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Reproduction, Fertility and Development Reproduction, Fertility and Development Society
Vertebrate reproductive science and technology
RESEARCH ARTICLE

In vitro and in vivo regulation of follicular formation and activation in cattle

Joanne E. Fortune A B , Ming Y. Yang A and Wanzirai Muruvi A
+ Author Affiliations
- Author Affiliations

A Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.

B Corresponding author. Email: JF11@cornell.edu

Reproduction, Fertility and Development 23(1) 15-22 https://doi.org/10.1071/RD10250
Published: 7 December 2010

Abstract

The establishment of a stockpile of non-growing, primordial follicles and its gradual depletion through activation of primordial follicles are essential processes for female fertility. However, the mechanisms that regulate follicle formation, the activation of primordial follicles to begin growth and the primary-to-secondary follicle transition are poorly understood, especially in domestic animals and primates. The authors’ laboratory is engaged in studying early stages of follicular development in cattle and this review summarises the progress to date. Bovine follicles begin to form in fetal ovaries around the beginning of the second trimester of pregnancy (about Day 90), but the first activated, primary follicles do not appear until after Day 140. Bovine fetal ovaries produce steroids and production is highest during the first trimester. In vitro, oestradiol and progesterone inhibit follicle formation and acquisition by newly formed follicles of the capacity to activate. Meiotic arrest of the oocyte in the diplotene stage of first prophase does not occur until after follicle formation and is correlated with acquisition of the capacity to activate. This may explain the gap between follicle formation and appearance of the first activated follicles. Once capacity to activate has been acquired, it seems likely that activation in vivo is controlled by the balance between stimulators and inhibitors of activation. Insulin and kit ligand stimulate and anti-Müllerian hormone (AMH) inhibits activation in vitro. Few bovine follicles transition from the primary to the secondary stage in vitro, but this transition is increased by medium supplements, testosterone and vascular endothelial growth factor (VEGF).

Additional keywords: follicular development, ovary.


References

Acosta, T. J., Hayashi, K. G., Matsui, M., and Miyamoto, A. (2005). Changes in follicular vascularity during the first follicular wave in lactating cows. J. Reprod. Dev. 51, 273–280.
Changes in follicular vascularity during the first follicular wave in lactating cows.Crossref | GoogleScholarGoogle Scholar | 15699584PubMed |

Baker, T. G., and Franchi, L. L. (1967). The fine structure of chromosomes in bovine primordial oocytes. J. Reprod. Fertil. 14, 511–513.
The fine structure of chromosomes in bovine primordial oocytes.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaF1c%2FptVCrsw%3D%3D&md5=fa6f6e8cfa8a4d4a9af274abea8579d6CAS | 6071015PubMed |

Cecconi, S., Barboni, B., Coccia, M., and Mattioli, M. (1999). In vitro development of sheep preantral follicles. Biol. Reprod. 60, 594–601.
In vitro development of sheep preantral follicles.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXhsFekt7g%3D&md5=5888c8d6bfcf64f538b72e02ac25b197CAS | 10026104PubMed |

Chen, Y., Jefferson, W. N., Newbold, R. R., Padilla-Banks, E., and Pepling, M. E. (2007). Estradiol, progesterone, and genistein inhibit oocyte nest breakdown and primordial follicle assembly in the neonatal mouse ovary in vitro and in vivo. Endocrinology 148, 3580–3590.
Estradiol, progesterone, and genistein inhibit oocyte nest breakdown and primordial follicle assembly in the neonatal mouse ovary in vitro and in vivo.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXot1OisLg%3D&md5=9e2d52d3174994a8baafd7820ea4f99aCAS | 17446182PubMed |

Cushman, R. A., Wahl, C. M., and Fortune, J. E. (2002). Bovine ovarian cortical pieces grafted to chick embryonic membranes: a model for studies on the activation of primordial follicles. Hum. Reprod. 17, 48–54.
Bovine ovarian cortical pieces grafted to chick embryonic membranes: a model for studies on the activation of primordial follicles.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD38%2FksFegsQ%3D%3D&md5=41a04ccfe9ff0258752869adc9a0b327CAS | 11756361PubMed |

Dominguez, M. M., Liptrap, R. M., and Basrur, P. K. (1988). Steroidogenesis in fetal bovine gonads. Can. J. Vet. Res. 52, 401–406.
| 1:CAS:528:DyaL1MXhvVKntg%3D%3D&md5=08050869108ea289c582b44c3ad5f907CAS | 3196968PubMed |

