Endocrine Abstracts

Parturition in the ewe is initiated by the fetus following the cortisol rise via activation of the hypothalamic-pituitary-adrenal axis and increased intrauterine PG production. Dietary n-6 PUFAs, noteceably linoleic acid (LA) are the precursors for PG synthesis. The maternal intercotyledonary endometrium is the main site of PGF_2alpha during labour. This study investigated the effect of dietary n-6 PUFA supplementation on uterine PG production at term. Ewes (n=32) were fed either an LA enriched diet or an isoenergetic control diet from day 100 of pregnancy, injected with 0 or 4 mg/50 kg dexamethasone (DEX) i.m. on day 133 and slaughtered on day 135 for collecting IC tissues. The tissues were cultured in serum free DMEM/F12 medium containing 1.125 g/L bovine serum albumin and ITS for 18 h for examining basal PG production before they were challenged with control medium or oxytocin (OT, 250 nM) for 2 and 22 h. PGF_2alpha and PGE₂ in the spent medium were quantified using radioimmunoassays. Statistical analysis was carried out using a split ANOVA (Mixed model) built in SAS. DEX induction enhanced basal PGF_2alpha and PGE₂ production significantly (P<0.05-0.0001) and altered the tissue response to PUFA supplementation. Dietary n-6 PUFA supplementation raised basal PG production significantly in the non-induced group (P<0.05-0.001) but not in the DEX group (P>0.05). OT challenge significantly increased both PGF_2alpha and PGE₂ generation (P<0.05) and the tissue responsiveness to OT was significantly altered by DEX induction and PUFA supplementation. Following OT challenge PUFA supplementation significantly enhanced PGF_2alpha production in both DEX induced and non-induced ewes (P<0.05-0.01). In summary, the study showed that dietary PUFA supplementation and DEX induction altered uterine PG production and response to OT in late pregnant ewes and this may affect both the initiation and progression of parturition.