Cellular interactions and exaggerated arachidonic acid metabolism in rabbit renal injury

Acute cholecystitis potentiates bradykinin stimulated fibroblast prostanoid release in the rabbit

Gallbladder explants from control rabbits and rabbits subjected to bile duct ligation (BDL) for 24 and 72 h (cholecystitis model) were placed in cell culture to determine the source for increased gallbladder prostanoid synthesis during cholecystitis. Cultures from control and 24 h BDL gallbladders grew spindle shaped fibroblasts which did not exhibit increased prostanoid synthesis. 72 h BDL gallbladder cell cultures grew large polygonal shaped cells which appeared to be 'stimulated fibroblasts' by light and electron microscopy and were associated with increased basal and bradykinin stimulated 6-keto-PGF1 alpha release and increased content of prostacyclin synthase when measured by enzyme immunoassay and protein immunoblot analysis respectively. Use of bradykinin antagonists showed that the bradykinin BK2 subtype receptor was the most prominent in the 72 h BDL cell cultures. The 'stimulated fibroblasts' were the source of bradykinin stimulated gallbladder 6-keto-PGF1 alpha synthesis in the inflamed rabbit gallbladder which was mediated by the bradykinin B2 subtype receptor.

The role of prostaglandin I2 and biliary lipids during evolving cholecystitis in the rabbit

BACKGROUND

Acute cholecystitis increases gallbladder prostanoid synthesis. The percent study examined the hypothesis that increased endogenous gallbladder release of prostaglandin I2 (PGI2) after bile duct ligation is caused by both increased ductal pressure and altered biliary lipids.

METHODS

Prostanoid release, biliary lipids, and in vitro fluid absorption of sham gallbladders were compared with those of gallbladders in which acute cholecystitis was induced after common bile duct ligation for 6, 24, and 72 hours.

RESULTS

Bile duct ligation for 6, 24, and 72 hours increased gallbladder PGI2 release twofold and increased gallbladder bile levels of lysolecithin and taurine-conjugated bile acids fivefold compared with sham groups (P < 0.05). In vitro gallbladder fluid absorption was decreased by 50% or more in the 6-, 24-, and 72-hour bile duct-ligated groups (P < 0.05) but was reversed by indomethacin only in the 6-hour ligated group.

CONCLUSIONS

Decreased gallbladder fluid absorption following bile duct ligation for 6 hours was caused by increased gallbladder release of PGI2. Decreased gallbladder fluid absorption following bile duct ligation for 24 and 72 hours was not a prostanoid-mediated process (not reversed by indomethacin) but was associated with increased bile levels of proinflammatory biliary lipids.

Increased gall-bladder prostanoid synthesis after bile-duct ligation in the rabbit is secondary to new enzyme formation

Ligation of the common bile duct (BDL) in the male rabbit resulted in increased gall-bladder microsomal total cyclo-oxygenase activity with prostaglandin E2 (PGE2) and 6-oxoprostaglandin F1 alpha [6-oxo-PGF1 alpha, stable metabolite of prostaglandin I2 (PGI2; prostacyclin)] as the major prostanoids synthesized after 24 and 72 h. Kinetic analysis of gallbladder microsomal membrane fractions incubated with increasing levels of [14C]arachidonic acid indicated that BDL for 24 and 72 h did not change substrate affinity (apparent Km) but markedly increased the rate of conversion (apparent Vmax.) suggesting the presence of more total enzyme responsible for synthesis of 6-oxo-PGF1 alpha and PGE2. BDL for 24 and 72 h significantly increased gall-bladder tissue slice basal release of 6-oxo-PGF1 alpha, but not PGE2, when compared with the controls. Gall-bladder slice release of PGE2 was 3-fold less than 6-oxo-PGF1 alpha in the control gall-bladder slices. Immunoblot analysis of 72 h BDL gall-bladder microsomal membrane fractions showed a slight increase in cyclo-oxygenase content and a 5-fold increase in the content of prostacyclin synthase as compared with the control. These data suggest that the BDL-stimulated total gall-bladder cyclo-oxygenase activity was the result of an increase in the level of specific prostaglandin-synthetic enzymes, in particular prostacyclin synthase, and not from a change in enzyme affinity.

