therapy has been highly improved and has been tailored to have the best outcome in each woman.

Transcription

1 FERTILITY AND STERILITY VOL. 76, NO. 2, AUGUST 2001 Copyright 2001 American Society for Reproductive Medicine Published by Elsevier Science Inc. Printed on acid-free paper in U.S.A. Oral dehydroepiandrosterone supplementation modulates spontaneous and growth hormone-releasing hormoneinduced growth hormone and insulin-like growth factor-1 secretion in early and late postmenopausal women Alessandro D. Genazzani, M.D., Ph.D., a Massimo Stomati, M.D., b Claudia Strucchi, M.D., a Simone Puccetti, M.D., b Stefano Luisi, M.D., b and Andrea R. Genazzani, M.D. b University of Pisa, Pisa, Italy Received October 27, 2000; revised and accepted April 10, Reprint requests: Alessandro Genazzani, M.D., Ph.D., Clinica Ostetrica Gynecologica, Università di Modena, Via del Pozzo 71, Modena, Italy (FAX: ; algen@unimo.it). a Department of Obstetrics and Gynecology, University of Modena, Modena, Italy. b Department of Obstetrics and Gynecology, University of Pisa /01/$20.00 PII S (01) Objective: To evaluate the effects of dehydroepiandrosterone (DHEA) supplementation on the growth hormone-releasing hormone growth hormone (GHRH-GH) axis in lean and obese postmenopausal women. Design: Prospective study. Setting: Postmenopausal women in a clinical research environment. Patient(s): Thirty-one postmenopausal women were divided in two groups by age (50 to 55 and 60 to 65 years). Within each group, lean and obese patients were considered. Intervention(s): All patients underwent hormonal evaluations before and at the third and sixth month of therapy (50 mg of DHEA orally each day) and a GHRH test (1 g/kg) before and at the sixth month of treatment. Ultrasound and bone mass density (BMD) examinations were performed before and after the sixth month of therapy. Main Outcome Measure(s): Plasma dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), E 1,E 2, androstenedione (A), testosterone (T), osteocalcin, GH, insulin-like growth factor 1 (IGF-1) concentrations. Result(s): The levels of all of the steroids that derived from DHEA metabolism (E 1,E 2, A, T, DHEAS) and osteocalcin were increased in plasma under DHEA supplementation. The supplementation protocol also increased the levels of GH and IGF-1. However, GHRH-induced GH and IGF-1 responses were not modified by DHEA supplementation. Conclusion(s): Administration of DHEA significantly affects several endocrine parameters in early and late postmenopausal women independently from body mass index. Our data support the hypothesis that DHEA treatment acts similarly to estrogen-progestin replacement therapy on the GHRH-GH-IGF-1 axis. This suggests that DHEA is more than a more than a simple diet supplement or antiaging product ; rather it should be considered an effective hormonal replacement treatment. (Fertil Steril 2001;76: by American Society for Reproductive Medicine.) Key Words: DHEA, postmenopausal women, GH, IGF-1, GHRH test, weight, aging In men and in women aging is characterized byseveralendocrineandneuroendocrinephysiologic changes. Indeed, the hypoestrogenism related to the physiologic ovarian failure during the menopausal transition affects many organs and their relative functions (such as the urogenital, skin, cardiovascular, skeletal systems). To counteract the negative impact of such hypoestrogenic-induced changes, hormone replacement therapy has been highly improved and has been tailored to have the best outcome in each woman. At present, all possible formulations of estrogens, alone or in combination with progestins, have been applied to the postmenopausal hypoestrogenic condition. In the several years, 241

2 studies on aging have clearly demonstrated that a reduction in the patient s subjective feeling of well-being is not only strictly related to the hypoestrogenic milieu but also to the constant decrease of endogenous dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) production (1 5). Indeed, DHEA administration greatly improves several endocrine, metabolic, and psychologic parameters both in men and in women (6 8), although this has not been confirmed by all studies (9). Although DHEA supplementation is not considered a medical treatment, this steroid has specific effects on metabolic indexes (6, 9) and increases plasma androstenedione (A), testosterone (T), estradiol (E 2 ), and estrone (E 1 ) levels (3, 4, 6 9). Little attention has been focused on the growth hormone insulin-like growth factor 1 (GH-IGF-1) axis under DHEA supplementation and there is minimal knowledge on the possible effects of DHEA on somatotropes activity (7) and bone metabolism. Because DHEA administration must be considered a putative treatment for postmenopausal women, we evaluated the effects of chronic DHEA administration (50 mg daily) on endocrine and neuroendocrine parameters, such as the release of GH and IGF-1 as induced by growth hormonereleasing hormone (GHRH), in early and late postmenopausal women who were of normal or excess weight. The data presented here are part of a larger protocol study (10). MATERIALS AND METHODS Patients We selected 31 women (age range 50 to 65 years) from the outpatients who were being treated at the Department of Obstetrics and Gynecology, University of Pisa, Italy, for their postmenopausal condition. All of the patients gave their informed consent to participate to the study. The participants were healthy and none were being treated with any kind of replacement therapy for their postmenopausal condition. The exclusion criteria for the study were previous or current neoplasia; thromboembolism; liver, pancreatic, or renal diseases; and diabetes mellitus. None of the patients showed thyroid, adrenal, or PRL diseases and none of the participants were under treatment for cardiovascular disease or hypertension. All patients underwent ultrasound examination and a mammography before the study begin to exclude any kind of organic disease. The patients were divided in four groups according to their age and body mass index (BMI): Group A: 9 women, aged 50 to 55 years, BMI 20 to 24 Group B: 9 women, aged 50 to 55 years, BMI 25 to 30 Group C: 7 women, aged 60 to 65 years, BMI 20 to 24 Group D: 6 women, aged 60 to 65 years, BMI 25 to 30 Study Protocol The study protocol was approved by the local ethics committee of the University of Pisa, Pisa, Italy. All patients were given a daily oral dose of DHEA (50 mg; Rottapharm, Monza, Italy). Blood samples were obtained for each participant before and at the third and sixth months of treatment to determine the plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrone (E 1 ), progesterone (P), DHEA, DHEAS, testosterone (T), androstenedione (A), estradiol (E 2 ), osteocalcin, GH, and IGF-1. Before and at the sixth month of treatment, we evaluated the GHRHinduced GH and IGF-1 release by obtaining blood samples 15 minutes before and 15, 30, 45, 60, 75, 90, 105, and 120 minutes after a GHRH bolus (1 g/kg). All samples were immediately centrifuged and the plasma was stored at 20 C until assay. Assays All hormonal determinations were made during the same assay. Plasma DHEA, DHEAS, T, A, E 2, P, and GH concentrations were determined using commercially available radioimmune assay kits (Radim, Pomezia, Roma, Italy). The intra-assay and interassay coefficients of variation (%CV) ranged from 3.8% to 6.1% and from 6.4% to 8.5%, respectively. LH and FSH concentrations were determined using an immunofluorometric assay, as described elsewhere (11). Osteocalcin plasma concentrations were determined with the use of a commercially available ELISA kit (Radim, Pomezia, Roma, Italy) whose minimal detectable dose (MDT) was 0.5 ng/ml. Intra-assay and interassay coefficients of variation were 4.9% and 9.0%, respectively. Insulin-like growth factor-1 (IGF-1) concentrations were determined with the use of a radioimmune assay kit (Medgenix, Fleurus, Belgium) after acid-ethanol extraction had been performed as described by Daughaday et al. (12). Intra-assay and interassay coefficients of variation were 4.1% and 8.9%; the minimal detectable dose was 8.4 ng/ml (conversion factor to SI unit: ), as has been reported elsewhere (13). Statistical Analysis All of the data are expressed as mean SEM. The maximum GH or IGF response to GHRH stimulation was computed for each patient as the difference between the highest GH or IGF concentration observed after stimulation and time 0 concentration. The mean maximum value (mean maximum ) was computed for each group of patients and was also expressed as the percentage variation from time 0. The presence of a statistically significant difference between groups was tested, after analysis of variance (one-way ANOVA), with the use of Student s t-test for paired and unpaired data, as appropriate. 242 Genazzani et al. DHEA administration modulates the GHRH-GH-IGF-I axis Vol. 76, No. 2, August 2001

