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Biomedical subjects

C O'Neill

Publications and source records attributed to C O'Neill.

At least 127 records · Page 7Linked to original sources
PubMed1993

Production and secretion of progesterone in vitro and presence of platelet activating factor (PAF) in early pregnancy of the marsupial, Macropus eugenii.

The corpus luteum (CL) of the tammar is suppressed by lactation. Removal of the sucking pouch young induces reactivation of the CL which produces a peak in plasma progesterone concentration on Day 5, 6 or 7; reactivation of the embryo after diapause precedes by one day this transient peak of progesterone. This study examines progesterone production and secretion in vitro by the CL and the production of platelet activating factor (PAF) by the endometrium during this stage of pregnancy (Days 0 and 3-8). Blood samples were collected twice daily to determine for each animal (n = 28) at autopsy the relationship of PAF production to the day of the progesterone peak. Significant changes in basal plasma progesterone concentrations were used to define four groups according to the time the animals were killed: Group A, Day 0; Group B, other animals showing no significant change; Group C, peripheral progesterone concentration increasing; Group D, peripheral progesterone concentration decreasing after the peak. At autopsy on successive days, blood samples were taken from the heart, caudal vein and uterine branch of the ovarian vein, and CL and endometria were prepared for explant culture. Progesterone contents of pre- and post-incubation luteal tissues and of medium were determined at 4, 12 and 24 h to estimate production and secretion rates. The values for all progesterone parameters from animals in Group C were significantly higher than in the other groups. It is concluded that the progesterone peak results from a change in rate of production and secretion of progesterone by the CL, one day before the peak in peripheral plasma, and that this change could provide the first signal to the uterus. Endometrium was incubated for 24 h and the medium assayed for PAF. High concentrations of PAF were detected in half the animals in Groups B and C, that is, before or at the time progesterone was increasing. This is the first measurement of PAF in any marsupial and the first demonstration of the release of PAF by the endometrium. The detection of PAF provides a candidate for an endometrial signal that is responsive to the rising progesterone concentration in the utero-ovarian vein draining the CL-bearing ovary and that may stimulate reactivation of the blastocyst.

Animals↗
PubMed1993

Platelet activating factor (PAF) enhances mitosis in preimplantation mouse embryos.

Preimplantation mouse embryos were used to determine whether the reported significant increase in embryo metabolism and viability achieved through supplementation of the culture medium with the ether phospholipid 1-o-alkyl-2-acetyl-sn-glycero-3-phosphocoline (platelet activating factor, PAF) is attributable to an enhanced rate of mitosis. Blastocyst-stage embryos cultured in the presence of 0.186 to 18.6 microM exogenous PAF had a significantly (P < 0.01) higher mitotic index (the proportion of cells arrested in metaphase following incubation in colchicine) than those cultured without PAF. At the 8-cell stage, 29% more blastomeres were in metaphase in the PAF-treated group (P < 0.01) 8 h after the addition of colchicine, but by 16 h there was no difference between groups; thus, PAF increased the rate at which cells entered metaphase but did not increase the total number. The mitotic index showed a negative correlation with the number of cells within blastocysts. PAF had a significantly (P < 0.01) greater impact on the mitotic index of blastocysts with fewer cells. The action of PAF was specific, being completely blocked by the PAF-receptor antagonist WEB 2086 (33 microM). In the absence of exogenous PAF the mitotic index was lower with WEB 2086 than without, suggesting inhibition of the action of endogenous embryo-derived PAF. These results show that PAF stimulates the rates at which cells within the preimplantation mouse embryo enter metaphase in vitro and suggest that it would decrease their doubling time, perhaps accounting for the embryotrophic actions of PAF.

Animals↗
PubMed1993

Enterotoxigenic bacteria in the sudden infant death syndrome.

