Gryglewski Rj

Arterial walls are protected against deposition of platelet thrombi by a substance (prostaglandin X) which they make from prostaglandin endoperoxides

Prostaglandin (PG) endoperoxides (PGG2 and PGH2) contract arterial smooth muscle and cause platelet aggregation. Microsomes from pig aorta, pig mesenteric arteries, rabbit aorta and rat stomach fundus enzymically transform PG endoperoxides to an unstable product (PGX) which relaxes arterial strips and prevents platelet aggregation. Microsomes from rat stomach corpus, rat liver, rabbit lungs, rabbit spleen, rabbit brain, rabbit kidney medulla, ram seminal vesicles as well as particulate fractions of rat skin homogenates transform PG endoperoxides to PGE- and PGF- rather than to PGX-like activity. PGX differs from the products of enzymic transformation of prostaglandin endoperoxides so far identified, including PGE2, F2alpha, D2, thromboxane A2 and their metabolites. PGX is less active in contracting rat fundic strip, chick rectum, guinea pig ileum and guinea pig trachea than are PGG2 and PGH2. PGX does not contract the rat colon. PGX is unstable in aqueous solution and its antiaggregating activity disappears within 0.25 min on boiling or within 10 min at 37degrees C. As an inhibitor of human platelet aggregation induced in vitro by arachidonic acid PGX was 30 times more potent than PGE1. The enzymic formation of PGX is inhibited by 15-hydroperoxy arachidonic acid (IC50 = 0.48 mug/ml), by spontaneously oxidised arachidonic acid (IC 50 less than 100 mug/ml) and by tranylcypromine (IC50 = 160 mug/ml). We conclude that a balance between formation by arterial walls of PGX which prevents platelet aggregation and release by blood platelets of prostaglandin endoperoxides which induce aggregation is of the utmost importance for the control of thrombus formation in vessels.

A lipid peroxide inhibits the enzyme in blood vessel microsomes that generates from prostaglandin endoperoxides the substance (prostaglandin X) which prevents platelet aggregation

Microsomal fractions from arterial walls of pigs and rabbits and fundus of rat stomach generate from prostaglandin endoperoxides (PGG2 or H2) an unstable substance, prostaglandin X (PGX) which is a potent inhibitor of platelet aggregation induced by several different substances. Other microsomal fractions including corpus of stomach, lung and ram seminal vesicles generate smaller amounts of PGX from PGG2 or PGH2. Incubation of microsomes from arterial wall or fundus of stomach with platelet-rich plasma under various conditions shows that the enzyme which generates PGX can utilize endoperoxides liberated from platelets or added to the cuvette, thereby preventing, interrupting or reversing the process of platelet aggregation. The generation of PGX is strongly inhibited (IC50 0.43 mug/ml) by 15-hydroperoxy arachidonic acid. These observations are important in the interpretation of vascular diseases such as atherosclerosis and thrombosis and provide a rational basis for the use of anti-oxidants in the prevention and treatment of these diseases.

Corticosteroids inhibit prostaglandin release from perfused mesenteric blood vessels of rabbit and from perfused lungs of sensitized guinea pig

Infusion of norephinephrine (NE) (1 - 3 mug/ml/min) into the isolated mesenteric vascular preparation of rabbit resulted in a rise in perfusion pressure, which was associated with the release of prostaglandin E-like substance (PGE) at a concentration of 2.81 +/- 0.65 ng/ml in terms of PGE2. Indomethacin (3 mug/ml) abolished the NE-induced release of PGE. Arachidonic acid (0.2 mug/ml) in the presence of indomethacin did not restore the NE-induced release of PGE. Hydrocortisone (10 - 30 mug/ml) and dexamethasone (2 - 5 mug/ml) also inhibited the NE-induced release of PGE. The inhibitory action of both corticosteroids was abolished by arachidonic acid (0.2 mug/ml). Antigen-induced release of a prostaglandin-like substance (PGs) (43.1 +/- 3.8 ng/ml in terms of PGE2 and a rabbit aorta contracting substance (RCS) from perfused lungs of sensitized guinea pigs was completely abolished by indomethacin (5 mug/ml) or by hydrocortisone (100 mug/ml). Indomethacin, however, increased histamine release up to 280% of the control level, which was 470 +/- 54 ng/ml, while hydrocortisone diminished histamine release down to 30% of the control level. A superimposed infusion of arachidonic acid (1 mug/ml) into the pulmonary artery reversed the hydrocortisone-induced blockade of the release of RCS and PGs. It may be concluded that corticosteroids neither inhibit prostaglandin synthetase nor influence prostaglandin transport through the membranes but they do impair the availability of the substrate for the enzyme.

