The effect of platelet activating factor on ovulation

Analysis of ether glycerophosphocholines at the level of CC locations from human plasma

Near-complete structural characterization is achieved for ether PCs by coupling offline Paternò–Büchi derivatization with MS/MS.

Platelet-activating factor synthesis and receptor-mediated signaling are downregulated in ovine newborn lungs: relevance in postnatal pulmonary adaptation and persistent pulmonary hypertension of the newborn

Platelet-activating factor (PAF) is a phospholipid with a wide range of biological activities. We studied PAF metabolism and PAF receptor (PAFR) signaling in perinatal ovine lungs to understand PAF's role in transition of the perinatal pulmonary hemodynamics and pathophysiology of persistent pulmonary hypertension of the newborn. We hypothesized that downregulation of PAF synthesis with upregulation of PAF catabolism by acetylhydrolase (PAF-Ah) in the newborn lung is needed for fetus-to-newborn pulmonary adaptation. Studies were conducted on fetal and newborn lamb pulmonary arteries (PA), veins (PV) and smooth muscle cells (SMC). PAF metabolism, PAFR binding and cell proliferation were studied by cell culture; gene expression was studied by qPCR. Fetal lungs synthesized 60% more PAF than newborn lungs. Compared with the fetal PVs and SMCs, PAF-Ah activity in newborn was 40-60% greater. PAF-Ah mRNA expression in newborn vessels was different from the expression by fetal PA. PAF-Ah gene clone activity confirmed deletion of hypoxia-sensitive site. PAFR mRNA expression by the PVs and SMC-PV of the fetus and newborn was greater than by corresponding PAs and SMC-PA. Q-PCR study of PAFR expression by the SMC-PV of both groups was greater than SMC-PA. Fetal SMCs bound more PAF than the newborn SMCs. PAFR antagonist, CV-3988, inhibited PAFR binding and DNA synthesis by the fetal SMCs, but augmented binding and DNA synthesis by newborn cells. We show different PAF-PAFR mediated effects in perinatal lungs, suggesting both transcriptional and translational regulation of PAF-Ah and PAFR expression in the perinatal lamb lungs. These indicate that the downregulation of PAF-mediated effects postnatally protects against persistent pulmonary hypertension of the newborn.

Intravenous infusion of PAF affects ovulation, fertilization and preimplantation embryonic development in NZB x NZW F1 hybrid mice

Platelet Activating Factor (PAF) is a bioactive phospholipid, which exhibits a variety of biological activities and plays a significant role in all aspects of reproduction. In this work, a single intravenous injection of various concentrations of PAF shortly after Human Chorionic Gonadotropin (HCG) administration as well as 24 and 48 h before HCG administration was studied in NZB x NZW F1 hybrid mice. Optimum results were observed when PAF was injected just after the administration of HCG. In this protocol, the concentrations of PAF exhibited bell-shaped response to every stage of development. Any concentration of PAF between 5.5 x 10(-11) and 5.5 x 10(-15)g/g b.w., caused an improved ovulation rate, an increased fertilization rate, an increased rate of cell cycle and an enhanced hatching blastocyst rate (P<0.05 for all stages). Injection of lyso-PAF had no effect in any stage. Our data show that the effect of PAF on early stages of embryo development in vitro is dependent on its way of administration, on the concentrations used as well as on the time PAF is injected.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

Essential role of platelet-activating factor in male reproduction: a review

The use of pharmacological adjuvants to enhance sperm function is a real possibility and a very attractive proposition. However, the role of such adjuvants must be well defined to maximize therapeutic outcome for specific patient populations. Platelet-activating factor (PAF) is a potent signalling phospholipid that has been implicated in a number of biological activities. In the field of reproductive biology, PAF has been shown to have an important role in ovulation, sperm function, embryo implantation, fetal lung maturation, and initiation and maintenance of parturition. Although the exact mechanisms are not clear, it has been demonstrated in several species that PAF can influence sperm function by affecting the motility, capacitation, acrosome reaction and fertility of spermatozoa. The reproductive significance of PAF activity in spermatozoa and fertilization and its role in the establishment of pregnancy requires further study. Understanding the role of PAF in a reproductive process, such as in intrauterine insemination, could eventually lead researchers to explore its role in more complex reproductive technologies. This review summarizes the current research on the significant role of PAF in male mammalian reproductive functions, as well as its possible application in some assisted reproductive technologies.

Influence of the preimplantation embryo development (Ped) gene on embryonic platelet-activating factor (PAF) levels

PURPOSE

A major gene responsible for the control of preimplantation cleavage rate is the Ped gene, the product of which is the Qa-2 protein. Fast, but not slow developing mouse embryos express the Qa-2 protein. Platelet-activating factor (PAF) is a novel and potent signaling phospholipid that has unique pleiotropic properties in addition to platelet activation. PAF plays a significant role in virtually every reproductive event, including ovulation, fertilization, implantation, and parturition. The role of the Ped gene in PAF production by preimplantation embryos is yet to be established. The presence of this gene provides embryos with a reproductive advantage over those that are Ped negative, and may also serve as a regulator of PAF synthesis. The study hypothesis is that the amount of PAF produced is dependent upon the presence or absence of the Ped gene.

