Immunoreactive Somatomedin C/Insulin-Like Growth Factor I in Urine from Normal Subjects, Pituitary Dwarfs, and Acromegalics

ABSTRACT: Using antibodies to somatomedin C/insulin-like growth factor I (SmC) produced in rabbits using the recombinant hormone, we have developed a radioimmuno-assay for SmC. Gel-chromatography of urine revealed that the vast majority of immunoreactive SmC was eluted coincident with 125I-SmC and a small portion eluted with fractions having a mol. wt. range of 30,000–40,000. The SmC concentration in urine was determined by radioimmuno-assay after ammonium sulfate extraction. Values did not ordinarily exceed 1 ng/ml. When the values from normal subjects were expressed as ng/mg creatinine, high levels were observed in the neonatal period. These values fell rapidly in infancy, declined more gradually in childhood, were slightly elevated at early puberty, and were lowest in adulthood. Urine SmC concentrations in 15 pituitary dwarfs were lower than the averages obtained from age-matched control subjects, and six of them showed abnormally low values. Three patients with active acromegaly had high SmC values in urine. In conclusion, 1) SmC, mainly of monomeric form, was immunologically detected in urine. 2) Radioimmunoassay for urine SmC revealed that values varied considerably with age in normal subjects and were partially dependent on the human growth hormone status. However, the full meaning of the findings remains to be elucidated.

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