title: Multipathway modulation of exercise and glucose stress effects upon GH secretion in healthy men.
abstract: OBJECTIVE
  Exercise evokes pulsatile GH release followed by autonegative feedback, whereas glucose suppresses GH release followed by rebound-like GH release (feedforward escape). Here we test the hypothesis that age, sex steroids, insulin, body composition and physical power jointly determine these dynamic GH responses.
  
  
  METHODS
  This was a prospectively randomized glucose-blinded study conducted in the Mayo Center for Advancing Translational Sciences in healthy men ages 19-77 years (N=23). Three conditions, fasting/rest/saline, fasting/exercise/saline and fasting/rest/iv glucose infusions, were used to drive GH dynamics during 10-min blood sampling for 6h. Linear correlation analysis was applied to relate peak/nadir GH dynamics to age, sex steroids, insulin, CT-estimated abdominal fat and physical power (work per unit time).
  
  
  RESULTS
  Compared with the fasting/rest/saline (control) day, fasting/exercise/saline infusion evoked peak GH within 1h, followed by negative feedback 3-5h later. The dynamic GH excursion was strongly (R(2)=0.634) influenced by (i) insulin negatively (P=0.011), (ii) power positively (P=0.0008), and (iii) E2 positively (P=0.001). Dynamic glucose-modulated GH release was determined by insulin negatively (P=0.0039) and power positively (P=0.0034) (R(2)=0.454). Under rest/saline, power (P=0.031) and total abdominal fat (P=0.012) (R(2)=0.267) were the dominant correlates of GH excursions.
  
  
  CONCLUSIONS
  In healthy men, dynamic GH perturbations induced by exercise and glucose are strongly related to physical power, insulin, estradiol, and body composition, thus suggesting a network of regulatory pathways.
authors.affiliation: Endocrine Research Unit, Mayo Clinic College of Medicine, Center for Translational Science Activities. Electronic address: veldhuis.johannes@mayo.edu.
authors.forename: Johannes D
authors.initials: JD
authors.lastname: Veldhuis
authors.affiliation: Cardiovascular Research, Mayo Clinic, Rochester, MN 55905.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Olson
authors.affiliation: Primary Care Internal Medicine, Mayo Clinic, Rochester, MN 55905.
authors.forename: Paul Y
authors.initials: PY
authors.lastname: Takahashi
authors.affiliation: Endocrine Research Unit, Mayo Clinic College of Medicine, Center for Translational Science Activities.
authors.forename: John M
authors.initials: JM
authors.lastname: Miles
authors.affiliation: Anesthesia Research, Mayo Clinic, Rochester, MN 55905.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
authors.affiliation: Endocrine Research Unit, Mayo Clinic College of Medicine, Center for Translational Science Activities.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Yang
authors.affiliation: Endocrine Research Unit, Mayo Clinic College of Medicine, Center for Translational Science Activities.
authors.forename: Jean
authors.initials: J
authors.lastname: Wigham
mesh_terms: D050153:Abdominal Fat / Q000378:metabolism; D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism; D001823:Body Composition / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005215:Fasting / Q000378:metabolism; D025461:Feedback, Physiological; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D012739:Gonadal Steroid Hormones / Q000097:blood; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D012739:Gonadal Steroid Hormones; D007328:Insulin; D019382:Human Growth Hormone; D005947:Glucose
keywords: Age; Body composition; Metabolic; Somatotropin