3 TABLE 1 Hormonal characteristics of patients under study. Patients LH miu/ml FSH miu/ml GH ng/ml DHEA ng/dl DHEAS g/ml Estradiol pg/ml Estrone pg/ml P ng/ml A ng/dl T ng/dl Osteocalcin ng/ml IGF-1 ng/ml Basal conditions Group A Group B d Group C a a a Group D a a a d a rd month of treatment Group A b b b b b b b b b b b Group B b b b b b b b b b b b Group C b b b b b b b b b a b Group D b b b b b b b b b b b 6th month of treatment Group A b b b b c b b b b b b Group B b b b b c b b b b b b Group C b b b b c b b b b a b Group D b b b b c b b b b b b Note: Part of these data are from a larger study (10). Mean SEM. a P.05 vs. Groups A and B. b P.05 vs. basal conditions. c P.01 vs. basal conditions. d P.05 vs. lean subjects (Groups A or C). Genazzani. DHEA administration modulates the GHRH-GH-IGF-I axis. Fertil Steril FERTILITY & STERILITY 243

4 FIGURE 1 Growth hormone response to the GHRH stimulation test in the four groups of women under study. (A), Lean postmenopausal women, aged 50 to 55 years. (B), Lean postmenopausal women, aged 60 to 65 years. (C), Overweight postmenopausal women, aged 50 to 55 years. (D), Overweight postmenopausal women, aged 60 to 65 years. Profiles of GH response appear relatively modified by the DHEA administration. Before treatment; ΠSixth month of treatment. Genazzani. DHEA administration modulates the GHRH-GH-IGF-J axis. Fertil Steril RESULTS The hormonal characteristics of the study participants are summarized in Table 1. Some differences among groups were observed. The oldest subjects (Groups C and D) showed lower basal DHEA, DHEAS, and A plasma levels than younger subjects (Group A and B), independent of body weight. Group C showed the lowest mean LH levels among the four groups. As expected, the LH and FSH levels decreased significantly and progressively throughout the 6 months of treatment in all four groups of patients whereas E 2 and E 1 levels increased. The DHEA treatment resulted in markedly higher E 1 concentrations in the oldest (lean and obese) postmenopausal patients, compared to the youngest. In addition, obese postmenopausal patients showed higher E 1 but not E 2 plasma levels compared to the patients of similar age, both before and under treatment. After 3 and 6 months of DHEA administration A, T, GH, IGF-1, and osteocalcin significantly increased in a parallel manner in all groups of patients with respect to baseline values. No changes where observed for P plasma levels (see Table 1). In all four groups of patients, the GHRH test evidenced a similar GH response before and under DHEA treatment (Fig. 1). The mean difference (mean ) in GH between the maximum response to the GHRH bolus and the levels at time 0 was similar in all groups of patients (Fig. 2A); as expected, when the mean was expressed as percentage of variation, it resulted significantly reduced after 6 months of treatment (see Fig. 2B). Such a reduction was due to the increased GH levels. The mean maximum GHRH-induced GH value before and after DHEA treatment was similar in all patients (see Fig. 2C), and only patients in Group D showed a significant increase (P.05) after 6 months of treatment. It has to be noted that, among all of the groups, the older obese patients (Group D) showed the lowest GH mean, the lowest GH percentage increase, and the lowest mean maximum GHRHinduced GH values (P.01). 244 Genazzani et al. DHEA administration modulates the GHRH-GH-IGF-I axis Vol. 76, No. 2, August 2001

5 FIGURE 2 GH response to GH-RH expressed as mean in Group A (lean postmenopausal women), Group B (obese postmenopausal women), Group C (lean, late postmenopausal women), and Group D (obese, late postmenopausal women). (A), Baseline. (B), Mean percent variation. (C), Mean maximum GH response. The different way of representing the response of GH might condition data interpretation even if it appears clear that aging and obesity induce a lower response of GH to GHRH (panels A to B). The dotted bar is before treatment; the stripped bar is the sixth month of treatment. **P.01 vs. all groups; *P.05 vs. before treatment In addition, the IGF-1 levels showed a statistically significant response to the GHRH bolus in all of the groups before and after administration of DHEA (Fig. 3). Interestingly, in Groups A, C, and D the IGF-1 mean difference (mean ) did not change after 6 months of DHEA administration; in Group B the showed a statistically significant difference (P.05) (Fig. 4A). The IGF-1 percentage of variation was significantly reduced in all groups after 6 months of treatment as well (see Fig. 4B). The mean maximum response of IGF-1 to GHRH stimulation was significantly higher after 6 months of treatment with respect to baseline values (see Fig. 4C). The mean bone mass density (BMD), measured via the lumbar spine and femur, did not show any statistically significant changes after 6 months of treatment among the four groups of study participants (data not shown). The ultrasound evaluation of endometrial thickness showed no statistically significant modifications throughout the 6 months of treatment ( mm before and mm after 6 month of treatment). DISCUSSION Genazzani. DHEA administration modulates the GHRH-GH-IGF-I axis. Fertil Steril The present study demonstrates that DHEA supplementation induces a statistically significant increase in the estrogenic and androgenic milieu and significantly affects the GH-IGF-1 axis in both early and late postmenopausal women. Aging women exhibit a significantly lowered DHEA and DHEAS production rate, which is related to the decreasing 17,20 desmolase enzymatic activity (14). Because this decrease minimally effects cortisol synthesis, the corticotropin-releasing factor (CRF) ACTH axis is minimally or not at all involved in the effect on DHEA levels (14 16). Our late postmenopausal patients had significant lower DHEA, DHEAS, and A plasma levels than the early postmenopausal women. In addition, the higher BMI seems to influence only estrone (E 1 ) plasma levels, as the obese patients showed a higher E 1 concentration than did the lean women, independent of age. Interestingly, obese late postmenopausal women had low LH levels; thus, the neuroendocrine control of GnRH-gonadotropins axis is probably significantly modified in aging women (17). The low LH levels might be also affected by the higher estrone plasma levels of these patients. Oral DHEA treatment annulled the differences observed between early and late postmenopause, including those strictly related to excess body weight. The only difference that persisted during the 6 months of treatment was low LH concentrations in the obese late postmenopausal women, which was a probably result of a specific effect of aging (17) and steroid-induced feedback. In contrast, plasma DHEA, DHEAS, A, T, E 2, and E 1 levels increased significantly throughout all 6 months of treatment. Plasma GH, FERTILITY & STERILITY 245

6 FIGURE 3 IGF-1 response to the GHRH stimulation test in the four groups of women under study. (A), Lean postmenopausal women, aged 50 to 55 years. (B), Lean postmenopausal women, aged 60 to 65 years. (C), Overweight postmenopausal women, aged 50 to 55 years. (D), Overweight postmenopausal women, aged 60 to 65 years. The profiles of IGF-1 response appear to be scarcely modified by the DHEA administration. Before treatment; Πsixth month of treatment. Genazzani. DHEA administration modulates the GHRH-GH-IGF-I axis. Fertil Steril IGF-1, and osteocalcin also increased significantly as a result of the positive modulation induced by DHEA and by its metabolites on both pituitary and peripheral tissues (i.e., bone). The positive modulation exerted by both estrogens and androgens on GH secretion mimics the effect that has already been observed for with both oral or transdermal estrogenic replacement therapy protocols (18 21). In fact, our data clearly show that not only did GH and IGF-1 significantly increase after DHEA administration, but they also responded to GHRH stimulation in a perfectly similar manner to what has been previously reported (16). In physiopathologic conditions that are different for age but similar for hypoestrogenic condition (i.e., secondary amenorrhea and postmenopause), the GHRH-induced GH response is not modulated by gonadal steroids at the pituitary level (13, 18, 22). As demonstrated by the unchanged GH level observed in all groups of patients, GHRH-induced GH release was not modified by the DHEA treatment (and by its related steroid milieu) even though GH basal plasma levels increased significantly in all groups. This observation supports the hypothesis that exogenous DHEA (and the steroid metabolites derived from its transformation) does not affect GH secretion. This is