Faecal samples from 123 infants who died with sudden infant death syndrome (SIDS) and from a comparative group of 52 age-matched babies were analysed for toxigenic bacteria and their toxins. Serum samples from the SIDS infants were also analysed for these toxins. A significantly higher proportion of toxigenic bacteria and their toxins were found in faecal samples of SIDS babies than in samples from the comparative group. These toxins were also found in serum from the SIDS babies. Clostridium perfringens was found in 54 (45.4%) of 119 SIDS cases compared with 10 (19.6%) of 51 healthy babies (chi 2 = 10.1, p < 0.01); C. difficile in 33 (27.7%) of 119 SIDS cases compared with 8 (14.8%) of 54 healthy babies (chi 2 = 3.43ns, p < 0.1); Staphylococcus aureus in 12 (27.3%; 66.7% enterotoxigenic) of 44 SIDS cases compared with 12 (85.7%; non-enterotoxigenic) of 14 healthy babies (chi 2 = 14.9, p < 0.001); C. botulinum in 6 (5.0%) of 120 SIDS cases compared with 0 of 53 healthy babies (chi 2 = 2.74, p < 0.1). Campylobacter jejuni, Yersinia enterocolitica, Vibrio parahaemolyticus, salmonellae and Bacillus cereus were not detected. Heat-labile toxin, lethal to mice (HLML) was found in 32 (27.1%) of 118 SIDS faecal samples compared with 5 (10.6%) of 47 healthy babies (chi 2 = 5.24, p < 0.05); cytotoxins in 38 (30.9%) of 123 SIDS faecal samples compared with 0 of 21 of healthy babies (chi 2 = 8.8, p < 0.01) and 24 (27.6%) of 87 SIDS serum samples. C. perfringens enterotoxin was detected in 33 (34.4%) of 96 SIDS faecal extracts compared with 0 of 23 of healthy babies (chi 2 = 10.94, p < 0.001), and in 27 (24.5%) of 110 SIDS serum samples. C. perfringens alpha-toxin (presumptive) was detected in 14 (17.5%) of 80 SIDS faecal extracts compared with 0 of 17 from healthy babies (chi 2 = 3.5ns, p congruent to 0.05) and in 2 (2.3%) of 87 SIDS serum samples. C. difficile toxin was detected in four SIDS faecal samples and two serum samples. C. botulinum toxin was detected in only one of 120 SIDS faecal samples compared with none of 49 from healthy babies. Staphylococcal enterotoxins were detected in 8 (19.5%) of 41 SIDS faecal samples compared with 0 of 19 from healthy babies (chi 2 = 4.278, p < 0.05), and in 4 (10.8%) of 37 SIDS serum samples.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Biochemical pathology and treatment strategies in Alzheimer's disease: emphasis on the cholinergic system.

The neurochemical pathology of Alzheimer's disease (AD) has been consistently shown to involve cholinergic degeneration in the cerebral cortex. This together with evidence from experimental animal studies showing that cholinergic neurones play a role in learning and memory processes has formed the basis of the cholinergic hypothesis of Alzheimer's dementia and the major rationale for neurotransmitter replacement therapy of the disorder.

Acetylcholine↗
PubMed1993

Potential synergism between platelet-activating factor and alpha 1-recombinant interferon in promoting luteal maintenance in cyclic ewes.

In sheep, the presence of an embryo in utero on the 12th to 13th day after oestrus prevents luteolysis. These studies investigated whether platelet-activating factor (PAF) could exert an antiluteolytic function, either alone or in combination with interferon. The intrauterine administration of 250 micrograms PAF per horn per day, administered through indwelling cannulae into the uterus as injections twice a day (n = 12) or by continuous infusion (n = 4) failed to extend luteal function compared with controls (n = 8). When indwelling cannulae were used to administer (i) 125 micrograms PAF per uterine horn, as a bolus infusion twice a day (n = 5), (ii) continuous infusion of 500 micrograms bovine recombinant alpha 1-interferon each day (brIFN, n = 5), (iii) 125 micrograms PAF per horn twice a day, plus 500 micrograms brIFN per day (n = 8), or (iv) vehicle (n = 5), the luteal phase was significantly longer in co-infused (iii) than in control (iv) animals. These findings indicate that pharmacological doses of PAF may act synergistically with interferons to prevent luteolysis.

