Occupied and unoccupied FSH receptors in follicles of cyclic, hypophysectomized or hypophysectomized/gonadotropin-treated hamsters

Effect of azaline B on follicular development and functions in the hamster

The usefulness of azaline B, a GnRH antagonist, in suppressing gonadotropin secretion in the golden hamster was examined by examining follicular development, steroidogenesis and expression of steroidogenic enzymes. Serum levels of P and E declined significantly, while FSH or LH was undetectable in azaline B-treated hamsters. FSH significantly increased serum E levels, whereas LH upregulated serum P levels. The formation of antral follicles ceased in azaline-treated hamsters, but was reversed by FSH with or without LH supplement. FSH also activated the primordial follicle pool resulting in increased formation of primary and preantral follicles. Further, an increasing trend in the formation of preantral follicles in response to E or E + P, and the formation of antral follicles in response to E + P treatment was evident. The level of Cyp11a1 mRNA increased markedly in LH- or LH + FSH-treated hamsters, whereas FSH with or without LH upregulated Cyp17a1, Cyp19a1 and Fshr mRNA expression. E without or with P also upregulated ovarian Cyp19a1 mRNA expression. The expression of enzyme protein corroborated the mRNA data. In summary, azaline B is an efficient GnRH antagonist in the hamster, and will be useful in studying the selective effect of gonadotropins on ovarian functions without disrupting the physiological functions of other hormones in ovarian cells.

The ability of the aryl hydrocarbon receptor to regulate ovarian follicle growth and estradiol biosynthesis in mice depends on stage of sexual maturity

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxicity of environmental chemicals and regulates many physiological functions, including processes in female reproduction. Previous studies demonstrated that Ahr deletion leads to slow ovarian follicle growth because of impaired estradiol production and reduced gonadotropin responsiveness in prepubertal mice. These studies, however, did not determine how Ahr deletion impairs estradiol production or whether the effects of Ahr deletion on follicle growth and estradiol production persist in adulthood. Thus, the present study evaluated the effect of Ahr deletion on steroid precursors in the estradiol biosynthesis pathway. Furthermore, this study evaluated follicle growth and estradiol biosynthesis in wild-type (WT) and Ahr knockout (AhrKO) antral follicles at different stages of sexual maturity. AhrKO antral follicles from prepubertal mice had slower growth, produced lower estradiol levels, and had reduced cyclin D2 (Ccnd2) expression compared to WT follicles. AhrKO follicles from adult mice, however, produced higher androgen levels and expressed higher levels of Ccnd2 compared to WT follicles. Furthermore, AhrKO follicles from adult mice had growth to that of WT follicles. These findings suggest that the AHR regulates follicle growth by altering factors involved in the estradiol biosynthesis pathway as well as key regulators of follicle growth and that this role of AHR depends on stage of sexual maturity.

Deoxyribonucleic acid polymerase-alpha activity in hamster follicles during the estrous cycle: roles of follicle stimulating hormone and luteinizing hormone

In the hamster, DNA polymerase-alpha (Pol-alpha) in follicles at stages 1-4 (1-4 layers granulosa cells and no theca) increased significantly during the proestrous (P) gonadotropin surges, remained high on estrus (E) and then declined to low levels by 09.00 h, proestrus (P). However, Pol-alpha in stages 5-8 (large preantral to small antral stages) remained steady throughout the cycle. Hypophysectomy on metestrus decreased Pol-alpha by 17 h which was reversed by 2.5 micrograms follicle stimulating hormone (FSH) but not by luteinizing hormone (LH) (2.5 micrograms) or human chorionic gonadotropin (hCG) (1 IU). Hypophysectomy on E resulted 72 h later in a fall in Pol-alpha in stages 1-6; FSH (2.5 micrograms) or LH (2 micrograms) restored enzyme activity within 5 h to stages 1-6 and 5-6, respectively. Thus, Pol-alpha in the smallest preantral follicles is induced by FSH; however, for large preantral and antral follicles, steady levels are maintained by tonic FSH and LH resulting in no apparent change in enzyme activity during active DNA synthesis.

Role of luteinizing hormone in luteotropic complex of pregnant hamster

Hamsters were hypophysectomized on day 4 of pregnancy (day 1 = sperm in vaginal smear) and injected subcutaneously on days 4-7 with various combinations of 200 micrograms prolactin (Prl), 10 micrograms follicle-stimulating hormone (FSH), and 20 micrograms luteinizing hormone (LH) in polyvinylpyrrolidone (PVP) to decrease its rate of absorption or in saline. End points for luteal function on day 8 were maintenance of pregnancy, serum progesterone (P4), luteal weight, and luteal binding for human chorionic gonadotropin, FSH, and Prl. After hypophysectomy, a drastic decline occurred in all parameters including an 89% decrease in luteal weight. Injection of Prl did not maintain pregnancy nor serum P4 but partially maintained luteal weight and human chorionic gonadotropin binding sites per corpus luteum. The minimal luteotropic complex of Prl and FSH was effective in maintaining pregnancy and significantly increased serum P4 and Prl and FSH receptors but not to control levels; Prl and LH (PVP) was also effective to the same extent. Antral follicles were lacking after either treatment. The effects of FSH cannot be attributed to LH contamination. All variables were restored to control levels by Prl plus FSH plus LH (PVP) and antral follicles were present; Prl plus FSH plus LH (saline), however, induced luteolysis and reduced most values to the levels found in untreated, hypophysectomized animals. Thus, the luteotropic activity of LH was only demonstrable when it was injected in a long-acting form; when delivered as a bolus, LH (saline) was luteolytic.

Histological assessment of follicular development and its applicability to risk assessment

The objective of this article is to describe histological methods currently used to study ovarian physiology that may have applicability to reproductive toxicology. Histologic techniques are, for the most part, inexpensive and easy to perform. Many of these techniques require little equipment and can be readily implemented in small laboratories. The resulting histological preparations are permanent, can be used over again for several different types of analyses, and provide objective, quantifiable endpoints. These techniques have been extremely useful for studying the ovary.