Effects of high-altitude hypoxia on the hormonal response to hypothalamic factors

Abstract

Acute and chronic exposure to high altitude induces various physiological changes, including activation or inhibition of various hormonal systems. In response to activation processes, a desensitization of several pathways has been described, especially in the adrenergic system. In the present study, we aimed to assess whether the hypophyseal hormones are also subjected to a hypoxia-induced decrease in their response to hypothalamic factors. Basal levels of hormones and the responses of TSH, thyroid hormones, prolactin, sex hormones, and growth hormone to the injection of TRH, gonadotropin-releasing hormone, and growth hormone-releasing hormone (GHRH) were studied in eight men in normoxia and on prolonged exposure (3-4 days) to an altitude of 4,350 m. Thyroid hormones were elevated at altitude (+16 to +21%), while TSH levels were unchanged, and follicle-stimulating hormone and prolactin decreased, while leutinizing hormone was unchanged. Norepinephrine and cortisol levels were elevated, while no change was observed in levels of epinephrine, dopamine, growth hormone (GH), IGF-1, and IGFBP-3. The mean response to hypothalamic factors was similar in both altitudes for all studied hormones, although total T4 was lower in hypoxia during 45 to 60 min after injection. The effect of hypoxia on the hypophyseal response to hypothalamic factors was similar among subjects, except for the GH response to GHRH administration. We conclude that prolonged exposure to high-altitude hypoxia induces contrasted changes in hormonal levels, but the hypophyseal response to hypothalamic factors does not appear to be blunted.

Thyroid hormone is highly permissive in angioproliferative pulmonary hypertension in rats

“…2h). Because hypoxia can affect the secretion of thyroid hormones and can also cause changes in plasma levels of thyroxin [20][21][22], we tested whether the combination of SU5416 plus administration of thyroxin (however, without hypoxia) caused pulmonary vascular remodelling and PH. Our data demonstrate that chronic administration of thyroxin alone only causes mild PH in SU5416-treated rats ( fig.…”

Serum testosterone levels and excessive erythrocytosis during the process of adaptation to high altitudes

“…Recent studies have also shown that prolonged exposure to high-altitude hypoxia (3-4 days at 4350 m) does not affect the hypophyseal response to hypothalamic hormones. 104 Human chorionic gonadotropin hormone (hCG) acts on Leydig cells in the luteinizing hormone receptors. At HA (4340 m), low urinary excretion of testosterone after intramuscular injection of 2500 IU hCG has been observed.…”

Endocrine Function

“…Many factors have been proposed to modify the hormone levels in hypoxia, but most theories are still speculative. We conclude that exposure to acute hypoxia induces various changes in hormonal levels, but the hypophyseal response to hypothalamic factors does not appear to be blunted [ 30 ].…”

“…[ 18 ] exposed to 4,350 m and a blunted response to GHRH was found in some subjects [ 30 ]. The concentration of IGF-1 was elevated [ 54 ] or unchanged [ 30 ] at high altitude while the binding protein IGFBP-3 was unchanged [ 30 , 54 ]. However, in subjects exposed for 3 weeks at 6,542 m, IGF-1 was normal [ 70 ], as well as in marathon runners at 4,000 m [ 113 ].…”

“…Hypothalamic factors play a major role in the regulation of all the hypophyseal hormones and a malfunction of this axis could possibly explain the observed altitude-induced alterations [ 30 ]. In a recent study, the responses of TSH, thyroid hormones, prolactin, sex hormones, and GH to injection of TRH, GnFlH, and GRH were studied in eight men in normoxia and on acute exposure to an altitude of 4,350 m (Table 12.1 ).…”