Endocrine Abstracts

Polyunsaturated fatty acids (PUFA) act as precursors for prostaglandin (PG) synthesis. PGs both inhibit and stimulate ovarian steroidogenesis. We have therefore examined the hypothesis that high n-3 PUFA diets affect ovarian steroid synthesis through modulating prostaglandin synthesis.

Welsh mountain ewes were individually fed a control diet or a diet containing linseed (high in n-3 PUFA) for 6 weeks. To assess the impact of the diet during different stages of the oestrous cycle, ewes were slaughtered during either the early (days 4–5: n=8) or late luteal phase (day 14: n=9) of the cycle. Blood samples were collected for the analysis of plasma progesterone (P4), and 13,14-dihydro-15 keto prostaglandin F_1α (PGFM: the stable metabolite of prostaglandin F_2α) by specific immunoassays. Ovarian and uterine tissue lysates were analysed by western blotting for expression of key regulators of PG (cyclooxygenase-2: COX-2) and steroid hormones (steroidogenic acute regulatory protein: StAR) synthesis.

The high n-3 PUFA diet significantly decreased the number of PGFM peaks between days 13–16 (control ewes: n=6, 6.2±0.48; n-3 ewes: n=8, 3.9±0.74, P<0.05) and increased the levels of P4 (ng/ml) on days 14.5–16 (control ewes: n=6, 0.32±0.12; n-3 ewes: n=5, 0.71±0.15, P<0.05) of the oestrous cycle. Moreover, on days 4–5 of the oestrous cycle, levels of expression of StAR and COX-2 were significantly lower in ovaries as was uterine expression of COX-2 on day 14 from n-3 PUFA fed animals. We therefore conclude that a high n-3 PUFA diet extends the luteal phase of the oestrous cycle by inhibiting uterine release of PGF_2α (through inhibiting uterine COX-2 expression). The effects of the PUFA diet on StAR expression may be either direct or indirect due to lack of luteotrophic support from prostaglandin E₂ as a consequence of decreased ovarian COX-2 expression.

Supported by the Wellcome Trust and BBSRC.