Common bile ligation in the rabbit: an appropriate model for investigating the relationship of endogenous gallbladder prostanoid synthesis with evolving acute inflammation

Gallbladder prostanoid (PG) synthesis and histologic inflammatory changes were compared after 6, 24, and 72 hours of bile duct ligation (BDL) or cystic duct ligation (CDL) in the male rabbit. At each time interval the gallbladder was scored for degree of acute inflammation, examined by radiochromatography for endogenous PG synthesis and analyzed by ANOVA. BDL induced progressive increases in acute inflammation whereas prostanoid synthesis significantly increased only after the 6 and 72 hour groups. Indomethacin treatment inhibited PG synthesis in all BDL groups but only decreased the inflammation score in the 6 and 24 hour BDL groups. CDL did not induce progressive gallbladder inflammatory changes or prostanoid synthesis. These data show that prostanoids are intimately involved with the development of early acute gallbladder inflammation following BDL. Inhibition of PG synthesis could attenuate or retard the progression of early acute gallbladder inflammation if started prior to development of established disease.

Prostaglandin E2 production by dispersed canine fundic mucosal cells. Contribution of macrophages and endothelial cells as major sources

Endogenous prostaglandins (PGs) influence resistance of the gastric mucosa to injury, but the source of PGs is unknown. Using radioimmunoassay, we studied PG production by dispersed canine fundic mucosal cells. PGE2 production, stimulated by bradykinin, epidermal growth factor, zymosan, and calcium ionophore, was greater in the small-cell elutriator fraction (SCEF) than in the medium and large cell fractions, which contained mucous, chief, and parietal cells. Linear density gradients of SCEF cells revealed maximal PGE2 production in cells of light density. Mast, endocrine, and endothelial cells did not account for this PGE2 production. Macrophages, identified by uptake of acetylated-LDL, immunoreactivity with antibodies to the human Ia antigen, and phagocytosis of fluorescent latex particles, were enriched in the SCEF and correlated with PGE2 production in the density gradient. Magnetic separation of cells in the SCEF-ingesting iron particles enriched PGE2 production. Fractions enriched in endothelial cells present in intact capillary fragments, but depleted of macrophages, also produced PGE2. Regulation of PGE2 production differed among cell types. Fibroblasts were easily cultured from submucosa, but were not detected in the SCEF. We conclude that macrophages and capillary endothelial cells are major producers of PGE2 in the canine fundic mucosa.

The cell biology of fibroblast cyclooxygenase

We have prepared polyclonal antisera against sheep seminal vesicles cyclooxygenase (COX) which cross-reacted with human COX. We employed this antisera in studies with human dermal fibroblast cultures to immunoprecipitate selectively the COX enzyme. Labeling of the cells with [35S]-methionine, solubilization of cellular COX followed by its immunoprecipitation, SDS-PAGE electrophoresis and fluorography enabled us to determine directly the synthetic rate of COX protein and its modulation by the monokine interleukin-1 (IL-1). The immunoprecipitated [35S]-labeled COX, as judged from SDS-PAGE electrophoresis, has a molecular size of approximately 73,000 daltons, similar to that of native sheep COX and [3H]-acetyl COX. IL-1 stimulation of enhanced COX synthesis was time and dose dependent; as little as 0.03 units/ml of IL-1 produced significant stimulation of [35S]-labeled COX synthesis. Maximum stimulation was 3-10-fold after preincubation of the cells with IL-1 for 12-16 hours. IL-1 treatment of cells in serum-free media yielded parallel dose response curves for stimulation of PGE2 formation, cellular solubilized COX activity and synthesis of newly formed COX, suggesting that this IL-1 effect is mediated solely via induction of new COX protein synthesis. In contrast, IL-1 effect on cells incubated in the presence of fetal calf serum is more complex. Serum synergistically augments the IL-1 effect on PGE2 synthesis in intact cells but concurrently blunts IL-1 induction of COX synthesis, thus suggesting that a factor (or factors) in serum may stimulate PGE2 production by activating cellular phospholipase(s).

