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Keywords:hepatic aneurysm; portal vein thrombosis; systemic lupus erythematosus; uraemia

Particle formation in the ozone-propylene reaction has been studied using a microprobe system. Size frequencies show that particles are formed by a complex chemical accretion process possibly involving polymeric ozonides. For a given propylene concentration, particle production is found to increase with increasing ozone concentration. Water vapor is found to inhibit partially particle production. Structural characteristics of the chemical constituents of the particles have been studied by IR and NMR.

The aims of the present study were to estimate the fraction of renal brush border membrane Na+-H+ exchange activity mediated by the isoform NHE3 and to evaluate whether the increased brush border Na+-H+ exchange observed in metabolic acidosis is due to increased expression of NHE3 protein. Compared with other isoforms, NHE3 is known to have a unique profile of sensitivity to pharmacologic inhibitors, including relative resistance to amiloride analogs and HOE694. We therefore assessed the inhibitor sensitivity of pH gradient-stimulated 22Na uptake in renal brush border vesicles isolated from normal rats. The I50 values for amiloride (30 microM), dimethylamiloride (10 microM), ethylisopropylamiloride (6 microM), and HOE694 (>100 microM) were markedly dissimilar from those reported for NHE1 and NHE2 but were nearly identical to reported values for NHE3. Na+-H+ exchange activity in renal brush border vesicles isolated from rats with 5 days of NH4Cl-induced metabolic acidosis was increased 1.5-fold compared with control rats, with no change in inhibitor sensitivity. Western blot analysis indicated that NHE3 protein expression was greater in brush border membranes from acidotic compared with control rats. We conclude that virtually all measured Na+-H+ exchange activity in brush border membranes from control and acidotic rats is mediated by NHE3 and that metabolic acidosis causes increased expression of renal brush border NHE3 protein.

Trans-2,5-bis-(3,4,5-trimethoxyphenyl)tetrahydrofuran (L652, 731), a potent and specific receptor antagonist of platelet activating factor (PAF) (Hwang et al., J. Biol. Chem. 260: 15639-15645, 1985), potently inhibits several PAF-induced in vivo responses in rats. Intravenously and p.o. administered L-652,731 gave a dose-response inhibition of PAF-induced lysosomal hydrolase secretion and extravasation with ED50 values of 1 and 3 mg/kg, respectively. Inhibitions of 87% were achieved with 50 mg/kg p.o. After a single 5-mg/kg p.o. dose, L-652,731 achieved 50 to 60% inhibition of PAF-induced lysosomal hydrolase secretion and extravasation by 0.5 to 1.5 hr with near maximum inhibition lasting through 6 hr. A 20-mg/kg p.o. dose of L-652,731 inhibited PAF-induced leukopenia and neutropenia by 96 and 73%, respectively. The most substantial inhibitions of the extravasation and lysosomal hydrolase secretion induced by PAF or soluble immune complexes were achieved by p.o. L-652,731 (20 mg/kg) with moderate inhibition by dexamethasone and little or no inhibition by antagonists/inhibitors of histamine H1 or H2 or serotonin receptors or cyclooxygenase. Intravenous infusion of a 0.4 mg of L-652,731 bolus inhibited the hypotensive responses from subsequent PAF infusions by a maximum of 72% and with a half-life duration of action of 2.5 hr. Intravenous infusion of L-652,731 results in an immediate 87% reversal of the extreme hypotension induced by a previous endotoxin injection. Thus, with its good p.o. activity, long duration of action and specificity in inhibiting PAF-induced responses in vivo, L-652,731 is a very useful tool in determining the role of PAF in mediating different pathophysiological processes.

Nitric oxide (NO) has been shown to play a role in cyclosporin (CsA) nephrotoxicity, but its mechanism of action is still unclear. As inducible NO synthase (iNOS) mRNA has been found to be expressed in rat medullary thick ascending limb (mTAL) cells, we investigated the effects of CsA on NO production in a model of mouse cultured mTAL cells.

