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

Prostaglandin E-2 (PGE(2)) can cause softening of the bovine cervix at oestrus when receptors for oxytocin (OT) are maximally present, indicating a relationship between OT and PGE(2) 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 (P-4) (5 ng mL(-1)) and/or indomethacin (5 mu g mL(-1)). It was found that OT stimulated basal PGE(2) (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 P-4 and indomethacin inhibited basal and OT-stimulated PGE(2) production (P < 0.05). Basal prostaglandin F-2 alpha (PGF(2 alpha)) 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 Pq (5 ng mL(-1)). It was found that OT stimulated the induction of cyclooxygenase II (79+/-10%; n = 7, P < 0.05). In contrast, Pq 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 PGE(2) synthesis by the bovine cervix at oestrus and that this effect is mediated by cyclooxygenase.