Comparison of Follicular Estrogen Receptors in Rat, Hamster, and Pig1

Abstract

The hypophysectomized or intact hamster--unlike the rat--does not respond to estrogen by increasing the number of large antral follicles. In the pig, estrogen inhibits progesterone synthesis by granulosa cells from large follicles for 36 h before progesterone accumulation is enhanced. The objective of this study was to determine whether these divergent responses of the three species to estrogen are related to differences in follicular estrogen receptors. For the rat antral follicle, the equilibrium dissociation constants (Kds), expressed as nmol/L, were 0.55 +/- 0.07 in the cytosolic fraction and 0.46 +/- 0.11 in the nuclear fraction; for the hamster and pig follicles, the respective Kds were 1.08 +/- 0.04 and 0.94 +/- 0.11, and 1.16 +/- 0.23 and 1.09 +/- 0.17, respectively. The cytosolic and nuclear Kds for the rat follicle were statistically different from those of the other two species, but this is most likely not of biological consequence. Comparison of the maximal numbers of binding sites (NBSmax) in the cytosolic fractions of the antral follicles, expressed as fmol/mg protein, indicated a relationship of hamster > rat = pig; whereas in the nuclear fraction, with the NBSmax expressed as fmol/mg DNA, the relationship was hamster > pig > rat. The total number of estrogen receptors (sum of the NBSmax of cytosolic and nuclear fractions) was approximately tenfold higher in the hamster than in the rat. Thus, the failure of hamster large follicles to respond in vivo or in vitro to estrogen cannot be explained on the basis of lack of estrogen receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen Receptor-β Expression in Relation to the Expression of Luteinizing Hormone Receptor and Cytochrome P450 Enzymes in Rat Ovarian Follicles1

“…The beginning of ER␤ mRNA expression in granulosa cells of very small follicles coincides with the expression of FSH receptors in granulosa cells [36][37][38]. In hypophysectomized or immature female rats and mice, estrogen has been shown to stimulate preantral and early antral follicular growth [39][40][41][42][43]. Estrogen is also known to act synergistically with FSH to stimulate LHr expression in granulosa cells [1].…”

Steroid Receptors in the Uterus and Ovary

“…Similar data of a single E2 binding component with a K d = 1-1.4 nM in hamster ovaries is also reported. 413,414 The majority of studies on the regulation of β expression during folliculogenesis focus on the rat ovary. While some report high but relatively constant levels of ERβ mRNA leading up to proestrus, 380 more detailed studies indicate a substantial increase in ERβ expression that peaks in medium sized (275-450 mm) follicles possessing clearly defined antrum.…”

Estrogen Receptor Null Mice: What Have We Learned and Where Will They Lead Us?

“…Therefore, normal ovarian function appears to be dependent on a multitude of auto-and paracrine actions of estradiol that act in concert with the gonadotropins secreted from the anterior pituitary to provide for successful folliculogenesis and steroid production. Nonetheless, immunohistochemical detection and characterization of ER in the different ovarian compartments have proven difficult, although studies employing binding assays with radiolabeled ligands report the presence of ER in ovarian granulosa cells of the rat (216,(233)(234)(235), mouse (236), rabbit (236), and pig (235).…”