Effect of indomethacin on the cyclic AMP-dependent protein kinase

In vivo and in vitro cardiovascular effects of Papuan taipan (Oxyuranus scutellatus) venom: Exploring "sudden collapse"

'Sudden collapse' following envenoming by some Australasian elapids is a poorly understood cause of mortality. We have previously shown that Oxyuranus scutellatus venom causes cardiovascular collapse in anaesthetized rats. Prior administration of a sub lethal dose of venom attenuated the response to subsequent administration of higher (lethal) venom doses. In this study, we investigated the possible mechanisms mediating this 'protective effect'. Papuan taipan venom (5μg/kg, i.v.) produced a small transient hypotension in anaesthetized rats, while 10μg/kg resulted in a 73±12% decrease in arterial pressure. Venom (20μg/kg or 50μg/kg) produced cardiovascular collapse in all animals tested (n=12). Cardiovascular collapse by 50μg/kg venom was prevented by prior administration of 'priming' doses of venom (5, 10 and 20μg/kg). Also, prior administration of indomethacin (30mg/kg, i.v.) or heparin (300units/kg, i.v.) prevented sudden collapse induced by venom (20μg/kg). Venom was without effect in isolated hearts indicating that a direct cardiac effect was unlikely to be responsible for 'sudden collapse'. Venom induced endothelium-dependent and -independent relaxation in pre-contracted rat mesenteric artery rings which was inhibited by indomethacin, IbTx and Rp-8-CPT-cAMPs. This relaxation was markedly reduced upon second exposure. Our results indicate that cardiovascular collapse induced by O. scutellatus venom may be due to a combination of release of dilator autacoids and to direct relaxation of vascular smooth muscle involving the cAMP/protein kinase A cascade. Further work will involve identification of the venom component(s) responsible for this action and may provide insight into the management of envenomed patients.

Pasteurella haemolytica lipopolysaccharide-induced cytotoxicity in bovine pulmonary artery endothelial monolayers: inhibition by indomethacin

Exposure of bovine pulmonary artery endothelial cells to Pasteurella haemolytica lipopolysaccharide caused severe morphologic changes. Initially, there was dilatation of the rough endoplasmic reticulum and mitochondrial swelling followed by cell retraction, membrane bleb formation, and cell detachment. The affected endothelial cells had severe membrane damage resulting in the leakage of lactate dehydrogenase. Indomethacin in concentrations of 0.5 mM or greater caused marked decreases in the lipopolysaccharide-induced leakage of lactate dehydrogenase. Indomethacin at 5 mM also caused a marked reduction of the lipopolysaccharide-induced morphologic changes resulting in apparent maintenance of the monolayer integrity for 8 hours versus 1 hour in the lipopolysaccharide-treated control. A marked decrease in the cell and nuclear membrane effects resulted, but the rough endoplasmic reticulum dilatation and mitochondrial changes proceeded. These results indicate that indomethacin does not prevent lipopolysaccharide binding but interferes with later events in lipopolysaccharide-induced cytotoxicity in the bovine pulmonary endothelial cell. The concentration of indomethacin required to produce this inhibition suggests that the primary mechanism is not cyclooxygenase inhibition.

Relationship of gonadotropin-releasing hormone, danazol, and prostaglandin blockade to ovarian enlargement and ascites formation of the ovarian hyperstimulation syndrome in the rabbit

The effects of pharmacologic doses of gonadotropin-releasing hormone, danazol, and indomethacin on the clinical and endocrinologic features of the ovarian hyperstimulation syndrome were studied in the rabbit. The ovarian hyperstimulation syndrome was induced with Pergonal (75 IU of follicle-stimulating hormone and 75 IU of luteinizing hormone) and a follicle-stimulating hormone-dominant gonadotropin preparation (85 IU of follicle-stimulating hormone and 53 IU of luteinizing hormone). None of the three agents tested were effective in suppressing the ovarian enlargement and ascites formation in these animals. Ascites developed despite quite significant variations in plasma and intraovarian sex steroid hormone and intraovarian prostaglandin F levels induced by danazol and indomethacin. Ascites develops in hyperstimulated women in association with both follicular and luteal hyperstimulation. In contrast, the ascites response in the hyperstimulated rabbit develops in the presence of follicular hyperstimulation alone without a significant degree of luteal hyperstimulation.