also supported by previous data showing that different doses of both transdermal estradiol (13, 22) or synthetic steroid (i.e., tibolone) (18) significantly modify the spontaneous GH pulsatile release but are not able to change the GHRHinduced GH response (13, 18, 22). An interesting observation was that obese late postmenopausal patients did not respond adequately to the GHRH bolus, as a result of their low endogenous DHEA, DHEAS, E 2, and E 1 levels. DHEA administration improved this condition. In fact, the mean maximum GH response to GHRH was significantly higher than before the treatment (even if lower than all other groups), supporting the hypothesis that the hyposteroidal milieu and the excess weight condition (i.e., overfeeding) negatively affect the GHRH-GH axis and that DHEA administration 246 Genazzani et al. DHEA administration modulates the GHRH-GH-IGF-I axis Vol. 76, No. 2, August 2001

7 FIGURE 4 IGF-1 response to GHRH expressed as (A), mean from baseline values, (B), mean percentage variation, or (C), mean maximum GH response in the early postmenopausal lean (Group A) and obese (Group B) and late postmenopausal lean (Group C) and obese (Group D) women. The different way of representing the response of IGF-1 might condition data interpretation. Only obese early postmenopausal women showed a significant IGF-1 (A). DHEA administration influenced IGF-1 response to GH-RH increasing IGF-1 plasma levels more than the entity of the response, because the IGF-1 response minimally changed (A B). Maximum IGF-1 responses were obviously increased (C). Dotted bar is before treatment; stripped bar is sixth month of treatment. *P.05 or **P.01 vs. before treatment. Genazzani. DHEA administration modulates the GHRH-GH-IGF-I axis. Fertil Steril induces an increase in GHRH-induced GH response from the somatotropes. The IGF-1 response to GHRH was also modified by DHEA administration. In fact, both the basal plasma levels and the mean maximal IGF-1 response to the GHRH bolus increased. The mean of IGF-1 level in obese early postmenopausal women was higher than in age-matched lean women, but this might be due to the higher estrone plasma levels present in baseline conditions. Such a difference was not observed in late postmenopausal patients, which suggests that aging might act on both liver activity/metabolism and its sensitivity to the estrogenic milieu. As a result of the DHEA treatment, all of the women showed a statistically significant increase in plasma osteocalcin levels, used as marker of bone remodeling and formation. This observation confirms the efficacy of DHEA administration not only at the central but also at the peripheral levels, acting on one of the systems (i.e., skeletal system) deeply affected by the postmenopausal hypoestrogenic milieu. According to our data, none of the patients showed a significant decrease in bone mass density during 6-month treatment. In consideration of the many steroids whose concentrations increased after DHEA administration, it is almost impossible to ascribe the effect on osteocalcin only to the androgenic or estrogenic milieu. Other modulators such as interleukin-6 (IL-6), the mediator of bone resorption in osteoporosis have been reported to decrease with DHEA supplementation (23). It can be argued that DHEA has a specific effect on all the modulators of bone remodeling, probably through its the metabolites (both androgens and estrogens). Our study demonstrates that exogenous DHEA administration significantly affects several endocrine parameters in early and late postmenopausal women, independent of the woman s weight. In addition, some of the differences that were considered to be related to excess weight or the aging process were reduced or annulled during DHEA administration. Our data support the hypothesis that DHEA treatment acts similarly to estrogen-progestin replacement therapy on GHRH-GH- IGF-1 axis. This suggests that DHEA is more than a simple diet integrator or antiaging product, but rather should be considered an effective hormone replacement treatment. References 1. Thomas G, Frenoy N, Legrain S, Sebag-Lanoe R, Baulieu EE, Debuire B. Serum dehydroepiandrosterone sulfate levels as an individual marker. J Clin Endocrinol Metab 1994;79: Baulieu EE. Dehydroepiandrosterone (DHEA): a fountain of youth? J Clin Endocrinol Metab 1996;81: Phillips GB. Relationship between serum dehydroepiandrosterone sulfate, androstenedione, and sex hormones in men and women. Eur J Endocrinol 1996;134: Guazzo EP, Kirkpatrick PJ, Goodhyer IM, Shiers HM, Herbert J. Cortisol, dehydroepiandrosterone (DHEA), and DHEA sulfate in the cerebrospinal fluid of man: relation to FERTILITY & STERILITY 247

