Relative effects of estrogen, age, and visceral fat on pulsatile growth hormone secretion in healthy women

Am J Physiol Endocrinol Metab. 2009 Aug;297(2):E367-74. doi: 10.1152/ajpendo.00230.2009. Epub 2009 May 26.

Abstract

Growth hormone (GH) secretion is subject to complex regulation. How pre- and postmenopausal age (PRE, POST), estradiol (E(2)) availability, and abdominal visceral fat (AVF) jointly affect peptidyl-secretagogue drive of GH secretion is not known. To this end, healthy PRE (n = 20) and POST (n = 22) women underwent a low- vs. high-E(2) clamp before receiving a continuous intravenous infusion of GH-releasing hormone (GHRH) or GH-releasing peptide (GHRP-2). According to analysis of covariance, PRE and POST women achieved age-independent hypo- and euestrogenemia under respective low- and high-E(2) clamps. All four of age (P < 0.001), E(2) status (P = 0.006), secretagogue type (P < 0.001), and an age x peptide interaction (P = 0.014) controlled pulsatile GH secretion. Independently of E(2) status, POST women had lower GH responses to both GHRH (P = 0.028) and GHRP-2 (P < 0.001) than PRE women. Independently of age, GHRP-2 was more stimulatory than GHRH during low E(2) (P = 0.011) and high E(2) (P < 0.001). Stepwise forward-selection multivariate analysis revealed that computerized tomographic estimates of AVF explained 22% of the variability in GHRH action (P = 0.002), whereas age and E(2) together explained 60% of the variability in GHRP-2 drive (P < 0.001). These data establish that age, estrogen status, and AVF are triple covariates of continuous peptide-secretagogue drive of pulsatile GH secretion in women. Each factor must be controlled for to allow valid comparisons of GH-axis activity.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aging / drug effects
  • Aging / physiology*
  • Estradiol / administration & dosage
  • Estradiol / pharmacology*
  • Female
  • Gonadotropin-Releasing Hormone / agonists
  • Health
  • Human Growth Hormone / metabolism*
  • Humans
  • Intra-Abdominal Fat / drug effects
  • Intra-Abdominal Fat / physiology*
  • Leuprolide / administration & dosage
  • Middle Aged
  • Placebos
  • Pulsatile Flow / drug effects
  • Pulsatile Flow / physiology
  • Young Adult

Substances

  • Placebos
  • Human Growth Hormone
  • Gonadotropin-Releasing Hormone
  • Estradiol
  • Leuprolide