Differential effect of platelet-activating factor (PAF) receptor antagonists on peptide and PAF-stimulated prostaglandin release in unilateral ureteral obstruction

Unilateral ureteral obstruction (UUO) results in increased renal resistance as well as in exaggerated prostaglandin (PG) release from the obstructed hydronephrotic kidney (HNK). We have reported previously that platelet-activating factor (PAF) dose-dependently stimulates the release of PGs from both the HNK and unobstructed contralateral kidney (CLK), with CLK release being 10% that of the HNK. In the present report, we studied the interaction of PAF with its receptor by examining the effects of PAF-receptor antagonists on the release of PGs from the isolated perfused rabbit HNK and CLK stimulated by PAF; angiotensin II (AII), and bradykinin (BK) were also used as agonists. In the HNK, kadsurenone (3 microM) inhibited PAF-stimulated PGE2 and thromboxane B2 (TxB2) release by 28.2 and 62.5% respectively. CV-3988 (20 microM) and triazolam (5 microM) also preferentially diminished PAF-stimulated TxB2 release. In addition, all three drugs significantly diminished BK- and AII-stimulated TxB2 release, while CV-3988 was the only antagonist to affect peptide-stimulated PGE2 release. While effective against agonist-stimulated PG synthesis, these drugs had no direct effect on arachidonic acid metabolism to PGs. Furthermore, in the CLK, CV-3988 had no effect on BK- or AII-stimulated PGE2 release, whereas it totally inhibited PAF-stimulated release of PGE2. These results show that PAF-receptor antagonists in the HNK preferentially inhibit TxB2 release whether stimulated by PAF, AII or BK; in the CLK only PAF-stimulated PG release is affected. This biochemical difference may be of physiological significance and explain some of the functional differences between the HNK and CLK. Therefore, PAF may be an important mediator of some of the biochemical and functional changes associated with UUO.

Effect of endogenously produced leukotrienes and thromboxane on renal vascular resistance in rabbit hydronephrosis

Ureteral obstruction in rabbits is characterized by mononuclear cell invasion of the renal cortex and proliferative fibrosis that is associated with exaggerated prostaglandin synthesis in response to vasoactive and inflammatory cell agonists. In this investigation, we studied the effects of the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) and bradykinin (BK) on eicosanoid synthesis and renal vascular resistance in the ex vivo perfused hydronephrotic kidney (HNK). Administration of fMLP resulted in the dose-dependent synthesis of leukotrienes, thromboxane A2 (TXA2), prostaglandin E2 (PGE2), and prostacyclin (PGI2). Peptidoleukotriene synthesis was monitored by specific radioimmunoassay and by guinea pig ileum bioassay and it was then validated by inhibition of the ileal contractile activity with the peptidoleukotriene receptor antagonist FPL-55712. The leukotrienes produced were identified as LTB4, LTC4, LTD4, and LTE4 by comigration with authentic standards on reverse phase high-performance liquid chromatography (RP-HPLC) and by ultraviolet spectroscopy. BK administration stimulated the synthesis of TXA2, PGE2, and PGI2 but not the synthesis of leukotrienes, in contrast to the results with fMLP, suggesting the involvement of different cell types. Administration of fMLP to the HNK also resulted in a renal vasoconstriction that was partially inhibited by FPL-55712 and that was completely inhibited by the thromboxane synthase inhibitor OKY-1581. Consistent with this result, exogenous administration of LTC4 resulted in the synthesis of TXA2 and in a renal vasoconstriction that was inhibited by either FPL-55712 or OKY-1581.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of endogenously produced leukotrienes, thromboxane, and prostaglandins on coronary vascular resistance in rabbit myocardial infarction

