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.