Platelet activating factor (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF) induced in isolated rat peritoneal and human peripheral neutrophils a rapid and potent activation of the PAF biosynthetic enzyme acetyl-CoA:1-alkyl-sn-glycero-3-phosphocholine O2-acetyltransferase (EC 2.3.1.67). The PAF-induced activation of the neutrophil acetyltransferase (8-10 times basal neutrophil activity) was maximal within 30 sec after PAF addition, as was the PAF-stimulated degranulation. After 1 min of PAF stimulation, the elevated acetyltransferase activity steadily decreased. Within 2 min of stimulation of neutrophils with 10(-6) M PAF, the 7-fold increase in acetyltransferase activity was coincident with substantial PAF synthesis (as measured by [3H]acetate incorporation into PAF), which was 14% of the PAF synthesis induced by the Ca2+ ionophore A23187 at 10(-5) M. PAF activation of the acetyltransferase and PAF synthesis required intact neutrophils as they did not occur in cells broken by sonication. The neutrophil acetyltransferase was 10-30 times more sensitive to activation by PAF than was degranulation as the acetyltransferase activation was evident with 10(-9) M PAF and was about maximal with 3 x 10(-8) M PAF. The unstimulated and PAF-induced acetyltransferase exhibited the same Km for acetyl-CoA (67 microM), but the Vmax for the PAF-induced enzyme (1667 pmol/min per 10(7) cells) was 10 times that of the unstimulated enzyme (175 pmol/min per 10(7) cells). The PAF induction of the acetyltransferase was less sensitive to inhibition by the specific PAF receptor antagonist L-652,731 than was PAF-induced degranulation. This, along with the differing sensitivities to PAF, suggests that acetyltransferase activation and degranulation induced by PAF either involve two different PAF receptors or involve one receptor type with different receptor occupancy requirements. Escherichia coli alkaline phosphatase, which greatly decreased the activity of the acetyltransferase in spleen microsomes, had little or no effect on the basal or PAF-induced neutrophil acetyltransferase. Thus, by stimulating the activity of acetyltransferase, PAF induces in neutrophils the synthesis of more PAF, thereby probably augmenting the neutrophil response to the initial PAF.

Platelet-activating factor (PAF) is a potent lipid mediator of inflammation and asthma. Using a receptor preparation of rabbit platelet membranes, we identified a novel antagonist of PAF in the methylene chloride extract of a Chinese herbal plant, haifenteng (Piper futokadsura). The active antagonist, kadsurenone, was isolated and characterized in several in vitro and in vivo assays. It is a specific and competitive inhibitor of PAF binding to its receptor with a Ki of 5.8 X 10(-8) M vs. a Ki of 6.3 X 10(-9) M for PAF itself. It inhibits PAF-induced aggregation of rabbit platelets and human neutrophils at 2.4-24 microM, without showing any PAF agonistic activity. It potently inhibits PAF-induced degranulation of human neutrophils at 2.5-50 microM, also without any agonist activity. Kadsurenone is active orally at 25-50 mg/kg of body weight in blocking PAF-induced cutaneous permeability in the guinea pig. It also inhibits PAF-induced increases of hematocrit and circulating N-acetylglucosaminidase in the rat at greater than 10 mg/kg i.p. in a dose-dependent manner. Kadsurenone does not interfere with the function of several pharmacological mediators and receptors tested. Its structural specificity is evidenced by the poor PAF-antagonistic activities of three related structures isolated from the same haifenteng extract.

AbstractCyclosporine (CsA) reduces nitric oxide (NO) production in medullary thick ascending limb (mTAL) cells. We postulated that CsA affected NO secretion in a vectorial manner in polarized renal epithelial cells. The experiments were performed in a model of mTAL sub‐cultured cells. The expression of iNOS in mTAL cells was confirmed by RT‐PCR. The cells were grown on a non‐permeable filter. Nitrite was measured by the modified Griess method. Transepithelial resistance was measured to ensure the integrity of the tight junction. CsA (100 ng/ml) reduced NO production by 22% in mTAL cells. The inhibitory effect was limited to the basolateral side (control: 165 ± 11; plus CsA: 93 ± 17 nM/106cells, P< 0.001) without affecting apical NO secretion. The transepithelial resistance through the epithelial monolayer remained unchanged in CsA‐treated cells. CsA reduced basolateral NO secretion without affecting apical secretion. The results suggest that CsA might affect intra‐renal hemodynamics at the peritubular level.