Regulation of bovine cervical secretion of prostaglandins and synthesis of cyclooxygenase by oxytocin

Prostaglandin E₂ (PGE₂) can cause softening of the bovine cervix at oestrus when receptors for oxytocin (OT) are maximally present, indicating a relationship between OT and PGE₂ production. It was therefore determined whether OT can stimulate prostaglandin synthesis or induce cyclooxygenase expression in cervical external os segments obtained from pre-oestrous- oestrous cows. Tissues were minced and incubated (50-100 mg mL^-1 6 h^-1) in the presence of OT (10 ng mL^-1), progesterone (P₄) (5 ng mL^-1) and/or indomethacin (5 μg mL^-1). It was found that OT stimulated basal PGE₂ (7.794±1.22 ng 100 mg^-1, mean±s.e.m.; n = 6) in external os segments from pre-oestrous-oestrous cows (P < 0.03), whereas P₄ and indomethacin inhibited basal and OT-stimulated PGE₂ production (P < 0.05). Basal prostaglandin F(2α) (PGF(2α)) production was minimal (<1 ng 100 mg^-1) and OT had no effect on its production. Expression of cyclooxygenase was measured by Western blot analysis following incubation of the tissue (100mg 1.5mL^-1 3 h^-1) in the presence of OT (10ng mL^-1) and in the presence of P₄ (5 ng mL^-1). It was found that OT stimulated the induction of cyclooxygenase II (79±10%; n = 7, P < 0.05). In contrast, P₄ inhibited the basal expression of this enzyme (-40±5%, n = 7, P < 0.05) in the presence or absence of OT. It is concluded that, in vitro, OT stimulates PGE₂ synthesis by the bovine cervix at oestrus and that this effect is mediated by cyclooxygenase.