Human preovulatory follicular fluid: the lipids. Are they the trigger for capacitation?

The lipid content of human follicles within 6 h of ovulation was determined. Levels for triglycerides, phospholipids, and total cholesterol were 1/4 to 1/3 of those in serum. An uncommonly high level of free cholesterol was observed, possibly resulting from a high synthetic rate by the granulosa. Follicular lipids appear to be of serum origin since the relative proportions of the various fatty acids are the same. Arachidonic acid was not found to be present at the high levels reported for "large" porcine follicles, possibly due to its active utilization in the synthesis of prostaglandins necessary for the ovulation process. Precise timing relative to ovulation is clearly essential for follicular classification in order to distinguish between before and after the triggering of the ovulation process. A possible role for lipids in the induction of capacitation is proposed.