Indomethacin promotes differentiation of Trypanosoma brucei

The treatment of mice with indomethacin lowered Trypanosoma brucei parasitemia 1 to 2 log10 because it quickly promoted the differentiation of rapidly dividing long, slender trypanosomes into short, stumpy forms that do not divide in the mammal but do develop a functional mitochondrion and the ability to infect the tsetse. Since natural resistance correlates with the rate of differentiation, this observation may provide important information about factors that control the severity of trypanosomiasis.

Biochemical studies of the excitable membrane of Paramecium tetraurelia VI. Endogenous protein substrates for in vitro and in vivo phosphorylation in cilia and ciliary membranes

The endogenous protein kinases of isolated Paramecium tetraurelia cilia phosphorylated approximately 30 ciliary polypeptides in vitro. Labeling with [gamma-32P]ATP was not proportional to the amount of each protein in cilia; some minor polypeptides (e.g., 67,000 and 180,000 mol wt) were more heavily labeled than some major polypeptides. Certain of the endogenous substrates for protein kinase were localized in the ciliary membrane (130,000, 86,000, 67,000, and 45,000 mol wt); others were found in axonemes or in both fractions. With cilia from bacterized cultures in the undefined Cerophyl medium, the labeling of specific endogenous phosphate acceptors was altered by pH, cyclic AMP, and cyclic GMP, but the labeling pattern was not affected by the presence of Na+ or K+ (15 mM), Ba++ (5 mM), Ca++ (10(-5) or 10(-4) M), or EGTA. Very similar results were obtained with cilia from cells grown axenically in a semidefined medium; the molecular weights and the extent of phosphorylation of the phosphopolypeptides were comparable to those of cilia from bacterized Cerophyl cultures, although no significant cyclic nucleotide effects were observed in the axenic cilia. Most of the phosphopolypeptides labeled in vitro also turned over rapidly in vitro. The phosphoprotein phosphatase responsible for turnover was partially inhibited by 5 mM NaF. The pattern of ciliary polypeptides labeled in vivo was similar to that observed in the in vitro experiments, although the relative intensities of labeling differed. Six behavioral mutants of Paramecium, known to have defects in the excitable membrane that regulates the ciliary beat, showed normal patterns of ciliary protein phosphorylation in vitro, with and without added cyclic nucleotides, at both pH 6.0 and pH 8.0. The mutants also had apparently normal phosphoprotein phosphatase. The Paranoiac A mutant, however, showed a reduction in cyclic GMP-stimulated protein kinase activity.

Effects of inflammatory agents on endothelial lysosomal fragility and their inhibition by anti-inflammatory drugs

1. Endothelial cells from human umbilical veins were maintained in tissue culture. The fragility of lysosomal membranes were studied by microdensitometry. 2. Histamine (50 microM to 10 mM), 4-methylhistamine (100 nM to 10 mM) and dimaprit (100 nM to 10 mM) increased lysosomal fragility. 2-Thiazolylethylamine and 2-pyridylethylamine (100 nM to 10 mM) had no effect. 3. Prostaglandins E1 and E2 (3 nM to 30 microM) and prostaglandin F2 alpha (2 nM to 20 microM) had no direct effect. Low concentrations of prostaglandins E1 and E2 inhibited the fragility induced by histamine 100 microM. 4. Bradykinin (100 nM to 100 microM) decreased fragility. 5. The increase in fragility induced by histamine 100 microM or dimaprit 100 microM was inhibited by cimetidine (100 microM to 1 mM) but not by mepyramine (1 microM to 1 mM). 6. Pretreatment with indomethacin, hydrocortisone, ibuprofen and sodium salicylate caused a dose-dependent inhibition of histamine-induced fragility. Threshold concentrations were 1 pM, 100 pM, 10 nM and 10 microM, respectively. 7. Lignocaine (1 microM to 1 mM) had no direct effect and did not decrease histamine-induced fragility.

Effect of indomethacin on cardiac beta-adrenergic receptors

Treatment of rats with indomethacin, 1.5 mg/kg per day, for one week, significantly reduced the number of beta-adrenoceptors in the heart without altering their affinity for the specific beta-adrenergic ligand. In indomethacin-treated rats there was a reduction in the cardiac response to epinephrine in vivo as indicated by a shift to the right of the epinephrine dose-heart rate response curve. These results support a possible interference by indomethacin in beta-adrenoceptor-mediated effects.