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Inhibition of ovulation by tyrosine kinase inhibitors in the in vitro perfused rat ovary

Protein tyrosine kinase activity, leading to tyrosine phosphorylation of the intracellular domains of receptors or non-receptor proteins, is an important feature of downstream signalling after receptor binding of a variety factors, such as growth factors and cytokines. Since several members of these classes of paracrine–autocrine mediator may be involved in the intraovarian events of ovulation, the present study was designed to evaluate the effect of protein tyrosine kinase inhibition on the in vitro perfused rat ovary. Immature rats were primed with 20 iu pregnant mares' serum gonadotrophin 48 h before surgical isolation of the right ovary with connecting vasculature. The ovary was placed in a perfusion system for either 10 h, to examine ovarian concentrations of the etablished ovulatory mediators plasminogen activator, prostaglandins E₂ and F₂, or for 20 h, enabling a complete ovulatory process to occur in vitro. Ovulation was induced by ovine LH (0.2 µg ml^–1) in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.2 mmol l^–1) and the effects of two different protein tyrosine kinase inhibitors, genistein and tyrphostin A25, were studied. Unstimulated control ovaries did not ovulate and showed low secretion of progesterone and oestradiol. Addition of LH + 3-isobutyl-1-methylxanthine resulted in a marked stimulation of steroid release, and ovulations occurred in all ovaries (9.0 ± 0.9; mean ± SEM). The protein tyrosine kinase inhibitors, genistein and tyrphostin A25, significantly inhibited ovulation at the higher concentrations tested (3.0 ±0.3 at 100 µmol genistein l^–1; 5.8 ± 1.0 at 500 µmol tyrphostin A25 l^–1) but no effect was seen at lower concentrations. The presence of genistein and tyrphostin A25 at any concentration used did not significantly decrease the LH + 3-isobutyl-1-methylxanthine-induced progesterone or oestradiol concentrations. The intraovarian concentrations of plasminogen activator activity, and prostaglandin E₂ and F₂ were not altered by the presence genistein (100 µmol l^–1). In conclusion, the results of the present study indicate that protein tyrosine kinase signalling pathways are integral parts of the mammalian ovulatory process but do not involve actions on the synthesis of steroids, plasminogen activator or prostaglandins.

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