Insulin-like growth factor-binding protein-2 and -3 are correlated with atresia and preovulatory maturation in the porcine ovary

Abstract

We compared insulin-like growth factor-binding protein (IGFBP) levels with indicators of follicular maturation and atresia in individual follicles of the porcine ovary. Follicular development was synchronized with the progestin, altrenogest, and progestin withdrawal was used to initiate the growth of an ovulatory cohort of follicles, which is accompanied by atresia of noncohort follicles. Individual follicles were isolated on days 1, 3, 5, and 7 after progestin withdrawal. Atretic follicles were identified by the presence of low hypodiploid levels of DNA in 10% or more of their granulosa cells using flow cytometry. The follicular fluid (FF) level of IGFBP-3 did not differ significantly between healthy and atretic medium-sized (3- to 6-mm) follicles and was not significantly correlated with the percentage of granulosa cells containing hypodiploid levels of DNA (r = 0.181) or with endocrine parameters such as FF concentrations of estradiol or androstenedione. However, among healthy follicles (atretic follicles removed from analyses to better examine follicular maturation), IGFBP-3 increased (P < 0.01) between days 1 and 7 and was positively correlated with follicle diameter (r = 0.514; P < 0.05) and the FF concentration of progesterone (r = 0.556; P < 0.01), indicators of the degree of follicular maturation. FF IGFBP-2 levels were 3-fold greater (P < 0.01) in atretic than in healthy follicles, and IGFBP-2 was correlated with percentage of granulosa cells containing hypodiploid levels of DNA (r = 0.729; P < 0.001). Among healthy follicles, FF IGFBP-2 did not differ significantly among days and was not significantly correlated with follicle diameter. These data suggest that the content of IGFBP-2 is related to the state of follicular health/atresia, whereas IGFBP-3 is related to preovulatory follicular development.

Ovarian expression of insulin-like growth factor-I (IGF-I), IGF binding proteins, and growth hormone (GH) receptor in heifers actively immunized against GH-releasing factors.

“…In the present study levels of lGFBP-2 in FFL from small follicles were increased by GRFi while IGFBP-3 levels were decreased. Recently Grimes et al (41) reported a positive correlation between FFL lGFBP-3levels and follicle diameter in the porcine ovary (41). In contrast, lGFBP-2 was found to be related more to atresia than to follicle size, suggesting specific roles for individual forms of lGFBP.…”

Insulin-Like Growth Factor-Binding Proteins and Ovarian Folliculogenesis

“…2). By contrast, in sheep and pig, growth of follicles is characterized by a slight increase in intrafollicular IGFBP-3 levels [19,21], Moreover, in the sheep, atresia of small follicles is characterized by a decrease in intrafollicular IGFBP-3 levels [21 ]. The mech anisms that lead to such observed changes in intrafollicu lar IGFBP-3/IGFBPs<40 kD ratio are likely different for IGFBPs <40 kD and IGFBP-3.…”

Follicle-Stimulating Hormone and Insulin-Like Growth Factor-I Attenuate Apoptosis in Cultured Porcine Granulosa Cells1

“…We have described the changes in concentration of ovarian steroids and in expression of several peptides associated with apoptosis and cell proliferation in vivo during two stages of follicular development in pigs [7,[10][11][12][13][14][15][16]. However, in vitro model systems are needed for pigs for the investigation of factors that regulate proliferation and death at the cellular level.…”