Animals↗
PubMed1993

Chloroplast transformation in plants: polyethylene glycol (PEG) treatment of protoplasts is an alternative to biolistic delivery systems.

Nicotiana plumbaginifolia protoplasts were directly transformed by PEG treatment with a cloned 16S rRNA gene isolated from a double antibiotic-resistant Nicotiana tabacum plastid mutant. Putative plastid transformants were selected in cell culture by their spectinomycin resistance and identified by their unselected streptomycin resistance. Alternatively, cell lines were selected in the presence of both antibiotics. The cell line (and its regenerated plants) selected solely for spectinomycin resistance demonstrated an extensive segregation of streptomycin resistance in subsequent tests, while the double-selected line showed stable resistance for both antibiotics. The resistance markers were inherited maternally. In the putative plastid transformants the origin of the resistance mutations was identified by the absence of an AatII site, missing in the donor N. tabacum plastid gene (spectinomycin resistance site) but present in that of wild-type N. plumbaginifolia, and a sequence analysis of the particular nucleotide changes in both resistance sites. Restriction enzyme analysis of total plastid DNA (ptDNA), and the recloning and full sequencing of the fragment introduced, investigated in one of the plastid transformants, showed no DNA rearrangements accompanied with the integration process. Sequence analysis indicated a targeted, homologous integration of the DNA fragment introduced but an unexpectedly complete homology of the parental ptDNA sequences in this region prevented the location of borders. Although the frequency of plastid transformant colonies (2 x 10(-5)) should still be improved, this method for stable chloroplast DNA transformation is comparable with or more efficient than the particle bombardment techniques.

Base Sequence↗
PubMed1992

Preservation of Gi-protein inhibited adenylyl cyclase activity in the brains of patients with Alzheimer's disease.

The coupling of inhibitory guanine nucleotide binding (Gi) proteins to the adenylyl cyclase signal transduction complex was compared in 4 brain regions from a series of Alzheimer's disease and matched control subjects by measuring the inhibition of membrane enzyme activities in response to guanosine 5'-[beta gamma-imido]diphosphate (Gpp[NH]p) and aluminium fluoride (AlF4-). Basal adenylyl cyclase activities were significantly lower in preparations of angular gyrus and frontal and temporal cortices, but not cerebellum, from the Alzheimer's disease cases compared to controls. Gpp[NH]p and AlF4- gave significant inhibitions of adenylyl cyclase activity in all brain regions. The magnitude of these inhibitions, when corrected for altered basal activities, were similar for the Alzheimer's disease and control cases. These results indicate that there is no impairment of Gi-protein mediated inhibition of adenylyl cyclase activity in Alzheimer's disease brain.

Adenylyl Cyclases↗
PubMed1992

Embryo-derived platelet activating factor.

Platelet-activating factor (PAF) is secreted by the preimplantation embryo of a number of species. The role of this secretion is yet to be fully elucidated. Evidence to date indicates that it has an important function as an autocrine stimulant of embryonic metabolism, growth and viability. Production of PAF by embryos appears to be severely compromised in vitro. This may be a major cause of reduced embryo viability following embryo culture and it may also help to explain the controversy in the literature regarding the production of PAF by embryos. PAF also alters several aspects of maternal physiology during early pregnancy including endometrial prostaglandin secretion. The significance of these changes remains to be defined.

Animals↗
PubMed1992

Metabolic and developmental responses of preimplantation embryos to platelet activating factor (PAF).

