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

Abstract

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 (7·79 ± 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 (100 mg 1·5 mL^-1 3 h^-1 ) in the presence of OT (10 ng 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.