Biomedical subjects

N S Nicholson

Publications and source records attributed to N S Nicholson.

21 records · Page 2Linked to original sources

PubMed1988

A radioreceptor binding assay for measurement of platelet-activating factor synthesis by human neutrophils.

A new convenient method for the measurement of platelet-activating factor produced in vitro has been developed. This method involves incubation of neutrophils with stimuli, lipid extraction, purification of lipid extracts by normal phase high performance liquid chromatography (HPLC) and quantification of platelet-activating factor (PAF) by a competitive radioreceptor binding assay. The recovery of PAF from the extraction and purification procedures is 94.5 +/- 0.9%. The sensitivity of the assay is 10 pg/tube. Human neutrophils stimulated with 0, 0.25, 0.5, 1 and 2 microM A 23187 will produce ND, ND, 720, 840 and 900 pg of PAF, respectively (ND = not detectable). The values obtained for PAF produced by human neutrophils in the present assay are comparable to those obtained with the rabbit platelet aggregation assay.

Binding, Competitive↗

PubMed1986

Evaluation of a stable 5-F prostacyclin analogue as an antithrombotic agent in haemodialysis.

Prostacyclin has been used as a substitute for heparin in renal dialysis because of its potent antiplatelet activity and its short half-life. However, it is difficult to use because of its instability in neutral buffer and its hypotensive activity at antithrombotic doses. SC-39902, a 5-F prostacyclin analogue, has an ED50 of 17.7 micrograms/kg i.v. against ADP-induced thrombocytopenia in rats. The ED25 for hypotensive activity is 7.0 micrograms/kg i.v. The therapeutic index (blood pressure ED25/antiplatelet ED50) of 0.40 is 3.6 times better than that of PGI2 (0.11). SC-39902 supports clot-free dialysis in dogs at 4.0 micrograms/kg/min (ED100 for dialysis) with a 26% change in blood pressure at the 100% effective dose as compared with 0.052 microgram/kg/min required for PGI2 with a 32% change in blood pressure. The authors conclude that SC-39902 will provide the desirable antiplatelet/antithrombotic activities of PGI2 without instability and buffer incompatability problems. However, at the ED100 for dialysis, SC-39902 does have haemodynamic activity and, thus, a therapeutic index which is greater than four times that of PGI2 in rats is required for a PGI2 analogue to have less hypotensive activity during dialysis.

Animals↗

PubMed1984

Effect of the stable endoperoxide analog U-46619 on prostacyclin production and cyclic AMP levels in bovine endothelial cells.

The effects of the stable endoperoxide analog U46619 (U) on the regulation of prostacyclin (PGI2) formation and cyclic adenosine monophosphate (cAMP) were investigated in cultured bovine aortic endothelial (BAE) cells. Incubation of U (0.3, 3.0 and 30 microM) with BAE cells for 5 min results in a dose-dependent increase in PGI2. Cyclic AMP levels were not changed at 0.3 and 3.0 microM but were stimulated at 30 microM U. When cells were exposed to U for a second and third 5 min period, PGI2 formation at 0.3 and 3.0 microM U remained stimulated while at 30 microM, PGI2 was not increased. Five min incubation of BAE cells with the cyclooxygenase inhibitor indomethacin blocked the stimulation of PGI2 at all concentrations of U and also prevented the increase of cAMP levels at 30 microM. In cells prelabeled with 3H-arachidonate, U stimulated release of labeled products at 0.3 and 3.0 microM but not at 30 microM U. In cells treated with bradykinin in the presence of U, PGI2 production was stimulated at 0.3 and 3.0 microM but not 30 microM U. When cells were exposed to U and stimulated with PGI2 (with and without phosphodiesterase inhibition), U caused significant increases in cAMP. We conclude that incubation of BAE cells with U results in an initial dose-dependent increase in PGI2 formation. Cyclic AMP levels are increased at high concentrations of U. This increase in cAMP is mediated by the initial stimulated PGI2 and results in decreased PGI2 on further exposure to U. Data suggest that U stimulates phospholipase activity and, at high concentrations, inhibits phosphodiesterase.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