Urinary GH and IGF-I excretion in nine year-old children: relation to sex,current size and size at birth

OBJECTIVES To study the relationship of 24-hour urinary growth hormone (GH) and IGF-I excretion in childhood to sex and body size. To test the hypothe sis that small size at birth followed by postnatal catch-up growth is assoc iated with elevated IGF-I production. DESIGN AND SUBJECTS Follow-up study of a cohort of 183 healthy children bor n in Salisbury, UK. MEASUREMENTS Weight and height, 24-h urinary growth hormone (uGH) and IGF-I (uIGF-I) excretion, and systolic and diastolic blood pressures. RESULTS At 9 years of age, 24-h uIGF-I excretion, but not uGH excretion, was strongly related to current weight (P<0.001) and height (P<0.001). Urinary GH and I GF-I excretion were positively correlated (r = 0.15, P=0.05). Boys excreted more uIGF-I per unit UGH than girls (uIGF-l/uGH molar ratio 32.1 compared to 21.0; P for difference = 0.002). There were no significant relationships of UGH, ulGF-I or uIGF-l/uGH molar ratio with birthweight, birthlength or head circumference at birth, nor with blood pressure at 9 years. 'Catch-up' growth, indicated by an increase in height SD scores between birth and 9 y ears, was associated with higher IGF-I excretion (P=0.01) and occurred in c hildren with taller parents (P<0.001). CONCLUSIONS Boys appear to be more sensitive to GH than girls, generating m ore uIGF-I in relation to uGH, Urinary IGF-I excretion at 9 years is relate d to both absolute height and to the degree of catch-up in height from birt h, Our results suggest that IGF-I production is strongly influenced by gene tic factors, but also by either the degree to which intrauterine growth fal ls short of genetic growth potential, or the process of postnatal catch-up growth that follows.