Objective: Ovine pregnancy is associated with elevated levels of nitric oxide. Nitric oxide stimulates cyclic guanosine monophosphate (cGMP), which results in vascular smooth muscle relaxation/vasodilation. Phosphodiesterase type 5 regulates cGMP in the urogenital track. The present study was designed to determine message expression of phosphodiesterase type 5 in the myometrium, uterine vessels, and placentome of the sheep and phosphodiesterase type 5 protein expression in the maternal and fetal placentome.
Study design: Tissue was collected from 5 nonpregnant and 5 pregnant anesthetized animals (gestational day = 134 +/- 4) and frozen at -80 degrees C. Optimized reverse transcription-polymerase chain reaction was performed on all tissues, and immunohistochemistry was performed on the placentome only.
Results: Phosphodiesterase type 5 messenger ribonucleic acid levels were significantly higher in the myometrium and placentome, compared with the maternal blood vessels. Phosphodiesterase type 5 protein was immuno-localized to the vascular smooth muscle of the maternal vessels, stroma, and placental capsule only.
Conclusion: Although phosphodiesterase type 5 messenger ribonucleic acid was present in the fetal placenta, phosphodiesterase type 5 protein was expressed only in maternally derived placental tissue. This suggests that regulation of cGMP levels and vascular tone in the umbilical circulation differs from the uterine circulation.