Nitric oxide (NO) plays an important role in
prostaglandin secretion and angiogenesis in the reproductive system. In the present study, the roles of the NO donor
spermine NONOate and tumour
necrosis factor-alpha (TNF; as a positive control) in
prostaglandin production and angiogenic activity of equine endometria during the oestrous cycle were evaluated. In addition, the correlation between NO production and the expression of key
prostaglandin synthase proteins was determined. The
protein expression of
prostaglandin F synthase (PGFS) increased in early and mid-luteal stages, whereas that of
prostaglandin E synthase (PGES) was increased in the early luteal stage. The in vitro release of NO was highest after ovulation. There was a high correlation between NO production and PGES expression, as well as NO release and PGFS expression. There were no differences detected in
prostaglandin H synthase 2 (PTGS-2) throughout the oestrous cycle and there was no correlation between PTGS-2 expression and NO. In TNF- or
spermine-treated endometria, the expression of
prostaglandin (PG) E(2) increased in the early and mid-luteal phases, whereas that of
PGF(2alpha) increased in the follicular and late luteal phases. Bovine aortic endothelial cell (BAEC) proliferation was stimulated in TNF-treated follicular-phase endometria. However, in
spermine-treated endometria, NO delivered from its donor had no effect, or even an inhibitory effect, on BAEC proliferation. In conclusion, despite no change in PTGS-2 expression throughout the oestrous cycle in equine endometrial tissue, there were changes observed in the expression of PGES and PGFS, as well as in the production of
PGE(2) and
PGF(2alpha). In the mare, NO is involved in the secretory function of the endometrium, modulating
PGE(2) and
PGF(2alpha) production. Even though TNF caused an increase in the production of angiogenic factors and
prostaglandins, its complex action in mare uterus should be elucidated.