Cation and Protein Composition of Ovarian Follicular Fluid of the Pig: Relation to Follicle Size

Abstract

Follicular fluid was collected from dissected as well as undissected follicles of the pig. Follicular fluid volume and ovarian follicle weight were highly correlated and this correlation was used to estimate follicular size of undissected follicles. Concentrations of sodium, potassium, calcium, and protein were measured in follicular fluids taken from various-sized ovarian follicles. Mean concentrations (mM) of the atoms in the follicular fluid were Na (128.4 ± 4.5), K (15.9 ± 0.06), and Ca (2.34 ± 0.04). Protein concentration in the follicular fluid was 65 mg/ml. Relative to previous reports of serum concentrations of these ions the follicular fluid was K rich and Na poor. Furthermore, the concentrations of the ions and protein remained stable over the range of follicle sizes analyzed, although all components were negatively correlated with increasing size of ovarian follicle. The largest follicles analyzed contained a concentration of K approximately one-half that seen in all other sized follicles. Regression analyses indicated that the decreased amounts of Ca and K were statistically significant. Removal of ovarian follicles from the ovary and subsequent incubation in physiological saline (9% NaCl) resulted in the loss of calcium ions from the follicular fluid. These data indicate that a major portion of follicle growth occurs without marked alterations in the concentrations of the osmotically active atoms, Na and K. However, the elevated levels of K atoms in the follicular fluid may indicate that secretory mechanisms are involved in fluid accumulation. The significance of these results to the process of follicular fluid accumulation are discussed.