Platelet activating factor (PAF) is an ether phospholipid produced by preimplantation embryos of a number of species. Production of PAF by embryos has been measured by detecting thrombocytopenia in a splenectomized mouse bioassay, platelet aggregation bioassays in vitro and a specific radioimmunoassay. Production is highly variable and is adversely affected by culture in vitro. It has, however, been correlated with morphology, development rates in vitro and the pregnancy potential of embryos following transfer. Investigations using PAF-antagonists have established an essential role for PAF in early pregnancy. Together with studies that have shown PAF to have direct effects on embryonic metabolism during culture in vitro, these observations suggest that PAF acts as an embryonic autocoid. Hence, a major site of action for embryo-derived PAF in vivo is the embryo itself. Supplementation of embryo culture media with PAF had no effect on the rate of development in vitro of 2-cell mouse embryos through to the blastocyst stage. However, PAF increased cell numbers of blastocysts cultured from the 2-cell stage and the mitotic index of embryos at both the 8-cell and blastocyst stages. Supplementation of culture media with PAF has also been shown to increase the implantation potential of both mouse and human embryos cultured in vitro. In the mouse, the effect of PAF in enhancing implantation rates was most evident when the developmental potential of untreated embryos was suboptimal. These observations suggest that the production of embryo-derived PAF is one limiting factor in maintaining the viability of embryos cultured in vitro.

Animals↗
PubMed1992

Actions of platelet activating factor (PAF) on gametes and embryos: clinical aspects.

Platelet activating factor (PAF) is a phospholipid widespread in body tissues. Previous reviews have discussed its production by preimplantation embryos and the evidence implicating it as an autocrine mediator in aspects of gamete and embryo physiology. Human spermatozoa contain variable amounts of PAF, the amount contained depending on the source and method of preparation of the sperm. Incubation of human sperm with PAF tends to increase their forward velocity, especially in samples with slow motility. PAF treatment causes an increase in the proportion of acrosome-reacted sperm and in their ability to penetrate both zona-free hamster ova and cervical mucus. PAF has been found in human follicular fluid at ovulation. A role for PAF in ovulation has been suggested, because PAF antagonists reduce the rate of ovulation in rats. In some studies, modest improvements to mouse in vitro fertilization (IVF) rates have been achieved with PAF supplementation of media under specific conditions. Furthermore, in the rabbit and mouse, PAF antagonists have been reported to inhibit fertilization in vivo and in vitro respectively. However, addition of PAF to human IVF medium, but only at the time of insemination and fertilization, had no effect on either fertilization or pregnancy rates. Sensitive bio- and immuno-assays have shown that PAF is secreted by human embryos into their fluid milieu. PAF secretion by these zygotes during culture, although markedly variable, has been correlated with the achievement of pregnancy and pregnancy outcome. Although the secretion of PAF by the mouse embryo decreases during culture in vitro, exogenous PAF enhances embryo viability during culture. Similarly, culture of human zygotes in PAF-supplemented medium prior to embryo transfer significantly increases the chance of achieving pregnancy. Both the implantation and live-birth rates are increased in human IVF by addition of PAF to the medium.

Embryo, Mammalian↗
PubMed1992

Structural heterogeneity of platelet-activating factor produced by murine preimplantation embryos.

Platelet-activating factor (PAF) is 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine with the alkyl moiety predominantly a mixture of saturated hexadecyl and octadecyl chains (C16:0 and C18:0 PAF, respectively). Previously, a PAF bioassay was compared with a radioimmunoassay for PAF (NEN Du Pont). Both assays were sensitive and quantitative, but the correlation between PAF measured by the bioassay compared to the radioimmunoassay was poor for murine embryo-derived PAF (r = 0.773, n = 88), while being completely adequate (r = 0.961) for a PAF standard which was an equimolar mixture of C16:0 and C18:0 PAF (C16:0/C18:0 PAF). This study compared a larger sample size of murine embryo-derived PAF (n = 154) and found that the poor correlation between the two assays persisted (r = 0.791). When dose-response curves were generated with C16:0, C16:0/C18:0 and C18:0 PAF (over a concentration range of 0.3-30 ng/ml), the concentrations which gave a 50% response were equivalent in the bioassay (i.e. 6 ng/ml), but differed in the radioimmunoassay (i.e. 1.5, 3 and 6 ng/ml, respectively). Following separation of murine embryo-derived PAF (from medium in which 30 two-cell embryos had been cultured for 24 h) into C16:0 and C18:0 PAF by reverse phase high performance liquid chromatography, 9/20 cultures produced 100% C16:0 PAF, 2/20 cultures produced 100% C18:0 PAF and the remaining 9/20 cultures produced varying proportions of both.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Evidence that platelet-activating factor suppresses uterine oxytocin-induced 13,14-dihydro-15-keto-prostaglandin F2 alpha release and phosphatidylinositol hydrolysis in the ewe.

