The amounts of total protein, albumin, fibronectin, alpha 2-macroglobu
lin (alpha 2-M), immunoglobulin G, ceruloplasmin and antithrombin were
determined in fluids collected from 53 preovulatory equine follicles
and compared with the contents of estradiol-17 beta, progesterone and
androstenedione, with follicle size and the amounts of the equivalent
proteins in normal equine plasma. The concentration of fibronectin and
the fibronectin/albumin ratios increased significantly with follicle
size and with follicular estradiol levels. The alpha 2-M levels and al
pha 2-M/albumin ratios correlated with follicle size but not with horm
one content. Both fibronectin and alpha 2-M were present in lower amou
nts in follicular fluid compared with plasma while the other proteins
were present in similar amounts. Among the proteins evaluated, there w
as a positive correlation between the amount of the protein in the fol
licular fluid and the molecular weight of the protein.