Durlinger, A. L. L., Kramer, P., Karels, B., de Jong, F. H., Uilenbroek, J. T. J., Grootegoed, J. A., and Themmen, A. P. N. (1999). Control of primordial follicle recruitment by anti-Müllerian hormone in the mouse ovary. Endocrinology 140, 5789–5796.
Control of primordial follicle recruitment by anti-Müllerian hormone in the mouse ovary.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXns12htLc%3D&md5=2a5e47ea29cc781241ba9de58057318aCAS | 10579345PubMed |

Eppig, J. J., and O’Brien, M. J. (1996). Development in vitro of mouse oocytes from primordial follicles. Biol. Reprod. 54, 197–207.
Development in vitro of mouse oocytes from primordial follicles.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXhtVSisLjO&md5=f1a9ca8e9aedbef3dd012df2c0259a2aCAS | 8838017PubMed |

Eppig, J. J., and Wigglesworth, K. (1995). Factors affecting the developmental competence of mouse oocytes grown in vitro: oxygen concentration. Mol. Reprod. Dev. 42, 447–456.
Factors affecting the developmental competence of mouse oocytes grown in vitro: oxygen concentration.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXpvVGisbw%3D&md5=36ee61baca1818d840e40c0a74a5b216CAS | 8607975PubMed |

Erickson, B. H. (1966). Development and radio-response of the prenatal bovine ovary. J. Reprod. Fertil. 11, 97–105.
Development and radio-response of the prenatal bovine ovary.Crossref | GoogleScholarGoogle Scholar |

Fortune, J. E., Kito, S., and Byrd, D. D. (1999). Activation of primordial follicles in vitro. J. Reprod. Fertil. Suppl. 54, 439–448.
| 1:STN:280:DC%2BD3c7lslalsQ%3D%3D&md5=d7a0133c4b37e7020081da2fe1be3b3fCAS | 10692874PubMed |

Fortune, J. E., Cushman, R. A., Wahl, C. M., and Kito, S. (2000). The primordial to primary follicle transition. Mol. Cell. Endocrinol. 163, 53–60.
The primordial to primary follicle transition.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXlvV2msrg%3D&md5=0019dde2cd4cb5254bd166d53ba714e5CAS | 10963874PubMed |

Garverick, H. A., Juengel, J. L., Smith, P., Heath, D. A., Burkhart, M. N., Perry, G. A., Smith, M. F., and McNatty, K. P. (2010). Development of the ovary and ontogeny of mRNA and protein for P450 aromatase (arom) and estrogen receptors (ER) alpha and beta during early fetal life in cattle. Anim. Reprod. Sci. 117, 24–33.
Development of the ovary and ontogeny of mRNA and protein for P450 aromatase (arom) and estrogen receptors (ER) alpha and beta during early fetal life in cattle.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhtlyjt7jP&md5=1ec08dfeded35ffd4d2e60904686fe25CAS | 19501990PubMed |

Gigli, I., Cushman, R. A., Wahl, C. M., and Fortune, J. E. (2005). Evidence for a role for anti-Müllerian hormone in the suppression of follicle activation in mouse ovaries and bovine ovarian cortex grafted beneath the chick chorioallantoic membrane. Mol. Reprod. Dev. 71, 480–488.
Evidence for a role for anti-Müllerian hormone in the suppression of follicle activation in mouse ovaries and bovine ovarian cortex grafted beneath the chick chorioallantoic membrane.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXlvFSltbg%3D&md5=5f31da8f8c8d39cec641f09a21c82380CAS | 15895366PubMed |

Gigli, I., Byrd, D. D., and Fortune, J. E. (2006). Effects of oxygen tension and supplements to the culture medium on activation and development of bovine follicles in vitro. Theriogenology 66, 344–353.
Effects of oxygen tension and supplements to the culture medium on activation and development of bovine follicles in vitro.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xmt1Gksbk%3D&md5=594a18430cf784cb067cdf548f2819ffCAS | 16442155PubMed |

Jefferson, W., Newbold, R., Padilla-Banks, E., and Pepling, M. (2006). Neonatal genistein treatment alters ovarian differentiation in the mouse: inhibition of oocyte nest breakdown and increased oocyte survival. Biol. Reprod. 74, 161–168.
Neonatal genistein treatment alters ovarian differentiation in the mouse: inhibition of oocyte nest breakdown and increased oocyte survival.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXhtlCjsrfM&md5=11b5635fec700ff658eec249d4b787beCAS | 16192398PubMed |

