SUMMARY: The study was carried out at two different altitudes in the southern region of Saudi Arabia: Abha, 2,800 meters above sea level, the high altitude (HA) area and Jazan, 40 meters above sea level the low altitude (LA) area. Following exposure to high altitude, testes of rats revealed various types of atrophy and degeneration in the seminiferous tubules and in the interstitial tissue. There was detachment of the basal laminae of the tubules and a profound decrease in cellularity. When rats were brought back to their habitat (LA) and later examined, many tubules showed normal population of cells including spermatids and spermatozoa. Well-arranged epithelium was seen in most of the seminiferous tubules of these animals, normal interstitial space and no detachment of the basal lamina. Apparently complete recovery had been achieved ultrastructurally, in hypoxic group; some spermatogenic cells lost their normal architecture, being irregular in shape with some features of necrosis, such as shrinkage and pyknotic nuclei characterized by chromatin condensation. Significant decrease in epithelial height was noticed in these animals (P <0.05). Also, the diameter of the tubules showed slight decrease with concomitant increase in interstitial spaces.
KEY WORDS: High altitude; Low altitude; Hypoxia; Semen; Reproductive hormones.