Aspirin-induced Asthma

Abstract Eighteen patients with asthma and aspirin hypersensitivity have been challenged with increasing doses of aspirin, fenoprofen, ibuprofen, and dextropropoxyphene. Low doses of the first three drugs induced bronchoconstriction in all the patients as evidenced by fall in peak expiratory flow and appearance of clinical symptoms. There were no reactions to therapeutic doses of dextropropoxyphene. Aspirin, fenoprofen, and ibuprofen, but not dextropropoxyphene, inhibited prostaglandin synthetase activity in three different microsomal preparations, i.e., in bovine seminal vesicles, in rabbit brain and, in rabbit kidney medulla. Expected in vivo antienzymic potency of a drug, calculated from experiments using rabbit brain microsomes, corresponded roughly with its potency to induce bronchoconstriction in the challenge tests. An individual pattern of sensitivity to threshold doses of prostaglandin, synthetase inhibitors was demonstrated for each patient. The results obtained suggest that precipitation of asthmatic attacks by nonsteroidal anti-inflammatory drugs is mediated through inhibition of prostaglandin biosynthesis. The degree of enzymic inhibition, which is sufficient to precipitate bronchoconstriction, is an individual hallmark. Knowing the threshold dose for any of prostaglandin synthetase inhibitors in a patient, one can predict the threshold doses for the rest of aspirin-like drugs in this particular patient.

The effect of 4-acetamidophenol on prostaglandin synthetase activity in bovine and ram seminal vesicle microsomes

Abstract The effect of paracetamol (4-acetamidophenol) on PG synthetase activity was tested in bull (BSVM) and ram (RSVM) seminal vesicle microsomes. In the presence of glutathione (165 μM) and hydroquinone (45 μM) in BSVM paracetamol (up to 67 μM) had no effect or inhibited ( IC 50 = 1500 μ M ) the enzymic activity. In the absence of cofactors paracetamol (67–667 μM) stimulated the generation of PGs in BSVM. Also in RSVM paracetamol (33–333 μM) stimulated PG and malondialdehyde generation as well as oxygen consumption, provided that the exogenous cofactors were omitted from the incubation mixture. Hydroquinone (150 μM) was able to abolish the stimulatory effect of paracetamol on the enzymic activity. We conclude that paracetamol can replace hydroquinone and other cofactors for cyclo-oxygenation of arachidonic acid in BSVM and RSVM. The inhibitory effect of paracetamol on PG synthetase activity occurs only in the abundance of exogenous cofactors in the microsomal preparation.

Thrombolytic action of ticlopidine: possible mechanisms

Ticlopidine (Ticlide), an anti-platelet drug with a broad scope of clinical applications, is claimed to be an antagonist of adenosine diphosphate on platelet receptors. In vitro this antagonism cannot be demonstrated. Ex vivo it is detectable many hours after oral administration of the drug, perhaps subsequently to its biotransformation to an unknown metabolite. Here, we report for the first time that in patients with peripheral arterial disease and in cats with extracorporal circulation ticlopidine evokes instantaneous thrombolytic or fibrinolytic effects which are not associated with inhibition of platelet aggregation. Shortening of euglobulin clot lysis time and increase in plasma levels of tissue plasminogen activator were observed 1-2 h after oral ingestion of ticlopidine at a single dose of 500 mg. In cats ticlopidine produced instantaneous anti-thrombotic and thrombolytic effects at doses of 0.3-1 mg/kg and 10-15 mg/kg i.v., respectively. Thrombolysis by ticlopidine (10 mg/kg i.v.) was comparable to that by prostacyclin at a dose of 0.3 microgram/kg i.v. Ticlopidine at a concentration of 100 microM increased endothelial thromboresistance in vitro. The drug did not inhibit the activity of cyclooxygenase-1 or 12-lipoxygenase while it inhibited lipid autooxidation (IC50 = 18 microM) in rat liver microsomes. Our data point to a possibility that the therapeutic efficacy of ticlopidine might be associated not only with its delayed anti-platelet effects but also with its immediate thrombolytic action which is likely to be mediated by endothelial prostacyclin and tissue plasminogen activator rather than by platelet mechanisms.