Kezele, P., and Skinner, M. K. (2003). Regulation of ovarian primordial follicle assembly and development by estrogen and progesterone: endocrine model of follicle assembly. Endocrinology 144, 3329–3337.
Regulation of ovarian primordial follicle assembly and development by estrogen and progesterone: endocrine model of follicle assembly.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXlslGjsLg%3D&md5=c742af3b41ef17951d87392f747cd2d6CAS | 12865310PubMed |

Koos, R. D., and Feiertag, M. A. (1989). The effect of reduced oxygen tension on progesterone accumulation in rat granulosa cell cultures. Steroids 54, 553–562.
The effect of reduced oxygen tension on progesterone accumulation in rat granulosa cell cultures.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3cXhs1Cmtg%3D%3D&md5=9b35e8e487933cacb981cd061a2170eaCAS | 2515620PubMed |

Manova, K., Huang, E. J., Angeles, M., De Leon, V., Sanchez, S., Pronovost, S. M., Besmer, P., and Bachvarova, R. F. (1993). The expression pattern of the c-kit ligand in gonads of mice supports a role for the c-kit receptor in oocyte growth and in proliferation of spermatogonia. Dev. Biol. 157, 85–99.
The expression pattern of the c-kit ligand in gonads of mice supports a role for the c-kit receptor in oocyte growth and in proliferation of spermatogonia.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3sXksVWktr0%3D&md5=e9bbdc71e06ef6cb9f47468adb73e2d7CAS | 7683286PubMed |

Mayerhofer, A., Dissen, G. A., Costa, M. E., and Ojeda, S. R. (1997). A role for neurotransmitters in early follicular development: induction of functional follicle-stimulating hormone receptors in newly formed follicles of the rat ovary. Endocrinology 138, 3320–3329.
A role for neurotransmitters in early follicular development: induction of functional follicle-stimulating hormone receptors in newly formed follicles of the rat ovary.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXkslShurw%3D&md5=12f9bdf33d91cb21fafe1e6ee1df96c2CAS | 9231784PubMed |

McNatty, K. P., Smith, P., Hudson, N. L., Heath, D. A., Tisdall, D. J., O, W. S., and Braw-Tal, R. (1995). Development of the sheep ovary during fetal and early neonatal life and the effect of fecundity genes. J. Reprod. Fertil. Suppl. 49, 123–135.
| 1:STN:280:DyaK2MzkvV2qug%3D%3D&md5=bab125a8f3da5051d4c45ba42423db46CAS | 7623307PubMed |

Motro, B., and Bernstein, A. (1993). Dynamic changes in ovarian c-kit and Steel expression during the estrous reproductive cycle. Dev. Dyn. 197, 69–79.
| 1:STN:280:DyaK2c%2FgtlCmug%3D%3D&md5=010cec45cdbb76960ed9110bcb510811CAS | 7691275PubMed |

Murray, A. A., Gosden, R. G., Allison, V., and Spears, N. (1998). Effect of androgens on the development of mouse follicles growing in vitro. J. Reprod. Fertil. 113, 27–33.
Effect of androgens on the development of mouse follicles growing in vitro.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXlsVSgtb8%3D&md5=4c0d8904159071c251da1c103eb90b3bCAS | 9713373PubMed |

Nilsson, E. E., and Skinner, M. K. (2009). Progesterone regulation of primordial follicle assembly in bovine fetal ovaries. Mol. Cell. Endocrinol. 313, 9–16.
Progesterone regulation of primordial follicle assembly in bovine fetal ovaries.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXht1WqurvL&md5=6d7c62ba1d06e155ee92b75ed27b900cCAS | 19747959PubMed |

Nilsson, E. E., Stanfield, J., and Skinner, M. K. (2006). Interactions between progesterone and tumor necrosis factor-alpha in the regulation of primordial follicle assembly. Reproduction 132, 877–886.
Interactions between progesterone and tumor necrosis factor-alpha in the regulation of primordial follicle assembly.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXmsF2itA%3D%3D&md5=c9248031438a4f6902096e2213358eeaCAS | 17127748PubMed |

Packer, A. I., Hsu, Y. C., Besmer, P., and Bachvarova, R. F. (1994). The ligand of the c-kit receptor promotes oocyte growth. Dev. Biol. 161, 194–205.
The ligand of the c-kit receptor promotes oocyte growth.Crossref | GoogleScholarGoogle Scholar | 7507447PubMed |

