 16 of the individuals, and normal in the other four patients where they were measured with a direct post-dialysis method. Our results reinforce the practical need for an assay for the measurement of serum TBG for the diagnostic definition of some special cases, mainly when a direct free T4 assay is not available.