Pharmacological profile of recombinant, human activated protein C (LY203638) in a canine model of coronary artery thrombosis.

The antithrombotic activity of recombinant, human activated protein C (rh-APC, LY203638) was examined in a model of canine coronary artery thrombosis. Three doses of rh-APC (0.5, 1.0, and 2.0 mg/kg/h) were administered intravenously for 2 h. Whole blood clotting times (thrombin time, activated partial thromboplastin time), ex vivo platelet aggregation, and template bleeding times were determined. Activated partial thromboplastin time significantly increased 2- and 3.7-fold during the 2-h infusion of rh-APC (1.0 and 2.0 mg/kg/h, respectively); thrombin time did not change. Intravenous infusions of rh-APC (1.0 and 2.0 mg/kg/h) produced significant prolongations to occlusion, 186 +/- 21 and 190 +/- 22 min, respectively, compared with the vehicle and the 0.5 mg/kg/h group (86 +/- 12 and 93 +/- 17 min, respectively). Vessel patency was better at the end of the experiment in the intermediate- and high-dose groups (3 of 6 and 3 of 5 vessels, 1.0 and 2.0 mg/kg/h, respectively) compared with the vehicle and 0.5 mg/kg/h groups (0/5 and 0/6, respectively). Only the 1.0 mg/kg/h group was found to have significantly elevated template bleeding times, with peak increases seen 60 min into the drug infusion. All groups had returned to baseline values by the end of the study. There was no observed inhibition of platelet aggregation. These data demonstrate that recombinant, human activated protein C is an effective anticoagulant and antithrombotic agent in the dog.

Intravenous administration of the glycoprotein IIb-IIIa receptor antagonist 7E3 induces reperfusion of an acute thrombotic occlusion of the canine coronary artery.

The ability of the F(ab')2 fragment of the murine monoclonal antibody 7E3 directed against the platelet glycoprotein IIb-IIIa receptor complex, to cause reperfusion of a totally occluding coronary artery thrombus was examined alone and in combination with aspirin and heparin in a canine model of coronary artery thrombosis. A localized thrombus was produced in the left circumflex coronary artery in open-chest dogs by electrolytic injury of the endothelium. Intravenous administration of a single injection of 5.0 mg/kg aspirin and heparin (80 U/kg bolus plus 30 U/kg/hr x 2 hr) maintained vessel patency for approximately 101 +/- 15 minutes. After vessels had been completely occluded for 5 minutes (in the presence of aspirin + heparin), a single intravenous injection of saline (10 ml) or 0.8 mg/kg 7E3 was administered. Reperfusion was observed in all dogs (6 of 6) receiving 7E3; 4 of 6 dogs maintained vessel patency throughout the course of the 2 hour observation period. Activated partial thromboplastin and thrombin times were elevated 1.4 and 9 fold, respectively, in groups that received heparin. Template bleeding times were significantly elevated in the groups receiving 7E3. In the control group, 2 of 5 dogs reperfused briefly, however neither were patent at the end of the observation period. A third group of 4 dogs which did not receive the aspirin + heparin regimen was allowed to occlude and 5 minutes later received a single intravenous injection of 0.8 mg/kg 7E3. None of the 4 dogs in this group reperfused at any time during the study. There were no significant differences between groups in regards to hematological or hemodynamic measurements during the experiment. We concluded from these findings that the monoclonal antibody, 7E3 can promote the dissolution of friable coronary artery thrombi that evolve during standard anticoagulant and antiplatelet therapy.

Antithrombotic assessment of the effects of combination therapy with the anticoagulants efegatran and heparin and the glycoprotein IIb-IIIa platelet receptor antagonist 7E3 in a canine model of coronary artery thrombosis.

BACKGROUND: There is a paucity of data regarding the antithrombotic pharmacology of the drug-drug interactions between the newer anticoagulant and antiplatelet agents. In this investigation, we have studied the antithrombotic effects of combinations of minimum effective doses of the glycoprotein IIb-IIIa receptor antagonist 7E3 [murine F(ab')2] with both heparin and the novel tripeptide arginal antithrombin efegatran (LY294468) in a canine model of coronary artery thrombosis. METHODS AND RESULTS: Thrombogenesis was initiated by electrolytic injury of the intimal surface of the left circumflex coronary artery. The groups studied were efegatran (0.25 mg . kg-1. h-1), heparin (80 U/kg, single injection, plus 30 U . kg-1. h-1), 7E3 (0.4 mg/kg, single injection), 7E3+efegatran, and 7E3+heparin. The combination of 7E3+efegatran was found to maintain better vessel patency (P < .05) at the end of the experiment (4 of 5 vessels) than all other groups (0 of 5, 0 of 4, 1 of 6, 2 of 7, and 1 of 6 for the vehicle-, heparin-, 7E3-, efegatran-, and 7E3+heparin-treated groups, respectively). Bleeding times were increased (P < .05) in both the 7E3+heparin group (fourfold) and the 7E3+efegatran group (threefold). 7E3 alone and both combination treatments produced significant reductions in ADP, arachidonic acid, and thrombin-induced platelet aggregation, whereas efegatran and heparin abolished only thrombin-induced aggregation. CONCLUSIONS: The present investigation demonstrates that combination therapy with minimum effective doses of 7E3+efegatran provided enhanced antithrombotic efficacy compared with 7E3+heparin in this model of thrombosis.

