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, indic ating a relationship between OT and PGE(2) production. It was therefor e determined whether OT can stimulate prostaglandin synthesis or induc e 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)), progeste rone (P-4) (5 ng mL(-1)) and/or indomethacin (5 mu g mL(-1)). It was f ound 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 co ws (P < 0.03), whereas P-4 and indomethacin inhibited basal and OT-sti mulated PGE(2) production (P < 0.05). Basal prostaglandin F-2 alpha (P GF(2 alpha)) production was minimal (<1 ng 100 mg(-1)) and OT had no e ffect on its production. Expression of cyclooxygenase was measured by Western blot analysis following incubation of the tissue (100 mg 1.5 m L(-1) 3 h(-1)) in the presence of OT (10 ng mL(-1)) and in the presenc e of Pq (5 ng mL(-1)). It was found that OT stimulated the induction o f cyclooxygenase II (79+/-10%; n = 7, P < 0.05). In contrast, Pq inhib ited the basal expression of this enzyme (-40+/-5%, n = 7, P < 0.05) i n the presence or absence of OT. It is concluded that, in vitro, OT st imulates PGE(2) synthesis by the bovine cervix at oestrus and that thi s effect is mediated by cyclooxygenase.