In an effort to evaluate the synthesis and function of eicosanoids in myocardial infarction, we have developed a technique of in vivo myocardial infarction in rabbits followed by ex vivo cardiac perfusion. Isolated Langendorff perfused infarcted hearts (removed 1 or 4 d after infarction) responded to the inflammatory cell agonist N-formylmethionyl-leucyl-phenylalanine (fMLP) with (a) the release of leukotrienes B4, C4, and D4; (b) the release of large amounts of thromboxane (235 +/- 66 ng/5 min), prostacyclin (714 +/- 285 ng/5 min), and prostaglandin E2 (PGE2) (330 +/- 108 ng/5 min); and (c) a coronary vasoconstriction (21.1 +/- 2.5% increase in coronary perfusion pressure) that was specifically inhibited by the peptidoleukotriene receptor antagonist FPL-55712. While noninfarcted hearts challenged with fMLP also released leukotrienes B4, C4, and D4, they released only small amounts of the cyclooxygenase products (thromboxane, 30 +/- 9 ng/5 min; prostacyclin, 120 +/- 54 ng/5 min; PGE2, 27 +/- 10 ng/5 min) and showed minimal vasoconstriction (5.6 +/- 2.1% increase in perfusion pressure). Similarly, hearts challenged with fMLP 30 d following infarction released only small amounts of the cyclooxygenase products (thromboxane, 42 +/- 8 ng/5 min; prostacyclin, 386 +/- 31 ng/5 min; PGE2, 79 +/- 25 ng/5 min). When bradykinin was administered, no leukotrienes were produced, but acutely infarcted hearts released 10 times more thromboxane, prostacyclin, and PGE2 than normal hearts and significantly larger amounts of these products than 30-d infarcted hearts. Histologic analysis showed no inflammatory cells in normal hearts, a prominent polymorphonuclear leukocyte infiltration in 1-d infarcted tissue, fibroblast proliferation with mononuclear cell invasion in 4-d infarcted tissue, and a fibrotic scar with scanty mononuclear cell infiltrate in 30-d infarcted tissue. Inflammatory cell invasion was temporarily associated with augmented cyclooxygenase metabolism, suggesting that infiltrating leukocytes may be responsible for production of thromboxane, prostacyclin, and PGE2 in acutely infarcted hearts. The finding that endogenously produced peptidoleukotrienes are potent coronary vasoconstrictors in infarcted rabbit hearts suggests that these products may contribute to tissue injury in myocardial infarction.

Mechanism of enhanced fibroblast arachidonic acid metabolism by mononuclear cell factor

Chronic inflammation is associated with an infiltration of mononuclear cells, fibroblast proliferation, and elevated levels of prostaglandin (PG) E2. Mononuclear cell conditioned factor (MNCF) medium (5%) stimulated a 100-fold increase in basal human dermal fibroblast PGE2 release over 48 h as compared with fibroblasts that were incubated with control medium (conditioned medium prepared without cells). The MNCF-induced PGE2 production was suppressed by protein synthesis inhibitors. Fibroblasts pretreated with control medium released PGE2 only modestly in response to 1 nM bradykinin for 1 h (basal, 50 +/- 7 pg PGE2/micrograms protein; stimulated, 104 +/- 12 pg PGE2/micrograms protein), whereas cells that had been pretreated with MNCF showed a greatly facilitated bradykinin-induced release of PGE2. (basal, 297 +/- 59 pg PGE2/micrograms protein; stimulated, 866 +/- 85 pg PGE2/micrograms protein). The exaggerated agonist response is not specific for bradykinin because platelet-derived growth factor elicits a similar response. Exogenous arachidonic acid conversion to PGE2 was also facilitated (two- to threefold) by MNCF pretreatment as compared with control. Both the enhanced agonist-stimulated and exogenous arachidonic acid-induced PGE2 release from the MNCF pretreated cells were inhibited by actinomyin D or cycloheximide. A kinetic study of microsomal cyclooxygenase prepared from fibroblasts pretreated with MNCF showed a threefold increase in the maximum velocity (Vmax) but the same Michaelis constant (Km) as control-treated cells. This augmented arachidonic acid metabolism and subsequent enhanced PGE2 production may play an important role in macrophage-fibroblast interactions at sites of inflammation.