Concentrations of High Density Lipoproteins Vary Among Follicular Sizes in the Bovine

Abstract

This study compared lipoprotein phospholipid, cholesterol, protein, and glycosaminoglycans in the lipoprotein fraction among follicular fluid pools derived from 2633 small (<6mm), 1702 medium (6 to 10mm), and 491 large (11 to 20mm) bovine follicles subdivided by estradiol-17β concentrations. High density lipoproteins were the only lipoprotein class found in follicular fluid when apolipoprotein profile of the <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-17β concentrations. As follicular size increased, follicular fluid lipoprotein phospholipid, cholesterol, and protein significantly increased. The percentage of total follicular fluid glycosaminoglycans in the <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.