Pure preovulatory follicular fluid promotes in vitro maturation of in vivo aspirated equine oocytes.

In the mare, rates of fertilization and development are low in oocytes matured in vitro, and a closer imitation of in vivo conditions during oocyte maturation might be beneficial. The aims of the present study were, therefore, to investigate whether (1) equine oocytes can be matured in vitro in pure equine preovulatory follicular fluid, (2) priming of the follicular fluid donor with crude equine gonadotrophins (CEG) before aspiration of preovulatory follicular fluid promotes the in vitro maturation rate, (3) the in vitro maturation rate differs between oocytes aspirated during estrus and those aspirated again 8 days after the initial follicular aspiration, and (4) high follicular concentrations of meiosis activating sterols (MAS) are beneficial for in vitro maturation of equine oocytes. During estrus, 19 pony mares were treated with 25 mg CEG.

Tissue-specific transcriptional regulation of the cholesterol biosynthetic pathway leads to accumulation of testis meiosis-activating sterol (T-MAS).

Lanosterol 14alpha-demethylase (CYP51) produces follicular fluid meiosis-activating sterol (FF-MAS), which is converted further to testis meiosis-activating sterol (T-MAS). MAS are intermediates in the cholesterol biosynthetic pathway, with the ability to trigger resumption of oocyte meiosis in vitro. In contrast to the liver, where pre- and post-MAS genes are upregulated coordinately at the level of transcription by a cholesterol feedback mechanism through sterol regulatory element-binding proteins (SREBP), regulation differs in the testis.

Gonadotropin-induced accumulation of 4,4-dimethylsterols in mouse ovaries and its temporal relation to meiosis.

The resumption of oocyte meiosis is triggered by a number of 4,4-dimethylsterols termed meiosis-activating sterols (MAS). The levels of meiosis active (follicular fluid [FF]-MAS and bull testes [T]-MAS) and inactive (lanosterol) 4,4-dimethylsterols, free cholesterol, and progesterone were determined in gonadotropin-primed prepubertal mouse ovaries in vivo by high-performance liquid chromatography. Ovaries responded to an ovulatory stimulation by increasing their content of 4,4-dimethylsterols but not of free cholesterol.

Content of meiosis activating sterols in equine follicular fluids: correlation to follicular size and dominance.

Meiosis activating sterols (MAS) are pre-cholesterol sterols that can be isolated from follicular fluid (FF-MAS) or testes (T-MAS). Meiosis activating sterols trigger the resumption of meiosis in cultured meiotically competent oocytes. In the present work MAS, cholesterol and progesterone were assayed by HPLC in follicular fluids collected from pony mares at fixed days after the last ovulation.

Testicular concentration of meiosis-activating sterol is associated with normal testicular descent.

In the cryptorchid stallion, spermatogenesis is arrested at various levels before the completion of meiosis. In men, infantile cryptorchidism is also often associated with oligo- and azoospermia during adulthood. An impairment of spermatogenesis might be reflected in the level of locally produced factors.