Changes in linoleic acid during follicular development and inhibition of spontaneous breakdown of germinal vesicles in cumulus-free bovine oocytes

Abstract

The fatty-acid composition of follicular fluid from small and large developing follicles was analysed and the effects of saturated and unsaturated fatty acids on spontaneous breakdown of germinal vesicles were investigated. Fatty acids were bound to bovine serum albumin and cultured with oocytes at 100 μmol/l. Linoleic acid (18:2) was the only fatty acid tested that significantly inhibited breakdown of germinal vesicles (P < 0.01). The effect was dose-dependent and was greatest at 50 μmol fatty acid/l (% breakdown of control, 81.1 ± 6.8 vs. 50 μmol linoleic acid/l, 35.4 ± 7.3: P < 0.02). Linoleic acid was the major fatty acid, constituting about a third of the total fatty acid in the follicular fluid, followed by 18.9 ± 1.0% and 16.9 ± 1.3% oleic acid (18:1) in small and large follicles, respectively. Saturated fatty acids accounted for <30% of the total fatty acid composition. There was a marked absence of tetraenoic acids in small and large follicles. Proportions of linoleic acid were significantly lower in follicular fluid from large follicles (31.1 ± 1.2% of total fatty acid) than from small follicles (34.8 ± 0.7% of total fatty acid) (P < 0.05) and there was a significant inverse correlation between follicle diameter and percentage of linoleic acid in the follicular fluid (r = -0.6966: P < 0.05). There was no significant alteration in any other fatty acid during follicular development. The results suggest that (i) a critical relative concentration of linoleic acid may be required for maintenance of meiotic arrest in bovine oocytes and (ii) the decline in the proportion of linoleic acid during follicular development may contribute to the relief of the inhibition of breakdown of germinal vesicles.