title: Hypothalamic-pituitary-gonadal axis in two men with aromatase deficiency: evidence that circulating estrogens are required at the hypothalamic level for the integrity of gonadotropin negative feedback.
abstract: BACKGROUND
  In men, the feedback of gonadotropins is regulated by estrogens that come from the aromatization of testosterone, but the relative contribution to the inhibition of LH and FSH secretion by the amount of locally produced estrogens within the hypothalamus and/or the pituitary, and the amount of circulating estrogens still remains unknown.
  
  
  OBJECTIVE
  In order to evaluate the effect of regulation induced by estradiol on the hypothalamic-pituitary-gonadal (HPG) axis, we studied the pulsatility of LH and FSH in two aromatase-deficient men (called subject 1 and subject 2), in which the production rate of estrogen (both local and circulating) is completely, or at least severely, impaired.
  
  
  METHODS
  FSH and LH were evaluated in terms of their pulsated secretion and as GnRH-stimulated secretion in two phases: phase 1, before estrogen treatment; and phase 2, during estrogen treatment with 25 microg transdermal estradiol twice weekly.
  
  
  METHODS
  Blood samples were taken during phase 1 and phase 2 at 0800 h for basal measurements of LH, FSH, inhibin B, testosterone, and estradiol. The analysis of the pulsatility of LH and FSH was performed by sampling every 10 min for 8 h in the two phases. Gonadotropin response to GnRH-stimulation test was studied by serial standard sampling after 100 microg GnRH i.v. bolus in phases 1 and 2.
  
  
  RESULTS
  Estrogen treatment led to a significant reduction in both LH-pulsated frequency (7.5 +/- 0.7 in phase 1, 4.5 +/- 0.7 in phase 2) and amplitudes (3.5 +/- 0.006 in phase 1, 1.9 +/- 0.4 in phase 2) of peaks, whereas FSH showed only a conspicuous reduction in serum levels and a trend towards the reduction of the amplitudes of its peaks without modification of the frequency of the pulses. Both testosterone and gonadotropins decreased during phase 2, whereas estradiol reached the normal range in both subjects. Transdermal estradiol treatment significantly lowered the peaks of both serum LH and FSH after GnRH as well as the incremental area under the curve after GnRH administration in both subjects. Basal serum inhibin B levels were slightly higher before transdermal estradiol treatment (phase 1) than during estrogen treatment (phase 2) in both subjects.
  
  
  CONCLUSIONS
  The administration of estrogen to aromatase-deficient men discloses the effects of circulating estrogens on LH secretion, exerted both at pituitary level, as shown by the decrease of basal and GnRH-stimulated secretion of LH and the LH pulsed amplitude, and at hypothalamic level as shown by the reduction of the frequency of LH pulses. The present study, coupling the outcomes of basal, GnRH-stimulated and the pulsatile evaluation of LH and FSH secretion in two aromatase-deficient men, demonstrates that circulating estrogens play an inhibitory role in LH secretion by acting on the hypothalamus and the pituitary gland of men. The discrepancy among testosterone levels, the arrest of spermatogenesis and a slightly inappropriate respective increase of serum FSH (lower than expected) suggests a possible role of estrogens in the priming and the maturation of HPG axis in men, an event that has never occurred in these two subjects as a consequence of chronic estrogen deprivation.
authors.affiliation: Integrated Department of Medicine, Endocrinology, Metabolism and Geriatrics, University of Modena and Reggio Emilia, Modena, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Rochira
authors.forename: Lucia
authors.initials: L
authors.lastname: Zirilli
authors.forename: Alessandro D
authors.initials: AD
authors.lastname: Genazzani
authors.forename: Antonio
authors.initials: A
authors.lastname: Balestrieri
authors.forename: Claudio
authors.initials: C
authors.lastname: Aranda
authors.forename: Bibiana
authors.initials: B
authors.lastname: Fabre
authors.forename: Paula
authors.initials: P
authors.lastname: Antunez
authors.forename: Chiara
authors.initials: C
authors.lastname: Diazzi
authors.forename: Cesare
authors.initials: C
authors.lastname: Carani
authors.forename: Laura
authors.initials: L
authors.lastname: Maffei
mesh_terms: D000328:Adult; D001141:Aromatase / Q000172:deficiency*; D004967:Estrogens / Q000097:blood* / Q000502:physiology*; D025461:Feedback, Physiological; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism; D006062:Gonadotropins / Q000378:metabolism*; D006066:Gonads / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D011673:Pulsatile Flow; D012107:Research Design
chemical_list: D004967:Estrogens; D006062:Gonadotropins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D001141:Aromatase