Nelson Vergel
Founder, ExcelMale.com
https://academic.oup.com/jcem/advan...jc.2018-00755/5055542?redirectedFrom=fulltext
Aromatized Estrogens Amplify Nocturnal Growth Hormone Secretion in Testosterone-replaced Older Hypogonadal Men
Context
Sex steroids regulate growth hormone (GH) secretion in men and women. Testosterone (T) increases GH secretion in older men with a relative lack of T, in hypogonadal men of all ages, and in patients undergoing gender reassignment. The role of estradiol (E2) in men less well defined.
Objective
The goal is to assess the contribution of aromatization of testosterone to spontaneous nocturnal and stimulated GH secretion.
Participants
Four groups of healthy older men (N = 74, age range 57-77 yr) were studied. The gonadotropic axis was clamped with the gonadotropin-releasing hormone antagonist, degarelix. Three groups received T and one group placebo addback. Two T-replaced groups were treated with anastrozole (an aromatase inhibitor) and either placebo or E2 addback.
Main outcome measures
Ten-min GH concentration profiles were quantified by deconvolution analysis, after (1) overnight sampling, and (2) (i) combined iv injection of GH-releasing hormone [GHRH] (0.3 µg/kg) and GH-releasing peptide-2 [GHRH-2] (0.3 µg/kg), and (ii) withdrawal of a 2-h somatostatin infusion (1 µg/kg/h).
Results
Estradiol add-back during aromatase inhibition increased basal (P=0.046), pulsatile (P=0.020) and total (P=0.018) GH secretion by 60-70%. E2 did not potentiate GH secretory stimuli. Logarithmically transformed pulsatile GH secretion correlated strongly and positively with concurrent E2 concentrations overall (P=0.028) and under anastrozole treatment (P = 0.005).
Conclusion
Estradiol administration in older men transdermally stimulates overnight pulsatile GH secretion. The exact site of E2 action cannot be ascertained from these experiments but may include hypothalamic loci involved in GH regulation, especially since GH secretagogue effects on somatotrope pituitary cells were not affected.
