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The effects of high altitude on hypothalamic‐pituitary secretory dynamics in men
Author(s) -
Ramirez German,
Herrera Rafael,
Plneda David,
Blttle Polly A.,
Rabb Hamld A.,
Bercu Barry B.
Publication year - 1995
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1995.tb01887.x
Subject(s) - medicine , endocrinology , basal (medicine) , hormone , thyrotropin releasing hormone , endocrine system , pituitary gland , biology , insulin
Summary OBJECTIVE Individuals adapted to high altitude (HA) have abnormalities In endocrine function and specifically In the pituitary‐thyroid axis and aldosterone regulation. In this study we assessed hypothalamic‐pituitary function In men adapted to high altitude living using exogenous administration of synthetic hypothalamic hormones DESIGN Growth hormone releasing hormone (Geref 1‐29) 1 /μg/kg, TRH 500/μg, GHRH 100 μg and ovine cortlcotro‐phin releasing hormone (oCRH) 1 μg/kg were simultaneously administered Intravenously to two groups of men: 12 born and raised In the city of Pasto, Colombia, South America, located at an altitude of 2600 m In the southern Colombian Andes (HA group) and 10 men living at sea level (SL) in Tampa, Florida MEASUREMENTS The following hormones were measured: GH, IGF‐I, TSH, T4, free T4, free T3, PRL, ACTH, β ‐endorphln and Cortisol. IGF binding proteln‐3 (IGFBP‐3) and Cortisol binding globulin (CBG) were also measured. RESULTS G H response to G H R H In HA men was exaggerated compared to SL men, and I G F‐I concentration was also significantly Increased In the presence of normal levels of IGFBP‐3. No differences in T S H or P R L responses were found following TRH. HA men had lower basal total T4 levels, but higher free T4 and free T3 concentrations. The basal ACTH concentrations in the HA men were significantly lower than SL, although the response to oCRH was still present. β ‐Endorphln basal levels were similar at HA and SL but the response to oCRH at HA was blunted. At HA, basal Cortisol levels as well as C B G were elevated compared to SL and, In contrast to SL, did not increase significantly after endogenous ACTH secretion. CONCLUSIONS This study Is the first description of exaggerated G H response to the administration of G H R H In HA men and also of a significant increase in I G F‐I concentration in the same subjects in the presence of normal levels of IGFBP‐3. An altered hypothalamic‐pituitary response was found in HA men after administration of oCRH characterized by a significantly lower basal ACTH concentration at HA, although the response to oCRH was present but the β‐endorphin response to oCRH was blunted. At HA, basal Cortisol levels, as well as C B G, were elevated and the Cortisol levels did not significantly Increase after endogenous ACTH secretion. We have characterized the differences in hypothalamic‐pituitary dynamics after the administration of TRH, GnRH and oCRH In HA men comparing their response to age/ sex matched SL men