General pharmacology of gemcitabine hydrochloride in animals.

Gemcitabine (2',2'-difluorodeoxycytidine monohydrochloride, LY188011 hydrochloride, CAS 122111-03-9) is a nucleoside analog with a broad spectrum of antitumor activity in murine models and is currently undergoing clinical evaluation. The profile of the pharmacological effects of this agent was assessed in studies evaluating the cardiovascular and respiratory systems, renal function, the gastrointestinal system, the central nervous system, and the autonomic nervous system. In vivo doses ranged from 0.15 to 300 mg/kg given by the intravenous route, while in vitro concentrations up to 1 x 10-3 mol/l were used. Gemcitabine was inactive in the autonomic nervous system, gastrointestinal function, and central nervous system studies. Only minimal changes were seen in the cardiovascular and respiratory study, with a slight decrease in pulmonary arterial pressure at the mid dose and a stroke volume increase at the high dose. In the renal function studies, a slight decrease in the urine pH at the high dose and decreased serum creatinine at the mid dose levels were observed. In summary, gemcitabine had minimal effect in these pharmacodynamic studies. These results indicate that gemcitabine has a low potential to produce adverse pharmacologic effects.

General pharmacology of loracarbef in animals.

Loracarbef ((6R, 7S)-7-[(R)-2-amino-2-phenyl-acetamido]-3-chloro-8-oxo-1- azabicyclo [4.2.0]oct-2-ene-2-carboxylic acid, monohydrate, LY 163892, CAS 121961-22-6) is a carbacephem antibiotic targeted for use in the treatment of infectious disease. The potential pharmacological effects of this agent were examined on cardiovascular, respiratory, gastrointestinal, central nervous and autonomic nervous systems. Also examined were local anesthetic activity, effects on platelet aggregation, circulating blood glucose, primary antibody production, renal function, blood coagulation, ocular irritation, and the acute inflammatory response. Doses of 100, 1000, and 2000 mg/kg given by the oral route were selected for most in vivo studies. Concentrations up to 3 x 10(-3) mol/l were used in vitro. Loracarbef was essentially inactive in the tests of central and autonomic nervous system function, platelet aggregation, renal function, blood hemolysis, primary antibody production, blood coagulation, and ocular irritation. It had no local anesthetic activity. At high oral or intravenous doses, representing significant multiples of the therapeutic dose, loracarbef caused changes in gastrointestinal (decrease in gastric acid production and gastric fluid volume; increased biliary output), cardiovascular (increased mean pressure, cardiac output, heart rate, and femoral flow), blood glucose (increased glucose levels), and anti-inflammatory tests (suppressed acute inflammatory response). In summary, loracarbef exhibited minimal activity in these pharmacodynamic studies. These results indicate loracarbef has a low potential to produce adverse effects at therapeutic doses.

General pharmacology of pergolide in animals. 2nd communication: gastrointestinal, renal and miscellaneous studies.

Pergolide mesylate ((8 beta)-8-[(methylthio)methyl]-6-propylergoline monomethanesulfonate, LY 127809, CAS 66104-23-2) is a novel and potent dopamine agonist marketed for treating the symptoms of Parkinson's disease. The potential secondary pharmacological effects of this agent on the gastrointestinal and renal systems, as well as effects on local anesthesia, hemolysis, platelet aggregation, circulating blood glucose, primary antibody production, and the acute inflammatory response were examined. Pergolide exhibited significant pharmacological effects in gastrointestinal, renal and anti-inflammatory tests at high oral doses. Pergolide was essentially inactive in blood hemolysis, platelet aggregation, primary antibody production and local anesthesia testing. In summary, these studies confirm the pharmacological selectivity of pergolide, and indicate a low potential for secondary pharmacological side effects upon the functions tested at clinically relevant doses.

Comparative pharmacological profile of muscarinic agonists in the isolated ileum, the pithed rat, and the mouse charcoal meal transit test.

