Vascular characteristics and expression of hypoxia genes in Tibetan pigs' hearts.

Background: Tibetan pigs have exhibited unique characteristics from low-altitudes pigs and adapted well to the Qinghai-Tibet Plateau.

Objectives: The current study was undertaken to investigate the hypoxic adaptation of heart in Tibetan pigs.

Methods: The hearts of Tibetan pigs and Landrace pigs raised at high or low altitudes were compared using 3D casting technology, scanning electron microscopy and real-time quantitative PCR (qRT-PCR).

Results: We found that the ratio of the major axis to the minor axis and the density of the heart were significantly higher in Tibetan pigs than in Landrace pigs (p < 0.05). Tibetan pigs had larger diameters and higher densities of arterioles than Landrace pigs (p < 0.05), and these features have a similar variation with the expression of vascular endothelial growth factor (VEGF). The cardiac expression levels of hypoxia-inducible factor-1α (HIF-1α) and endothelial nitric oxide synthase (eNOS) were significantly higher in pigs reared at high altitudes than in those reared at low altitudes (p < 0.05). In contrast, Egl nine homolog 1 (EGLN1) had the opposite trend with respect to HIF-1α and eNOS and was related to red blood cell (RBC) counts. Notably, the expressions of erythropoietin (EPO) and endothelial PAS domain-containing protein 1 (EPAS1) were significantly higher in Landrace pigs kept at high altitudes than in the others (p < 0.05) and were associated with haemoglobin.

Conclusions: These findings show that the regulation of the heart function of Tibetan pigs in a hypoxic environment is manifested at various levels to ensure the circulation of blood under extreme environmental conditions.