Comparison of Endothelial Pleiotropic Actions of Angiotensin Converting Enzyme Inhibitors and Statins

Abstract: Two in vitro and one in vivo assay were performed to study the endothelial pleiotropic actions of “tissue type” angiotensin converting enzyme inhibitors (ACE‐Is) such as perindopril and quinapril, their active forms, that is, quinaprilat and peridoprilat, or of statins belonging to natural (lovastatin), semisynthetic (simvastatin), and synthetic enantiomeric (atorvastatin, cerivastatin) classes. Cytoplasmic [Ca2+]i levels in cultured bovine aortic endothelial cells and endothelium‐dependent nitric oxide‐mediated coronary vasodilatation in the Langendorff preparation of guinea pig heart constituted our in vitro assays. The in vivo assay consisted of study of PGI2‐mediated thrombolytic response in arterial blood of rats after intravenous administration of drugs. In this last assay, perindopril and quinapril proved to be, by two orders of magnitude, more potent PGI2‐dependent thrombolytics than the most potent statin (atorvastatin). However, in both in vitro assays we found a higher endothelial efficacy of statins as compared to ACE‐Is. In particular, those statins that contain the lactone ring in their molecules (lovastatin, simvastatin) were the most potent coronary vasodilators. In summary, the in vivo profile of action of ACE‐Is and statins contrasted with their reversed order of potency in vitro. We hypothesize that the endocrine‐like function of the pulmonary circulation [28‐31] may be responsible for the in vivo bradykinin‐triggered, PGI2‐mediated thrombolysis by ACE‐Is, whereas the pleiotropic action of statins, possibly involving inhibition of prenylation [14‐19], is diffused throughout many vascular beds.

Prostacyclin, Nitric Oxide, and Atherosclerosisa

Disorders in arterial production of PGI2 and NO occur in atherosclerosis. Exogenous PGI2 and NO are capable of interacting pharmacologically. We claim that no such direct interactions occur between endogenous endothelial PGI2 and NO. Studying mechanisms of cardiac reactive hyperemia in guinea pigs and of thrombolysis in cats, we surmise that in vivo vascular intima releases PGI2 intraluminally while NO is secreted abluminally and thus these two ephemeral mediators do not see each other. Hence, in any disease, the disturbances in endothelial generation of PGI2 or NO have to be scrutinized separately. It may well be that endogenous PGI2 maintains endothelial thromboresistance while NO controls arterial myocytes and tissues in which microcirculation is embedded. These responsibilities remain unshared. Interactions between PGI2 and NO are confined to pharmacological domains.

Protective Role of Pulmonary Nitric Oxide in the Acute Phase of Endotoxemia in Rats

We present for the first time direct continuous assay of NO concentration (porphyrinic sensor) in the lung parenchyma of Sprague-Dawley rats in vivo during endotoxemia. Intravenous infusion of lipopolysaccharide (LPS, 2 mg x kg(-1) x min(-1) for 10 minutes) stimulated an acute burst of NO from constitutive NO synthase (NOS) that peaked 10 to 15 minutes after the start of LPS infusion, mirroring a coincident peak drop in arterial pressure. NO concentration declined over the next hour to twice above pre-LPS infusion NO levels, where it remained until the rats died, 5 to 6 hours after LPS infusion. The chronic drop in arterial pressure observed from 70 minutes to 6 hours after the start of LPS infusion was not convincingly mirrored by a chronic increase in NO concentration, even though indirect NO assay (Griess method, assaying NO decay products NO2-/NO3-) showed that NO production was increasing as a result of continuous NO release by inducible NOS. A NOS inhibitor, N(omega)-nitro-L-arginine (L-NNA, 10 mg/kg i.v.) injected 45 minutes before LPS infusion, resulted in sudden death accompanied by macroscopically/microscopically diagnosed symptoms similar to acute respiratory distress syndrome <25 minutes after the start of LPS infusion. Pharmacological analysis of this L-NNA+LPS model by replacing L-NNA with 1-amino-2-hydroxy-guanidine (selective inhibitor of inducible NOS) or by pretreatment with S-nitroso-N-acetyl-penicillamine (NO donor), camonagrel (thromboxane synthase inhibitor), or WEB2170 (platelet-activating factor receptor antagonist) indicated that in the early acute phase of endotoxemia, LPS stimulated the production of cytoprotective NO, cytotoxic thromboxane A2, and platelet-activating factor.

Umbilical arteries of babies born to cigarette smokers generate less prostacyclin and contain less arginine and citrulline compared with those of babies born to control subjects

OBJECTIVE The hypothesis of this study was that umbilical arteries of babies born to smoking mothers produce less nitric oxide and prostacyclin than do those of nonsmoking mothers. STUDY DESIGN L-Arginine, L-citrulline, L-cysteine, and prostacyclin were measured in the umbilical arteries of 11 babies born to smoking mothers and 16 infants born to nonsmoking controls. The concentrations in the two groups were compared with the modified t test. RESULTS The generation of prostacyclin was reduced in the umbilical arteries of infants of smoking mothers. Similarly, L-arginine and L-citrulline, but not L-cysteine levels, in these arteries were suppressed compared with those of the nonsmoking controls. CONCLUSION Along with the known direct vasoconstrictive effect of nicotine, nitric oxide and prostacyclin deficiency may affect the uteroplacental blood flow and contribute to the impaired fetal nutrition and increased perinatal mortality of babies born to women who smoke.