1. Several reportedly selective (McN-A-343, M1; RS-86, M2; pilocarpine, M3) and non-selective (oxotremorine, acetylcholine, cis-dioxalone, arecoline, muscarine) muscarinic agonists were examined for comparative pharmacological potency in three diverse models: the guinea pig ileum, the pithed rat, and the mouse charcoal meal transit test. 2. In the guinea pig ileum, all of the compounds examined were associated with concentration-dependent contractions. 3. The apparent order of potency in the isolated ileum was cis-dioxalone greater than acetylcholine greater than oxotremorine greater than arecoline greater than RS-86 greater than pilocarpine greater than McN-A-343. 4. The pA2 values for atropine and pirenzepine in the ileum ranged from 8.4 to 9.4 and 6.1 to 7.7, respectively, indicative of a single receptor, most likely M3. 5. In the mouse charcoal meal transit test, non-selective muscarinic agonists produced dose-dependent increases in gastrointestinal transit, while selective agonists failed to produce any significant changes. 6. Scopolamine methylbromide, a peripherally acting non-selective muscarinic antagonist, significantly reduced the ability of muscarine to increase transit. 7. The compounds were further examined for dose-dependent pressor effects in the pithed rat, which are known to be mediated by stimulation of M1-receptors in sympathetic ganglia. 8. McN-A-343 produced the greatest pressor response, as measured by the percent increase in mean pressure, followed by pilocarpine. 9. Pirenzepine antagonized the pressor response of McN-A-343 and pilocarpine in a dose-dependent manner.

Vancomycin-induced release of histamine from rat peritoneal mast cells and a rat basophil cell line (RBL-1).

Rapid intravenous administration of the glycopeptide antibiotic, vancomycin, may cause a hypotensive reaction which can usually be prevented by infusing vancomycin in dilute solutions. The release of histamine from circulating cells such as basophils and tissue mast cells has been implicated in hypotensive reactions since the effects can be prevented by antihistamine pretreatment. The direct effects of vancomycin on histamine release were therefore investigated in rat peritoneal mast cells and rat leukemic basophils (RBL-1 cells). Suspension cultures of mast cells or RBL-1 cells were exposed to vancomycin for 30-60 minutes at concentrations comparable to those infused clinically (2.28 or 4.56 mg/ml). Vancomycin induced a time- and dose-dependent release of histamine into the culture media from both cell types. The reference degranulating agent, Compound 48/80 (CP 48/80), was also shown to induce histamine release from mast cells and RBL-1 cells. Mast cells were significantly more sensitive to vancomycin and CP 48/80 than RBL-1 cells and, unlike RBL-1 cells, were responsive to the inhibitory effects of cromolyn sodium on histamine release. Cromolyn sodium did not inhibit vancomycin-induced histamine release in RBL-1 or mast cells. Morphologically, mast cells exposed to either vancomycin or CP 48/80 exhibited dose-related degranulation. On the other hand, treatment-related degranulation effects of either vancomycin or CP 48/80 on RBL-1 cells could not be reliably distinguished from controls by qualitative evaluation. Based upon these findings it is concluded that mast cells may represent a more useful model to evaluate the potential of investigational agents to release histamine and to study mechanisms of histamine release than RBL-1 cells.

General pharmacology of a new potent 5-hydroxytryptamine antagonist.

The potential of the investigational 5-hydroxytryptamine (5HT3) antagonist, LY277359, to alter cardiovascular, central nervous system (CNS), smooth muscle, and gastrointestinal functions at multiples of pharmacologically active doses, was examined to provide a profile of possible secondary pharmacological effects. In the anesthetized dog, significant cardiovascular effects were observed at doses 100-1000 and 4-15 times those found to be pharmacologically active at 5HT3 receptors in vivo in rats and dogs, respectively. These effects were limited to decreased heart rate (approximately 20%) at intravenous doses of 1.75 and 3.5 mg/kg and prolonged Q-Tc intervals (approximately 20 to 50%) at doses of 0.438 to 3.5 mg/kg. At an oral dose of 135 mg/kg (representing 1500-4500 times the pharmacologically active dose in rats), LY277359 induced hypoactive behavior and reduced body temperature in mice. Seizure activity was potentiated at high oral doses of LY277359 (45 and 135 mg/kg). A single oral dose of 135 mg/kg increased hexobarbital-induced sleep time. In smooth and cardiac muscle tissue studies in vitro, LY277359 was essentially inactive: it did not alter contractile activity or receptor function of the guinea pig ileum, rat vas deferens, rat uterus, or guinea pig atria at concentrations of 10(-5) to 10(-10) mol/l. At a concentration 50,000 times the 5HT3 antagonistic level in vitro (10(-4) mol/l), LY277359 inhibited the response of the ileum to field stimulation, acetylcholine and angiotensin I, and suppressed the rate of the spontaneously beating guinea pig atria in a noncompetitive manner.(ABSTRACT TRUNCATED AT 250 WORDS)