This study was conducted to determine whether platelet-activating factor (PAF) (1) attenuated oxytocin-induced secretion of the prostaglandin (PG) F2 alpha metabolite, PGFM, by the ovine uterus in situ and (2) inhibited the generation of the inositol phosphate secondary messengers by endometrial tissue in response to oxytocin challenge in vitro. Ovariectomized ewes received steroid replacement to mimic the luteal phase. Six ewes received intrauterine injections of 200 micrograms PAF/uterine horn/day on Days 11-15, and 6 ewes were treated with vehicle. All ewes received 1 microgram oxytocin i.v. on Days 13-16. Pretreatment of ewes with PAF significantly suppressed PGFM release in response to oxytocin on Days 14 and 15 (p less than 0.005) compared to vehicle-treated ewes. PAF was not administered on Day 16, and the PGFM response to oxytocin was not different between groups. In a second experiment, ewes were given intrauterine injections of 200 micrograms PAF/uterine horn/day (n = 8) or vehicle (n = 7) on Days 11-15, and all ewes received 1 microgram oxytocin i.v. on Days 13 and 14. On Day 15 the uterus was removed, and the incorporation of 3H-inositol into inositol phosphates was determined in caruncular endometrium. Treatment of ewes with PAF in vivo reduced inositol monophosphate (IP1) generated by oxytocin (10(-6) M) by 56.4%, compared to that in endometrium from vehicle-treated controls, and also inhibited the incorporation of 3H-inositol into glycerophosphoinositol (GPI). If PAF was added to the endometrium during the incubation in vitro, the attenuation of inositol phosphate generation did not occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Adenylyl cyclase activity in postmortem human brain: evidence of altered G protein mediation in Alzheimer's disease.

The effects of agonal status, postmortem delay, and age on human brain adenylyl cyclase activity were determined in membrane preparations of frontal cortex from a series of 18 nondemented subjects who had died with no history of neurological or psychiatric disease. Basal and guanosine 5'-O-(3-thiotriphosphate)-, aluminum fluoride-, and forskolin-stimulated enzyme activities were not significantly reduced over an interval from death to postmortem of between 3 and 37 h and were also not significantly different between individuals dying with a long terminal phase of an illness and those dying suddenly. Basal and aluminum fluoride-stimulated enzyme activities showed a negative correlation with increasing age of the individual. In subsequent experiments, basal and guanosine 5'-O-(3-thiotriphosphate)-, aluminum fluoride-, and forskolin-stimulated enzyme activities were compared in five brain regions from a series of eight Alzheimer's disease and seven matched nondemented control subjects. No significant differences were observed between the groups for either basal activity or activities in response to forskolin stimulation of the catalytic subunit of the enzyme. In contrast, enzyme activities in response to stimulation with guanosine 5'-O-(3-thiotriphosphate) and aluminum fluoride were significantly reduced in preparations of neocortex and cerebellum from the Alzheimer's disease cases compared with the nondemented controls. Lower guanosine 5'-O-(3-thiotriphosphate)-, but not aluminum fluoride-, stimulated activity was also observed in preparations of frontal cortex from a group of four disease controls compared with nondemented control values. The disease control group, which contained Parkinson's disease and progressive supranuclear palsy patients, showed increased forskolin-stimulated activity compared with both the nondemented control and the Alzheimer's disease groups. These findings indicate a widespread impairment of G protein-stimulated adenylyl cyclase activity in Alzheimer's disease brain, which occurs in the absence of altered enzyme catalytic activity and which is unlikely to be the result of non-disease-related factors associated with the nature of terminal illness of individuals.

Adenylyl Cyclases↗