Pituitary reserve after repeated administrations of releasing hormones in young and in elderly men: Reproducibility on different days

Abstract

Combined testing of the pituitary gland by administration of GHRH, CRH, GnRH and TRH has been proposed for clinical studies, although some reports indicate that individual endocrine responses can be different when releasing hormones are used alone or in combination. Aims of this study were to evaluate: 1) the reproducibility of the combined test on different days; 2) the endocrine responses to the combined test applied twice at 3h and at 5h interval; 3) differences of endocrine responses in young and in elderly men. Six healthy young men (aged 25 to 35 yr) and 6 healthy elderly men (aged 65 to 75 yr) were evaluated: elderly men had lower testosterone, free T3, and somatomedin-c levels than young men, while 17 beta-estradiol and inhibin were not significantly different, all values being within normal laboratory limits. The 12 men were tested on day 1 with iv GHRH (50 micrograms) CRH (50 micrograms), GnRH (100 micrograms) and TRH (200 micrograms) at 08:00h and again at 11:00h; on day 8, the same men were tested at 08:00h and again at 13:00h. At 08:00h, the endocrine responses were similar on day 1 and on day 8. The second GH (young and elderly men) and PRL (only young men) response was blunted on day 1, when the interval between two consecutive stimuli was 3h, but not on day 8, when the interval was 5h. Elderly men differed from young men only for GH and for PRL release on day 1 at 08:00h.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrasts in the gonadotropin-releasing hormone dose–response relationships for luteinizing hormone, follicle-stimulating hormone and α-subunit release in young versus older men: appraisal with high-specificity immunoradiometric assay and deconvolution analysis

“…In addition, because the dosing sequence of GnRH injections might influence individual glycoprotein hormone secretory responses, we randomized the order of GnRH doses and gave the highest (100//g) GnRH dose last. In this regard, a recent study using four different releasing hormones showed some time-dependent blunting of LH and FSH release when repeated fixed doses of 100 µg of GnRH were given iv (21), but gonadotropin levels in young and older men did not differ. Importantly, our randomized GnRH dose-response curve showed no evidence of an order effect or of progressively reduced LH, FSH or a-subunit release at the three highest doses of GnRH tested here.…”