Biomedical subjects
A Howarth
Publications and source records attributed to A Howarth.
Intrathecal fibrinolytic therapy after subarachnoid hemorrhage: dosage study in a primate model and review of the literature.
Because of the naturally low fibrinolytic activity of CSF many erythrocytes entrapped in subarachnoid blood clot undergo hemolysis in situ, releasing vasogenic oxyhemoglobin (OxyHb) in high concentrations around the basal cerebral arteries. In order to promote more rapid clearance of erythrocytes from the basal subarachnoid cisterns we are currently investigating intrathecal thrombolytic therapy with human, recombinant, tissue plasminogen activator (rt-PA) in a primate model of subarachnoid hemorrhage (SAH) and cerebral vasospasm (VSP). In the present study 16 monkeys were divided into 4 groups of 4, and each group received a different dose of sustained-release gel rt-PA at the time of experimental SAH. Cerebral angiography seven days later showed that whereas no VSP occurred in the groups receiving 0.5 or 0.75 mg of rt-PA, mild to moderate VSP occurred in the groups receiving 0.125 or 0.25 mg of rt-PA. Analysis of the combined 2 smaller dosage groups revealed significant (P less than 0.05) reduction of lumen caliber in the clot-side internal carotid (C3 and C4), proximal anterior cerebral (A1) and middle cerebral (MCA) arteries. Gross subarachnoid clot remained in all of the animals in the 0.125 and 0.25 mg dose groups, in 2 of the animals in the 0.5 mg dose group, and none of the animals in the 0.75 mg dose group. It was concluded that 0.75 mg of gel rt-PA is sufficient to completely lyse a 4.25 ml SAH and prevent VSP in our primate model. The literature on fibrinolysis and erythrocyte clearance in cerebrospinal fluid (CSF) is reviewed.
Matching for HLA-D region and T-cell antigen receptor gene restriction: fragment length polymorphisms in renal transplantation.
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Modified method for the determination of moxalactam in plasma by high-performance liquid chromatography.
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Leukocyte recruitment in the subcutaneous sponge implant model of acute inflammation in the rat is not mediated by leukotriene B1.
The subcutaneous sponge implant model of acute inflammation in the rat has been evaluated as a suitable test system for evaluating the potential anti-inflammatory efficacy of 5-lipoxygenase inhibitors. The inflammatory parameters measured were exudate volume and leukocyte recruitment. Specific radioimmunoassays were used to measure (1) 5-lipoxygenase (LPO) and cyclo-oxygenase (CO) activity in exudate leukocytes stimulated ex vivo with A23187, and (2) the LTB4 and PGE2 content of inflammatory exudate. The NSAIDs flurbiprofen and indomethacin inhibited cell recruitment, exudate volume and CO activity with ED50S of approximately 1 mg per kg p.o. but failed to inhibit LPO activity at 10 mg per kg p.o. Nafazatrom (Bayer 6575), quercetin and NDGA, which inhibit LPO activity in vitro, were inactive against all parameters when dosed at 100 mg per kg p.o. The "mixed inhibitors" BW755C and phenidone were approximately equipotent inhibitors of LPO activity but BW755C was 10 times more potent than phenidone against CO activity. BW755C was also greater than 10 times more potent at inhibiting cell recruitment and exudate volume than phenidone suggesting that the anti-inflammatory efficacy of the mixed inhibitors reflect their potency against CO rather than LPO activity. Time course studies demonstrated that the inhibitor effects of BW755C and phenidone on leukocyte recruitment reflected a reduction in the PGE2 but not the LTB4 content of the inflammatory exudate. Polyester sponges soaked in high concentrations of LTB4 caused only a modest (2-fold) increase in leukocyte recruitment whilst physiological levels were inactive. The results taken together suggest that CO products make a major contribution to leukocyte recruitment in this model whilst the LPO product LTB4 has little role. This model therefore is of little value for evaluating the anti-inflammatory efficacy of 5-lipoxygenase inhibitors. Moreover, the rat would appear to be unsuitable for evaluating the role of LTB4 in acute inflammation.
The contribution of cyclooxygenase and lipoxygenase products to acute inflammation in the rat.
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The inflammatory response of rabbit skin to topical arachidonic acid and its pharmacological modulation.
The inflammatory reaction induced by the intradermal injection of arachidonic acid into the rabbit dermis has been investigated. Plasma extravasation was measured by the leakage of 125I-albumin into the tissues and polymorphonuclear leukocyte (PMNL) accumulation was assessed histologically. Arachidonic, 5,8,11,14,17-eicosapentaenoic and 8,11,14-eicosatrienoic acids, but not oleic, linoleic or linolenic acids, caused a concentration-related plasma extravasation following their intra-dermal injection. The plasma extravasation induced by arachidonic acid was dependent on PMNLs. PMNL infiltration and plasma extravasation into arachidonic acid-injected skin sites was inhibited by the mixed cyclo-oxygenase-lipoxygenase inhibitor, BW755C. Arachidonic acid-induced plasma extravasation was inhibited by cyclo-oxygenase and 5-lipoxygenase inhibitors but not by the Paf antagonist, kadsurenone. The inflammation induced by arachidonic acid in the rabbit dermis may be a useful model for evaluating 5-lipoxygenase inhibitors which could be potentially useful anti-inflammatory agents for the treatment of psoriasis and other inflammatory diseases.