EVALUATION OF HYPOTHALAMIC-PITUITARY-GONADAL (HPG) FUNCTION IN PATIENTS WITH TURNER SYNDROME (TS) WITH THE GnRH ANALOG (GnRHa) SUBACUTE TEST

Abstract

We have previously described that a GnRH test (100 ug of SC Buserelin acetate administered twice at a 24 hs interval) can be used to evaluate the HPG axis in normal prepubertal girls (J Pediat 122:46,1993). In order to evaluate ovarian steroidogenic capacity and the role of sex steroids (SS) in the regulation of pituitary gonadotropins LH and FSH at late prepuberty (Pre), a GnRHa test was carried on in 14 girls with TS and bone ages (BA) between 6.16 and 12 years (y). Serum LH, FSH and E2 was evaluated in basal (B) conditions. 24 hs after the first and 4, 6 and 24 hs after the second injection of Buserelin. A positive response of serum E2 (E2≥55 pmol/L) was only detected in 4 patients. To evaluate LH and FSH responses, patients were divided into 2 groups (Gr) as a function of E2 response: Gr1(E2 ≥55pmol/L), mean±SD chronological age (CA) 9.94±1.84 y and BA 7.41±1.33 y and Gr2 (E2 <55pmol/L, n=10), CA 11.5±3.34 y and BA 9.97±2.49 y. BA was similar in the two groups. B LH and FSH in Gr1 was significantly lower than in Gr2: Median(M) LH was 0.31 (r:0.15-0.49) and 6.79 (r:0.1-54.1) while M FSH was 12.5(r:8.07-17.5) and 43.8(r:8.81-135) U/L, respectively, p<0.05 Dunn's test. Serum LH response to GnRHa was significantly different between Gr1 and Gr2 only 24 hs after the second stimulation (median 1.09, r:0.31-6.6 and 5.1, r:1.21-58, respectively, p<0.05). FSH was similar in the two groups at every sampling time. Conclusions: 1) the GnRHa test in TS is useful to evaluate the steroidogenic capacity of the ovary, 2) lack of difference in FSH response to GnRHa in the two groups would suggest similar ovarian inhibin deficiency, and 3) the differences between Gr1 and Gr2 in B LH and in LH 24 hs after the second GnRHa stimulation suggest that ovarian SS play a role in the regulation of LH secretion in late prepuberty as well as in early puberty.