Parrott, J. A., and Skinner, M. K. (1999). Kit-ligand/stem cell factor induces primordial follicle development and initiates folliculogenesis. Endocrinology 140, 4262–4271.
Kit-ligand/stem cell factor induces primordial follicle development and initiates folliculogenesis.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXlslSru7k%3D&md5=6b6884560e2ee4e92a6eb5db0d736867CAS | 10465300PubMed |

Parrott, J. A., and Skinner, M. K. (2000). Kit ligand actions on ovarian stromal cells: effects on theca cell recruitment and steroid production. Mol. Reprod. Dev. 55, 55–64.
Kit ligand actions on ovarian stromal cells: effects on theca cell recruitment and steroid production.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXnvFyntrs%3D&md5=cd17aae22744adf6005452c6a6e16373CAS | 10602274PubMed |

Plendl, J. (2000). Angiogenesis and vascular regression in the ovary. Anat. Histol. Embryol. 29, 257–266.
Angiogenesis and vascular regression in the ovary.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3M7gt1enuw%3D%3D&md5=d27c03af6c938f7bc1a8697106bcb51dCAS | 11103513PubMed |

Quirke, L. D., Juengel, J. L., Tisdall, D. J., Lun, S., Heath, D. A., and McNatty, K. P. (2001). Ontogeny of steroidogenesis in the fetal sheep gonad. Biol. Reprod. 65, 216–228.
Ontogeny of steroidogenesis in the fetal sheep gonad.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXkslWhtbY%3D&md5=6f0fdc05d8af94fe5683b88b77b6f557CAS | 11420243PubMed |

Qvist, R., Blackwell, L. F., Bourne, H., and Brown, J. B. (1990). Development of mouse ovarian follicles from primary to preovulatory stages in vitro. J. Reprod. Fertil. 89, 169–180.
Development of mouse ovarian follicles from primary to preovulatory stages in vitro.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3cXktlCqtr4%3D&md5=94fdab0d8604a818e05ee667318301e4CAS | 2115582PubMed |

Reynaud, K., Cortvrindt, R., Smitz, J., Bernex, F., Panthier, J. J., and Driancourt, M. A. (2001). Alterations in ovarian function of mice with reduced amounts of KIT receptor. Reproduction 121, 229–237.
Alterations in ovarian function of mice with reduced amounts of KIT receptor.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXhslSisLc%3D&md5=20bfc0711097a6565522762928bb0684CAS | 11226047PubMed |

Rüsse, I. (1983). Oogenesis in cattle and sheep. Bibl. Anat. 24, 77–92.
| 6847603PubMed |

Shemesh, M., Allenberg, M., Milaguir, F., Ayalon, N., and Hansel, W. (1978). Hormone secretion by cultured bovine pre- and postimplantation gonads. Biol. Reprod. 19, 761–767.
Hormone secretion by cultured bovine pre- and postimplantation gonads.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaE1MXosValsg%3D%3D&md5=376bdb498cbe53b976b54b6d8816d4bbCAS | 581745PubMed |

Skinner, M. K. (2005). Regulation of primordial follicle assembly and development. Hum. Reprod. Update 11, 461–471.
Regulation of primordial follicle assembly and development.Crossref | GoogleScholarGoogle Scholar | 16006439PubMed |

Smitz, J., Cortvrindt, R., and Van Steirteghem, A. C. (1996). Normal oxygen atmosphere is essential for the solitary long-term culture of early preantral mouse follicles. Mol. Reprod. Dev. 45, 466–475.
Normal oxygen atmosphere is essential for the solitary long-term culture of early preantral mouse follicles.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XnsVWgs7g%3D&md5=f006bccb08091b3de249230e9b8501bfCAS | 8956285PubMed |

Tanaka, Y., Nakada, K., Moriyoshi, M., and Sawamukai, Y. (2001). Appearance and number of follicles and change in the concentration of serum FSH in female bovine fetuses. Reproduction 121, 777–782.
Appearance and number of follicles and change in the concentration of serum FSH in female bovine fetuses.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXktVait70%3D&md5=45e2fccbd5093b3652aa23e039018905CAS | 11427166PubMed |

van Wagenen, G., and Simpson, M. E. (1965). ‘Embryology of the Ovary and Testis. Homo sapiens and Macaca mulatta.’ (Yale University Press: New Haven, CT.)

