This study compared lipoprotein phospholipid, cholesterol, protein, and glycosaminoglycans in the lipoprotein fraction among follicular fluid pools derived from 2633 small (less than 6 mm), 1702 medium (6 to 10 mm), and 491 large (11 to 20 mm) bovine follicles subdivided by estradiol-17 beta concentrations. High density lipoproteins were the only lipoprotein class found in follicular fluid when apolipoprotein profile of the less than 1.21 g/ml density fraction was analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis and silver staining. Within a follicular size class, concentrations of lipoprotein constituents did not change among follicular fluid pools with varying estradiol-17 beta concentrations. As follicular size increased, follicular fluid lipoprotein phospholipid, cholesterol, and protein significantly increased. The percentage of total follicular fluid glycosaminoglycans in the less than 1.21 g/ml density fraction was highest for small follicles but averaged less than 5% for all follicular size classes. Therefore, bovine follicular fluid contains only high density lipoproteins and concentrations increased with follicular maturation. That increase in high density lipoprotein could be a potentially important source of cholesterol for progesterone production after the LH surge.

The glycosaminoglycans chondroitin sulfate (CS) and heparan sulfate (HS) are present in follicular fluid. The present study evaluated estradiol (E), progesterone (P), CS, and HS concentrations from pools of 2633 small (less than 6 mm), 1702 medium (6-10 mm), and 491 large (greater than 10 mm) bovine follicles subdivided by relative E concentrations. E and P concentrations increased with follicle enlargement (P less than 0.05), but were inversely related within a follicle size. CS levels were reduced (P less than 0.05) in large (0.84 mg/ml) compared to small (1.18 mg/ml) and medium (1.36 mg/ml) follicles, while HS levels were decreased (P less than 0.05) in medium (0.34 mg/ml) and large (0.19 mg/ml) compared to small (1.10 mg/ml) follicles. Within a follicle size, CS and HS levels decreased significantly with increasing E. CS to HS ratios increased with follicle size and E concentration. The ratio of CS to HS was 4.4- and 1.6-fold higher, respectively, in medium and large follicular fluid samples classified healthy compared to atretic by their E content. These results support the idea that concentrations of glycosaminoglycans decrease with follicular maturation, and atretic follicles contain elevated levels of CS and HS.

Possible interactions between glycosaminoglycans and high density lipoproteins (HDL) in plasma and follicular fluid were examined. Total lipoproteins (d less than 1.21 g/ml) were obtained from plasma of five Holstein cows by ultracentrifugation and fractionated by gel filtration. Every other fraction from the HDL peak or fractions corresponding to the base and ascending portion of the HDL peak were composited and applied to a heparin-Sepharose affinity chromatography column. Elution profiles from both composites showed a peak that did not bind to the column that contained HDL devoid of apolipoprotein-E as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining and immunoblot analysis. Elution of lipoproteins from the ascending portion of the HDL peak resulted in a second minor peak eluting at 0.35 M NaCl, which was low density lipoprotein (LDL) contamination. Lipoproteins (d less than 1.21 g/ml) isolated from follicular fluid obtained from small, medium or large follicles also were subjected to heparin-Sepharose affinity chromatography. Two peaks were observed, one corresponding to the lipoprotein that did not bind to the column, the other eluted at 0.5 M NaCl and accounted for less than 2% of the protein applied. The second peak did not contain apolipoprotein-E or LDL. Bovine follicular fluid glycosaminoglycans (GAG) were isolated and subjected to HDL-Sepharose affinity chromatography. Less than 2% of the total GAG bound to the HDL column. Therefore, HDL in bovine specimens did not interact appreciably with heparin or GAG isolated from follicular fluid.

Concentrations of estradiol-17 beta in follicular fluid were correlated to follicular size, stage of estrous cycle, location of corpus luteum, and presence of large follicles. Paired ovaries were obtained from 481 nonpregnant cows at slaughter and follicles were classified as ipsilateral or contralateral to the corpus luteum. Follicular fluid estradiol-17 beta concentrations from 2494 small, 1485 medium, and 396 large follicles were quantified by radioimmunoassay. Stage of estrous cycle was estimated by visual examination of the corpus luteum. Follicles in stage 1 of the estrous cycle (d 1 to 4) had the highest estradiol-17 beta concentration and the smallest mean follicular diameter. Location of follicles relative to the corpus luteum had no influence on estradiol-17 beta concentrations. As follicular size increased, concentration of estradiol-17 beta also increased. The presence of a single large follicle did not affect the concentration of estradiol-17 beta in medium or small follicles. In contrast, if multiple large follicles occurred in the same cow, concentrations of estradiol-17 beta were significantly lower in medium but not small follicles.