METHODS

B6.K1 (Ped negative) and B6.K2 (Ped positive) mouse embryo-conditioned culture media were assayed for PAF content by a PAF-specific radioimmunoassay.

RESULTS

There was a significant (p < 0.001) difference in blastocyst development rates between the Ped+ B6.K2 (61.0%) and the Ped- B6.K1 (25.3%) embryo culture groups. There was a significant difference (p < 0.05) in PAF production between the Ped+ B6.K2 (4.70+/-0.46 pmol per embryo) embryo culture group and the Ped- B6.K1 (10.02+/-3.49 pmol per embryo) embryo group. The B6.K1 (Ped-) embryo group produced >2x more PAF than did the B6.K2 (Ped+) group.

CONCLUSIONS

The Ped gene plays a role in PAF production and release in preimplantation stage embryos. The use of two mouse identical strains, except for the Ped gene, show that its presence is associated with an increase in developmental potential. Embryos where the Ped gene was absent produced significantly higher levels of PAF, which may aid in their survival.

Comparison of the coding sequence of the platelet-activating factor receptor gene in three species

The actions of platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) are mediated through the PAF receptor (PAFr), which is a member of G-protein coupled superfamily of receptors. Our laboratory has data showing PAF has a role(s) in reproduction in domestic animals. Porcine, bovine and caprine PAFr genes cloned in BAC vectors were sequenced. Each PAFr coding sequence (cds) in these three species is 1029 nucleotides long and contains no intervening sequences. The deduced amino acid sequences (AAS) appear to contain seven putative transmembrane domains with an extracellular N-terminus in each species. There is a common glycosylation site at the fourth asparagine residue of N-terminus. In the tail of each deduced amino acid sequence, five to six serines and five threonine residues could act as phosphorylation sites, which play an important role in rapid receptor desensitization. The degree of homology of the three species is from 89 to 96% in nucleotide sequences (NtS), and 87-96% in identities (I) and 94-97% in positives (P) in amino acid sequences (AAS). The degree of homology with human, guinea pig, mouse and rat is 84-87, 82-88 and 83-88% in NtS, 77-84 (I) or 85-90 (P), 77-84 (I) or 85-90 (P) and 75-83 (I) or 87-90% (P) in AAS for caprine, bovine and pig, respectively. Southern blotting results suggested that the PAFr gene exists as a single copy in the genome of pig.

Endocrine-regulated and protein kinase C-dependent generation of superoxide by rat preovulatory follicles

The ovulatory LH surge results in follicular inflammation with an increase in cytokines and PGs. Reactive oxygen species (ROS) are also produced during inflammatory processes. To study ROS generation during the ovulatory cascade, preovulatory follicles were dissected from immature female rats primed with PMSG. Follicles were isolated, and ROS generation was assessed by luminol-amplified chemiluminescence. Immature rat granulosa cells were also subjected to luminometry after isolation from immature rats treated with diethylstilbestrol. Phorbol ester-stimulated ROS generation by follicular cells was completely suppressed by superoxide dismutase and the NADPH/NADH oxidase inhibitor diphenylene iodonium bisulfate, whereas catalase was without effect. Fractionation of granulosa cells with an antibody against leukocyte common antigen-1 showed that leukocyte-enriched cells produced more than 95% of the superoxide measured. In vivo treatment with LH produced a 5-fold increase in phorbol-stimulated superoxide production by isolated follicles. This response was maximal within 4 h and was blocked by indomethacin. In vivo administration of PGE(2) and PGF(2alpha) did not reverse the blockade by indomethacin; however, isolated follicles incubated with PGE(2) produced a time-dependent increase in phorbol-stimulated superoxide generation. Thus, a superoxide generator is present in the preovulatory follicle that is leukocytic in origin, hormone regulated, and activated by a protein kinase C-dependent pathway. The regulated generation of superoxide by preovulatory follicles may indicate a role for ROS in the periovulatory period.

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.

Effects of platelet activating factor on mouse sperm function

Platelet activating factor (PAF) has been implicated in a variety of reproductive processes. This study was designed to investigate the effect of PAF and the specific PAF receptor antagonist, CV-3988, on capacitation and the acrosome reaction in mouse spermatozoa using an in vitro fertilization (IVF) system. When spermatozoa were preincubated for 30 min in medium containing PAF (10(-7) to 10(-11) M), a significant increase in the fertilization rate with both cumulus-free and zona-free oocytes was observed. In contrast, treatment of the spermatozoa with 10(-5) M CV-3988 caused a significant decrease in both sperm motility and fertilization rates with zona-intact and zona-free oocytes. This suppression was reversed by the addition of PAF. Furthermore, the acrosome reaction was enhanced by PAF treatment of spermatozoa in a dose-dependent manner. This stimulation of the acrosome reaction by PAF required the presence of calcium ions in the medium. While 10(-5) M CV-3988 inhibited the acrosome reaction, the inhibition was also reversed by the addition of PAF. These results suggest that PAF can stimulate not only the capacitation process but also the acrosome reaction, both of which are dependent on extracellular calcium.