GROWTH-HORMONE RESPONSE AFTER ADMINISTRATION OF L-DOPA, CLONIDINE, AND GROWTH-HORMONE RELEASING HORMONE IN CHILDREN WITH DOWN-SYNDROME

We studied the response of growth hormone secretion after the administration of L-dopa, clonidine, and growth hormone releasing hormone in eight growth-retarded children with Down syndrome aged f to 6.5 years. After L-dopa administration, five children had low growth hormone secretion (M = 3.7 ng/ml, SD - 2.12 at 30 min) and three children had elevated growth hormone levels (> 30 ng/ml). After clonidine administration, six children had relatively low growth hormone levels (M = 3.15 ng/ml, SD - 2.53 at 60 min) and two children had high levels (3&3 ng/ml and 16.8 ng/ml, respectively). There was a better response after growth hormone releasing hormone administration; only one child had a growth hormone level of < 10 ng/ml. Most of the children had a modified response of growth hormone secretion subsequent to the various stimulation tests. All children, however were able to secrete some growth hormone (greater-than-or-equal-to 10 ng/ml) at kast during one of the stimulation tests. In comparison with peak growth hormone levels reported in normal children our cohort had significantly lower growth hormone levels only after clonidine administration. It is postulated that children with Down syndrome have both anatomical and biochemical hypothalamic derangements that may result in decreased growth hormone secretion and reduced linear growth In addition, other mechanisms that may be in part responsible for the observed growth retardation are discussed.