Large variation in steroid concentrations and insulin-like growth factor binding proteins exists among individual small antral follicles collected from within cows at random stages of the estrous cycle1

Abstract

Variation in the biochemical status of individual small (< or = 5 mm diameter) antral follicles within the ovaries of a cow at any given time likely influences the capacity for undergoing recruitment, selection, and establishing dominance. The objectives of this study were to provide insight into the magnitude of variation in follicular fluid concentrations of steroids and activities of IGFBP that exists among individual small antral follicles within and between cows, and to determine the relationships between follicular fluid IGFBP and steroid concentrations in these follicles. A total of 108 small antral follicles were collected from 6 cows at random stages of the estrous cycle, with 10 to 26 follicles/cow. Concentrations of steroids (ng/mL of follicular fluid) in the overall population of follicles ranged from 0.1 (lowest detectable limit) to 51 for estradiol (E2), 4 to 1,149 for progesterone (P4), and 5 to 504 for androstenedione (A4). Concentrations of E2 and A4 were associated positively (r = 0.2; P < 0.02), but E2 (r = -0.4) and A4 (r = -0.4) were associated negatively, with P4. The proportion of variation in steroid concentrations accounted for by differences among animals (P < 0.05) was small for E2 (12%), moderate for P4 (43%), and greatest for A4 (74%). Least differences between minimum and maximum concentrations of steroids observed in follicles from within a cow were 21-, 5.5-, and 3.5-fold for E2, P4, and A4, respectively, whereas the greatest differences between minimum and maximum concentrations were 505-, 108-, and 26-fold for E2, P4, and A4, respectively. Ranges of IGFBP concentrations (arbitrary densitometer units) detected in fluid from a sub-sample of 43 follicles were 1.18 to 4.50 for IGFBP-3, 0.54 to 4.68 for IGFBP-2, 0.07 to 2.56 for IGFBP-4, and 0.01 to 6.71 for IGFBP-5. Concentrations of E2 were correlated negatively with each IGFBP (r = -0.4 to -0.8; P < 0.05) except IGFBP-3. In contrast, concentrations of A4 were correlated positively with IGFBP-3 (r = 0.4; P < 0.05) but were not correlated with other IGFBP. Concentrations of P4 were correlated positively (r > 0.4; P < 0.05) with IGFBP-4 and -5. The results indicate that steroid concentrations and IGFBP activities vary substantially among small antral follicles collected from within and among individual animals and that increasing production of E2, the hallmark of a developing follicle, was associated with reduced activity of all IGFBP except IGFBP-3, thereby implicating these IGFBP in the regulation of follicular recruitment.

Obligatory roles for follicle-stimulating hormone (FSH), estradiol and androgens in the induction of small polyfollicular ovarian cysts in hypophysectomized immature rats

“…Similarly, although values do not appear to be available for A4 concentrations in rat follicular fluid, concentrations of A4 in the follicular fluid of small to medium sized follicles from other mammalian ovaries can be 20-500 ng/ml and increase further in preovulatory follicles [42][43][44][45]. Therefore, as with E2, the concentrations of A4 in the sera of HYPOXD rats bearing A4 pellets appears to be within the expected physiologic range for small and medium sized follicles.…”

“…Ovarian-produced steroids display concentrations in mammalian follicular fluid that are routinely 20-to 1,000-fold greater than their concentrations in peripheral serum [41][42][43][44][45][46]. The amount of steroid observed in the peripheral serum of the HYPOXD rats bearing steroid pellets appears to be within the physiologic range for rats.…”

Effects of feeding high-linoleate safflower seeds on postpartum reproduction in beef cows1,2

“…Aliquots of serum and follicular fluid were evaluated by ligand blotting to determine relative quantities of IGFBP (Laemmli, 1970;Clapper et al, 1998; CV = 15.6%). Insulin-like growth factor binding protein detected in the serum and follicular fluid included a 40-to 43-kDa protein (presumed to be IGFBP-3; Echternkamp et al, 1994), a 34-kDa protein (IGFBP-2; Echternkamp et al, 1994), a 32-kDa protein (IGFBP-1; Kostecka and Blahovec, 1999), a 29-kDa protein (IGFBP-5;Funston et al, 1995a,b;Rempel and Clapper, 2002), and a 25-kDa protein (IGFBP-4; Roberts et al, 2006).…”