IMPAIRED RESPONSE OF GHRH MEASURED IN PLASMA AFTER LDOPA STIMULATION IN PATIENTS WITH IDIOPATHIC DELAYED PUBERTY: NORMALISATION WITH START OF PUBERTY

Abstract

In order to investigate the regulation of GH secretion in patients with idiopathic delayed puberty (IDP) either prepubertal (stage PI) or early pubertal (P2) GHRH levels in plasma were measured after stimulation with L-Dopa in a group of 16 patients with IDP. The results were compared to those obtained in 12 patients with constitutional short stature (CSS) at the same stage of puberty who underwent L-Dopa test for insufficient height. Plasma GHRH levels were measured after extraction by RIA. After L-Dopa intake the peak of GH was mean ± SEM 8.6 ± 1.4 ng/ml in IDP and 12.0 ± 0.8 ng/ml in CSS (NS). The peak of GHRH after L-Dopa was 41 ± 10 pg/ml in IDP and 96 ± 25 pg/ml in CSS (p<0.02). Basal plasma GHRH levels were measured in five patients with IDP before and after 3 × 1500 IU of hCG. Testosterone levels rose to 4.8 ± 0.9 ng/ml, no changes in plasma GHRH levels were observed (25 ± 13 pg/ml). Oxandrolone was given in 6 patients with IDP. Six months after when puberty was clearly started with an increase in growth velocity (6.3 ± 0.7 cm/6 months) peak GHRH levels during L-Dopa stimulation test increased significantly (p<0.02) from 48 ± 12 pg/ml to 142 ± 33 pg/ml, GH peaks being respectively 8.4 ± 3.2 pg/ml before, 11.4 ± 1.9 after. These results suggest an hypothalamic dysfunction in patient with IDP, reversible with the start of puberty. They indicate a relationship between the wellknown partial and transitory GH deficiency found in some adolescents having a pubertal delay and their secretion of GHRH.