8 blood levels and the effect of age. J Clin Endocrinol Metab 1996; 81: Lane MA, Ingram DK, Ball SS, Roth GS. Dehydroepiandrosterone sulfate: a biomarker of primate aging slowed by calorie restriction. J Clin Endocrinol Metab 1997;82: Mortola JF, Yen SSC. The effects or oral dehydroepiandrosterone on endocrine-metabolic parameters in postmenopausal women. J Clin Endocrinol Metab 1990;71: Morales AJ, Nolan JJ, Nelson JC, Yen SSC. Effects of replacement dose of dehydroepiandrosterone in men and women of advancing age. J Clin Endocrinol Metab 1994;78: Stomati M, Rubino S, Spinetti A, Parrini D, Luisi S, Casarosa E, et al. Endocrine, neuroendocrine and behavioural effects of oral dehydroepiandrosterone sulphate supplementation in postmenopausal women. Gynecol Endocrinol 1999;13: Flynn MA, Weaver-Osterholtz D, Sharpe-Timms KL, Allen S, Krause G. Dehydroepiandrosterone replacement in aging humans. J Clin Endocrinol Metab 1999;84: Stomati M, Monteleone P, Casarosa E, Quirici B, Pucetti S, Bernardi F, et al. Six-month oral dehydroepiandrosterone supplementation in early and late menopause: circulating steroids, gonadotropins sexhormone binding globulin, beta-endorphin and adrenal function. Gynecol Endocrinol, 2000;14: Genazzani AD, Petraglia F, Benatti R, Montanini V, Algeri I, Volpe A, Genazzani AR Luteinizing hormone (LH) secretory burst duration is independent from LH, prolactin, or gonadal steroid plasma levels in amenorrheic women. J Clin Endocrinol Metab 1991;72: Daughaday WH, Mariz IK, Blethen SL. Inhibition of access of bound somatomedin to membrane receptor and immunobinding sites a comparison of radioreceptor and radioimmunoassay of somatomedin in native and acid-ethanol extracted serum. J Clin Endocrinol Metab 1980;51: Genazzani AD, Gamba O, Petraglia F. Estrogen replacement therapy modulates spontaneous GH secretion but does not affect GH-RHinduced GH response and low T3 syndrome in women with hypothalamic amenorrhea associated to weight-loss. J Endocr Invest 1998;21: Liu CH, Laughlin GA, Fischer UG, Yen SSC. Marked attenuation of ultradian and circadian rhythms of dehydroepiandrosterone in postmenopausal women: evidence for a reduced 17,20 desmolase enzymatic activity. J Clin Endocrinol Metab 1990;71: Parker LN, Odell WD. Control of adrenal androgen secretion. Endocr Rev 1980;4: Yamaji T, Ibayashi H. Serum dehydroepiandrosterone sulphate in normal and pathological conditions. J Clin Endocrinol Metab 1969;29: Genazzani AD, Petraglia F, Sgarbi L, Montanini V, Hartmann B, Surico N, et al. Difference of LH and FSH secretory characteristics and degree of concordance between postmenopausal and aging women. Maturitas 1997;26: Genazzani AD, Gamba O, Nappi L, Volpe A, Petraglia F. Modulatory effects of a synthetic steroid (Tibolone) and estradiol on spontaneous and GH-RH-induced GH secretion in postmenopausal women. Maturitas 1997;28; Bellantoni MF, Harman SM, Cho DE, Blagman MR. Effects of progestin-opposed transdermal estrogen administration on growth hormone and insuline-like growth factor-i in postmenopausal women of different ages. J Clin Endocrinol Metab 1991;72: Bellantoni MF, Vittone J, Campfield AT, Bass KM, Harman SM, Blackman MR. Effects of oral versus transdermal estrogen on the growth hormone/insulin-like growth factor I axis in younger an older postmenopausal women: a clinical research center study. J Clin Endocrinol Metab 1996;81: Diamond P, Cusan L, Gomez JL, Belanger A, Labrie F. Metabolic effects of 12-month percutaneous dehydroepiandrosterone replacement therapy in postmenopausal women. J Endocrinol 1996; 150(suppl):S43 S Genazzani AD, Petraglia F, Volpogni C, Gastaldi M, Pianazzi F, Montanini V, Genazzani AR. Modulatory role of estrogens and progestins on growth hormone episodic release in women with hypothalamic amenorrhea. Fertil Steril 1993;60: Casson PR, Andersen RN, Herrod HG, Stentz FB, Straughn AB, Abraham GE, Buster JE. Oral dehydroepiandrosterone in physiologic doses modulates immune function in postmenopausal women. Am J Obstet Gynecol 1993;169: Genazzani et al. DHEA administration modulates the GHRH-GH-IGF-I axis Vol. 76, No. 2, August 2001