Expression and localization of hypoxia inducible factor-1alpha mRNA in the porcine ovary

Angiogenesis is an essential process during follicular development and corpora lutea (CL) formation. Recent studies have shown that vascular endothelial growth factor (VEGF) is an essential regulator of ovarian angiogenesis. Several lines of evidence have indicated that the production of VEGF is regulated by hypoxia inducible factor-1alpha (HIF-1alpha), especially under hypoxic conditions, but the expression of HIF-1alpha has not been well characterized in the porcine ovary. The present study examined the expression of HIF-1alpha mRNA and its localization in porcine ovaries at different stages of the estrous cycle. Northern blot analyses of total CL RNA indicated hybridization of the porcine HIF-1alpha probe to transcripts of approximately 3.8 kb. The mRNA expression of HIF-1alpha was highest in CL during the early luteal phase, followed by a decrease during the mid- and late-luteal phases. Using in situ hybridization, abundant HIF-1alpha mRNA was evident in follicles and CL. Within non-atretic follicles, HIF-1alpha mRNA was highly expressed in the granulosa cell layer, while weaker labeling was evident in the theca interna. These results suggest that HIF-1alpha may play a role in the regulation of cellular metabolism and blood supply during follicular growth and CL formation.