Growth hormone response to thyrotropin-releasing hormone in children and adolescents: a reappraisal

Abstract

ABSTRACT In normal subjects, thyrotropin-releasing hormone (TRH) is not involved in the control of growth hormone secretion. Paradoxical growth hormone (GH) responses to TRH have been described in acromegalic subjects and, recently, in some constitutionnally tall children. To confirm this finding, we have examined the GH response to combined LHRH-TRH tests performed to assess the pituitary function of children with GH deficiency, tall stature before and during bromocriptine therapy, precocious or delayed puberty as well as in a group of patients of average height and normal bone age. Unlike prolactin, the GH "response" to TRH, in children followed longitudinally, is particularly heterogeneous with an unpredictable pattern of secretion in repeated tests. Over 90% of children display peaks of GH (≥5ng/ml), of which 38% occur twice during the test period. Amplitude and frequency of GH peaks appear to be independent of height, chonological age or bromocriptine therapy. Secretory rate estimated by integrated surface area increases in parallel to sex steroids impregnation. The pattern of GH secretory episodes, the increase in mean GH secretion in parallel to the production of gonadal sex steroids and the failure of bromocriptine to affect GH secretion in constitutionnally tall children allow to speculate that what is measured after TRH injection is normal spontaneous GH rhythm rather than a direct effect of TRH on GH secretion.