Inhibitors of lipoxygenase increase the ovulation rate in the in-vitro perfused luteinizing hormone-stimulated rabbit ovary

Inhibition of ovulation by a lipoxygenase inhibitor involves reduced cyclooxygenase-2 expression and prostaglandin E2 production in gonadotropin-primed immature rats

Potential roles of cyclooxygenase (COX) pathway of arachidonic acid (AA) metabolism are established in a murine model of induced ovulation. Pharmacological inhibition of an alternative lipoxygenase (LOX) pathway has been shown to cause defective ovulation, but the mechanism is still undefined. This study investigated the effects of two LOX inhibitors and their time dependency on ovulation and COX activity in gonadotropins (eCG and human chorionic gonadotropin (hCG))-primed immature rats. Intra-ovarian bursal treatment with a general LOX inhibitor nordihydroguaiaretic acid (NDGA) at 0 h post-hCG (hCG0h) dose dependently inhibited ovulation rate. The drug was still but less effective when treated at hCG6h. A more specific inhibitor, 3,4-dihydroxyphenyl ethanol (DPE) was also inhibitory when treated at hCG0h but not at hCG6h. Interestingly, treatment with DPE at hCG0h resulted in attenuated expression of immunoreactive PTGS2 in granulosa layers and concomitant decrease in ovarian prostaglandin E(2) (PGE(2)) content at hCG8h. NDGA treatment reduced immunoreactive PTGS2. Ovulatory impairment by both inhibitors was prevented by systemic administration of PGE(2) at hCG6h. Immunohistochemistry revealed the expression of ALOX5 and ALOX12 in both thecal and granulosa layers of preovulatory follicles and, notably, the augmented immunoreactivities during 8 h after hCG treatment. Our results indicate the probable presence of multiple LOX isoforms and that specific inhibition of LOX at an early stage of hCG-signaling led to reduced PTGS2 activity and thus defective ovulation. They reveal a probable relationship between two pathways of AA metabolism and account at least partly for the mechanism by which the LOX inhibitor causes impaired ovulation.

Effects of salicylhydroxamic acid on the proliferation of Atriplex and murine neuroblastoma cells, and on Drosophila egg laying and development

Salicylhydroxamic acid (SHAM) inhibits the proliferation of cultured plant (Atriplex halimus) and murine neuroblastoma cells with IC50 of 90 and 250 microM, respectively. After 2 h of application, SHAM induces an acceleration of the neuroblastoma cell cycle from G1/S to G2 phases and, after 6 h, it induces an accumulation of the cells in S phase and a cell swelling. Up to 300 microM, SHAM is not cytotoxic and does not induce electrophysiological differentiation of neuroblastoma cells. When Drosophila females are grown in media containing 0.6-1.25 mM SHAM, the rate and number of laid eggs are increased. Furthermore, SHAM stimulates the different development stages from embryo to adult. A general interpretation of the effects of SHAM on cell proliferation and differentiation is proposed.

Ovulation as a tissue remodelling process. Proteolysis and cumulus expansion

Ovulation, recurring every midcycle of the mammalian female and triggered by a surge of luteinizing hormone (LH) released from the pituitary, is an essential prerequisite for fertilization and subsequent embryonic development. Here we shall describe two of the biological components of the ovulatory response, cumulus expansion (frequently denoted as cumulus maturation) and the rupture of follicular wall, both crucial for the release of a fertilizable ovum. The role of a proteolytic cascade and its regulation by eicosanoids will be emphasized in relation to follicle rupture. The new data implicating cumulus maturation as an essential step for the release of the ovum and the apparent mediatory role of interleukin-1 in this process will be presented. LH/hCG stimulates, in the preovulatory follicles, a cascade of proteolytic enzymes, including plasminogen activator (PA), plasmin and matrix metalloproteinase 1 (MMP-1). These enzymes bring about the degradation of perifollicular matrix and, most notably, the decomposition of the meshwork of collagen fibers which provides the strength to follicular wall. Furthermore, pharmacological blockage of any of these enzymes resulted in inhibition of follicle rupture. LH/hCG stimulates, in addition, an increase in ovarian production of eicosanoids. These include prostaglandins, obtained from arachidonic acid via the cyclooxygenase pathway and leukotrienes, the products of lipoxygenase. Previous studies from our and other laboratories have demonstrated the ability of inhibitors of cyclooxygenase and of lipoxygenases to suppress ovulation in several mammalian species. MK-886, which inhibits the translocation of 5-lipoxygenase (5-LO) from the cytosol and its binding to the membranal 5-LO activating enzyme, suppressed dose-dependently follicular rupture from the treated ovary. Zymographic analysis of ovarian extracts from PMSG/hCG-stimulated rats revealed a band of collagenolytic activity at 52kD, corresponding to human MMP-1 and at 72kD, corresponding to human MMP-2. Both activities were markedly stimulated by administration of hCG and were significantly inhibited by indomethacin, NDGA or MK-886. Thus, eicosanoids seem to mediate LH stimulation of follicular collagenase. Interleukin-1 (IL-1) has been recently implicated in ovulation. The ability of an IL-1 receptor antagonist (ra) to block ovulation in vivo and in vitro has been demonstrated recently. Morphological examination of the ovulatory follicles failing to ovulate suggests that this effect is exerted by inhibiting cumulus oophorus expansion and detachment from mural granulosa cells. In vitro, IL-1ra attenuated the action of hCG and FSH on cumulus expansion and follicular hyaluronic acid synthesis. Thus, IL-1 seems to mediate and/or facilitate gonadotropin action on cumulus expansion, and hence on ovulation.

Prostaglandins in the ovary and fallopian tube

More than 20 years following the recognition of a possible role for eicosanoids in ovarian function a physiological role for prostaglandins and/or leukotrienes in human ovulation, corpus luteum function and tubal motility remains to be demonstrated. With respect to ovarian function, the well-characterized preovulatory rise in eicosanoid production in animal species and humans, in conjunction with the large body of experimental evidence employing inhibitors of prostaglandin synthesis and replacement of individual prostaglandins, has provided strong evidence for a role in follicular rupture independent of other LH-mediated ovulatory events. The possible mechanism of prostaglandin-induced follicle rupture may involve stimulation of proteolytic activity via substances such as plasmin and PA; however, this is controversial. A role for prostaglandins in ovarian luteal function is well established in laboratory animals and large ruminant species, where PGF2 alpha derived from the uterus has been demonstrated to be the luteolytic factor. In humans, luteal function may be influenced by local intraovarian eicosanoid production, which has been suggested to involve the paracrine interaction of local ovarian hormones such as oxytocin, noradrenaline, insulin and IGFs, to name but a few. Several lines of evidence have also implicated prostaglandins as an aetiological factor in ovarian pathological states such as seen in the OHSS. However, the bulk of clinical experimental evidence to date has failed to support this contention. Prostaglandin production has likewise been well characterized in the fallopian tube in both humans and animal species. Whereas a role for prostaglandins in tubal transport has been demonstrated with animal species such as the rabbit, several studies have failed to define a similar function in humans. More recently, direct injections of prostaglandin analogues into the fallopian tube and the corpus luteum have been shown to be efficacious as a treatment for ectopic pregnancy. Whether the primary mechanism of action involves effects on tubal musculature or corpus luteum function, or is simply a local vascular effect, remains to be demonstrated. Therefore, although the physiological role for eicosanoids in ovarian and tubal function remains unclear, particularly in the human, an increasing body of recent evidence has suggested an important paracrine function for this class of cellular mediators whose interaction with other more recently characterized local ovarian factors has only begun to be recognized.