Inactivation of Corticotropin-Releasing Hormone–Induced Insulinotropic Role by High-Altitude Hypoxia

Abstract

We have shown that hypoxia reduces plasma insulin, which correlates with corticotropin-releasing hormone (CRH) receptor 1 (CRHR1) in rats, but the mechanism remains unclear. Here, we report that hypobaric hypoxia at an altitude of 5,000 m for 8 h enhances rat plasma CRH, corticosterone, and glucose levels, whereas the plasma insulin and pancreatic ATP/ADP ratio is reduced. In islets cultured under normoxia, CRH stimulated insulin release in a glucose-and CRH-level-dependent manner by activating CRHR1 and thus the cAMP-dependent protein kinase pathway and calcium influx through L-type channels. In islets cultured under hypoxia, however, the insulinotropic effect of CRH was inactivated due to reduced ATP and cAMP and coincident loss of intracellular calcium oscillations. Serum and glucocorticoid-inducible kinase 1 (SGK1) also played an inhibitory role. In human volunteers rapidly ascended to 3,860 m, plasma CRH and glucose levels increased without a detectable change in plasma insulin. By contrast, volunteers with acute mountain sickness (AMS) exhibited a marked decrease in HOMA insulin sensitivity (HOMA-IS) and enhanced plasma CRH. In conclusion, hypoxia may attenuate the CRH-insulinotropic effect by reducing cellular ATP/ADP ratio, cAMP and calcium influx, and upregulated SGK1. Hypoxia may not affect HOMA-IS in healthy volunteers but reduces it in AMS volunteers.To enjoy social activities, millions of people travel to high altitudes every year. High-altitude hypoxia often induces dysfunction and illness, particularly acute mountain sickness (AMS) (1). During the construction of the QinghaiTibet railway (at altitudes of 3,000-5,000 m) in China, .100,000 construction workers were involved, and 51% of them developed AMS (2). Moreover, since the railway began service, .10 million travelers have visited the Tibet region in 2012, of whom 31% developed AMS despite traveling with an oxygen supply on the train (3). Increasing evidence in both humans and animals suggests that exposure to either high-altitude or hypobaric hypoxia influences plasma insulin levels and glucose homeostasis, depending on the oxygen level and duration of exposure (4-9). We previously showed that subacute hypoxia at an altitude of 5,000 m for 5 days reduces plasma insulin in rats, and this effect is blocked by a corticotropin-releasing hormone (CRH) receptor 1 (CRHR1) antagonist in vivo (10). However, the underlying mechanisms have not been clearly addressed.Insulin, the unique hypoglycemic hormone, plays a crucial role in maintaining glucose sensing in pancreatic b-cells and regulating glucose uptake in a variety of tissues and cells during health and disease (11,12). Apart from glucose, many neural and endocrine hormones regulate pancreatic insulin release (13). In particular, CRH is the key regulator of the hypothalamic-pituitary-adrenal (HPA) axis; is activated by a variety of stressors, including hypoxia; and mediates a variety of neural and endocrine

Glycated haemoglobin (HbA1c) and fasting plasma glucose relationships in sea‐level and high‐altitude settings

“…Glucose metabolism has been shown to differ at altitude; for instance, an association between polycythaemia and glucose intolerance has previously been described in an Andean population [12]. A study in rats showed that exposure to hypobaric hypoxia is associated with reduced insulin release due to inhibition of corticotrophin-releasing hormone [19]. This has also been replicated in clinical research; a recent publication by our group found that a 5% decrease in oxyhaemoglobin saturation was strongly associated with a HbA 1c value ≥ 48 mmol/mol (≥ 6.5%) (Miele C et al personal communication).…”

Systemic pro-inflammatory response facilitates the development of cerebral edema during short hypoxia

“…Rats in the hypoxia group were placed in a hypobaric chamber (Avic Guizhou Fenglei Aviation Armament Co., Ltd, China, FLYDWC-50-IIC) and exposed to hypobaric hypoxia of 7000 m altitude (41.02 kPa, 8.2 % O 2 ) for 1, 4 or 8 h with or without CP154,526 (CRHR1 antagonist, 30 mg/kg, intraperitoneal (ip)) or 5000 m altitude (54.02 kPa, 10.8 % O 2 ) for 2 days [ 19 ]. The normoxia group was placed in the same chamber set at sea level (100.08 kPa, 20.9 % O 2 ).…”

IGFBP2 Plays an Essential Role in Cognitive Development during Early Life

“…[37] Mice at p9, p14, p28, and p35 were deeply anesthetized with ether and decapitated and the hippocampi were removed, immediately frozen in liquid nitrogen, and stored at −80 °C. Control newborn mice were set at sea level (21.0% O 2 ) in a similar chamber.…”