Effects of leptin on HPG axis and reproductive function in male rat in simulated altitude of 5500 m hypoxia environment.

High altitude hypobaric hypoxia environment impairs male's reproductive function. Leptin is an adipose tissue-derived hormone which regulates body weight homeostasis. Its receptor (LepR) has been found in all levels of male reproductive axis, indicating that it can affect male reproductive system in a direct or (and) indirect way. However, the role of leptin signaling in hypobaric hypoxia induced male reproductive dysfunction remains to be elucidated. In this study, we investigated the changes of leptin levels in male SD rats in stimulated altitude of 5500 m hypobaric hypoxia environment and their effects on the hypothalamus-pituitary-gonad axis (HPG axis). A hypoxia animal model was established using a hypobaric hypoxia chamber. Rats were divided randomly into 1, 7, 14, 28-day hypoxia group, recovery group (14 days hypoxia+14 days normoxia) and their control groups. Hypoxia groups displayed obvious changes of testicular and epididymis index compared to control groups. The total number of sperm and sperm motility rate decreased dramatically, while sperm deformity rate increased in hypoxia groups. The flow cytometry analysis showed that the percentage of haploid in 1-day, 7-day and 28-day hypoxia groups increased while the proportion of diploid decreased in 14-day and 28-day hypoxia group. TUNEL staining showed that the testis cells apoptosis index (AI) of hypoxia groups increased significantly, and the apoptosis of cells mainly focus on spermatogonia and spermatocytes. The expression of GnRH in hypothalamus decreased dramatically under hypoxia condition, accompanied with the reduction of serum testosterone (T) level in 1-day and 28-day hypoxia groups and free-testosterone level (FT) in 1-day and 14-day hypoxia groups. Importantly, ELISA analysis showed that serum leptin level decreased in 7-day hypoxia groups and acylated-ghrelin, gastrin also changed, accompanying with reduction of LepR in hypothalamus in hypoxia groups. Immunohistochemical staining exhibited increased leptin and LepR in testis under hypobaric hypoxia conditions. Our results suggested that simulated high altitude hypobaric hypoxia environment decreased male reproductive function, depressed HPG axis activity and altered the serum concentration of hormones related to food intake in adult male rats. Additionally, hypobaric hypoxia induced the leptin-LepR expression in adult male rats' testis, suggesting leptin-LepR signaling may mediate hypoxia-induced impairment in male rats' reproductive system.