Vendola, K. A., Zhou, J., Adesanya, O. O., Weil, S. J., and Bondy, C. A. (1998). Androgens stimulate early stages of follicular growth in the primate ovary. J. Clin. Invest. 101, 2622–2629.
Androgens stimulate early stages of follicular growth in the primate ovary.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXktVSitbw%3D&md5=98dcdc1c31fcaabd422cc704b25e6563CAS | 9637695PubMed |

Vendola, K. A., Zhou, J., Wang, J., Famuyiwa, O. A., Bievre, M., and Bondy, C. A. (1999). Androgens promote oocyte insulin-like growth factor I expression and initiation of follicle development in the primate ovary. Biol. Reprod. 61, 353–357.
Androgens promote oocyte insulin-like growth factor I expression and initiation of follicle development in the primate ovary.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXkslKqsbo%3D&md5=cc94c203ecf3859e3a012f2ec1256902CAS | 10411511PubMed |

Wandji, S.-A., Srsen, V., Voss, A. K., Eppig, J. J., and Fortune, J. E. (1996). Initiation in vitro of growth of bovine primordial follicles. Biol. Reprod. 55, 942–948.
Initiation in vitro of growth of bovine primordial follicles.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28Xmtlamsr4%3D&md5=a5084901ae4ac49c422880053443477bCAS | 8902203PubMed |

Wandji, S.-A., Srsen, V., Nathanielsz, P. W., Eppig, J. J., and Fortune, J. E. (1997). Initiation of growth of baboon primordial follicles in vitro. Hum. Reprod. 12, 1993–2001.
Initiation of growth of baboon primordial follicles in vitro.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK1c%2FivVenuw%3D%3D&md5=b4e3e81f070ea779081f4d73d85a6064CAS | 9363719PubMed |

Wang, H., Andoh, K., Hagiwara, H., Xiaowei, L., Kikuchi, N., Abe, Y., Yamada, K., Fatima, R., and Mizunuma, H. (2001). Effect of adrenal and ovarian androgens on type 4 follicles unresponsive to FSH in immature mice. Endocrinology 142, 4930–4936.
Effect of adrenal and ovarian androgens on type 4 follicles unresponsive to FSH in immature mice.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXnslGqu7s%3D&md5=47ffc75ac10cb2d39afa34154e6c4f5aCAS | 11606461PubMed |

Yang, M. Y., and Fortune, J. E. (2006). Testosterone stimulates the primary to secondary follicle transition in bovine follicles in vitro. Biol. Reprod. 75, 924–932.
Testosterone stimulates the primary to secondary follicle transition in bovine follicles in vitro.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xht1yjtr7P&md5=179f0ba28028d02c164e755565b21779CAS | 16943368PubMed |

Yang, M. Y., and Fortune, J. E. (2007). Vascular endothelial growth factor stimulates the primary to secondary follicle transition in bovine follicles in vitro. Mol. Reprod. Dev. 74, 1095–1104.
Vascular endothelial growth factor stimulates the primary to secondary follicle transition in bovine follicles in vitro.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXpt1alsL8%3D&md5=b07924eeb35e27b70327ff1a4084bf1eCAS | 17290425PubMed |

Yang, M. Y., and Fortune, J. E. (2008). The capacity of primordial follicles in fetal bovine ovaries to initiate growth in vitro develops during mid-gestation and is associated with meiotic arrest of oocytes. Biol. Reprod. 78, 1153–1161.
The capacity of primordial follicles in fetal bovine ovaries to initiate growth in vitro develops during mid-gestation and is associated with meiotic arrest of oocytes.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXmsVWkur8%3D&md5=6b4df08a2875c308636d7a260859020dCAS | 18305225PubMed |

Yoshida, H., Takakura, N., Kataoka, H., Kunisada, T., Okamura, H., and Nishikawa, S.-I. (1997). Stepwise requirement of c-kit tyrosine kinase in mouse ovarian follicle development. Dev. Biol. 184, 122–137.
Stepwise requirement of c-kit tyrosine kinase in mouse ovarian follicle development.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXivV2it7Y%3D&md5=e40ca58d4ed66393c6383af20eae146bCAS | 9142989PubMed |

Zeleznik, A. J., Schuler, H. M., and Reichert, L. E., Jr (1981). Gonadotropin-binding sites in the rhesus monkey ovary: role of the vasculature in the selective distribution of human chorionic gonadotropin to the preovulatory follicle. Endocrinology 109, 356–362.
Gonadotropin-binding sites in the rhesus monkey ovary: role of the vasculature in the selective distribution of human chorionic gonadotropin to the preovulatory follicle.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL3MXkvFCkt7k%3D&md5=f55e7efdca87cd80380180ae3cf6f264CAS | 6265188PubMed |