Single bolus administration of recombinant tissue plasminogen activator: effects on infarct related vessel patency, microvascular perfusion, and microvascular reocclusion in a canine model of thrombotic occlusion/reperfusion.

STUDY OBJECTIVE: The aim was to evaluate the thrombolytic efficacy of recombinant double chain tissue plasminogen activator (Duteplase, t-PA) given as a single intravenous bolus versus an infusion in a canine model of coronary arterial occlusion/reperfusion. DESIGN: Coronary arterial thrombi were induced by a copper coil (placed under fluoroscopic control) in the left anterior descending coronary artery of anaesthetised dogs. Following 90 min thrombotic occlusion, animals were randomly assigned to one of two treatment groups: group 1 = t-PA infused intravenously at 0.6 x 10(6) IU.kg-1.h-1, or group 2 = t-PA (0.6 x 10(6) IU.kg-1) by intravenous bolus over 6 min. Both groups received concurrent heparin (six 1000 IU boluses, + 100 IU.kg-1.h-1) throughout t-PA administration and the 2 h reperfusion period. SUBJECTS: 16 beagle dogs of either sex were used, weight 9.2-20.3 kg. MEASUREMENTS AND MAIN RESULTS: Radiolabelled microspheres were injected to assess microvascular coronary flow at various time points throughout the experimental period. Infarct related vessel patency (IRVP) was assessed arteriographically every 5 min. Infarct size was assessed histochemically at the end of the reperfusion period. IRVP was achieved within 42.9 (SEM 7.4) min and 43.1(7.0) min for infusion and bolus groups respectively; 60 min patency rates were 88% for both groups. t-PA restored full microvascular flow to ischaemic subendocardial and subepicardial regions in both groups compared to initial preocclusion regional blood flow. Extent of reactive hyperaemia was greater in infusion than bolus treatment animals: infusion group 1.18(0.15) v bolus group 0.72(0.14) ml.min-1.g-1 (subepicardial). Degree of microvascular reocclusion at 120 min reperfusion was similar for both groups despite aggressive anticoagulation throughout: infusion group 0.33(0.08) v bolus group 0.42(0.11) ml.min-1.g-1 (subendocardial). Areas of the myocardium at risk (R), absolute infarct size (I), and infarct risk ratio (I/R) were similar for both groups: R = 33.9(1.5) v 30.9(1.9)%; I = 15.9(3.1) v 13.3(3.1)%; I/R = 46.3(8.4) 42.1(9.2)%. Degree of systemic fibrinogenolysis was similar for both groups: infusion 1.65(0.40) to 0.67(0.07) g.litre-1 v bolus 1.68(0.15) to 0.96(0.12) g.litre-1. CONCLUSIONS: Single bolus administration of t-PA showed equivalent efficacy to infusion dosing in respect of IRVP, microvascular reperfusion, and microvascular reocclusion. As a result the degree of tissue necrosis (I/R ratio) was no different when comparing the two dosing regimens. Similar degrees of systemic fibrinogenolysis were observed for both treatment groups.

Enhanced myocardial salvage by maintenance of microvascular patency following initial thrombolysis with recombinant tissue plasminogen activator.

STUDY OBJECTIVE: The aim was to examine the value of a subthrombolytic maintenance infusion of recombinant double chain tissue plasminogen activator (BW t-PA, Duteplase) in preserving microvascular coronary flow following initial thrombolysis. DESIGN: Coronary arterial thrombi were induced by a copper coil (placed under fluoroscopic control) in the canine left anterior descending coronary artery. Complete vessel occlusion occurred within 10-15 min of coil placement. Following 90 min of thrombotic occlusion, animals received one of three treatments: group 1, vehicle 0.9% saline; group 2, t-PA 1.0 X 10(6) IU.kg-1.h-1 for 1 h; group 3, t-PA 1.0 X 10(6) IU.kg-1.h-1 for 1 h followed by 0.12 X 10(6) IU.kg-1.h-1 throughout the 2 h reperfusion period. Radiolabelled microspheres were administered to assess microvascular coronary flow at various time points throughout the experimental period. SUBJECTS: Experimental subjects were beagle dogs of either sex (n = 30), weight 8.9-14.3 kg. MEASUREMENTS AND MAIN RESULTS: Main vessel patency (assessed fluoroscopically) was achieved within 40.0(SEM 4.0) min and 37.0(3.1) min for group 2 and group 3 animals respectively. Group 1 animals did not reperfuse. Full microvascular coronary flow was achieved following the lytic infusion of t-PA. However, microvascular flow to the ischaemic zone was significantly reduced at the end of the 2 h reperfusion phase in group 2 animals despite "aggressive" anticoagulation with heparin throughout the reperfusion period: subendocardial flow decreased from 0.74(0.14) to 0.24(0.08) ml.min-1.g-1; subepicardial flow decreased from 0.82(0.13) to 0.36(0.09) ml.min-1.g-1, p less than 0.05. Microvascular coronary flow to the ischaemic zone was better preserved following the maintenance infusion of t-PA given throughout the reperfusion phase: subendocardial flow decreased from 0.95(0.07) to 0.50(0.10) ml.min-1.g-1; subepicardial flow decreased from 0.73(0.04) to 0.52(0.08) ml.min-1.g-1. Thrombolytic reperfusion led to salvage of the ischaemic myocardium, with infarct/risk ratio decreasing from 75.0(10.0)% in group 1 to 46.3(11.0)% in group 2, p less than 0.05. Further salvage of the ischaemic myocardium followed a lytic plus maintenance infusion of t-PA, with infarct/risk ratio decreasing to 35.5(6.7)% but this did not reach statistical significance. CONCLUSIONS: t-PA consistently achieved main vessel reperfusion within 40 min (mean) of instituting therapy in our model, leading to marked salvage of ischaemic myocardium. The data also suggest that maintenance infusion of t-PA helps preserve microvascular coronary flow throughout reperfusion and tends to reduce infarct size further.

The antagonism of adrenergic neurone blockade by amphetamine and dexamphetamine in the rat and guinea-pig.

1. In isolated rat mesentery preparations, intra-arterial injection of the following drugs rapidly suppressed vasoconstrictor responses to sympathetic nerve stimulation: bretylium (75-100 mug), guanethidine (10-20 mug) and bethanidine (20-30 mug); with phenoxypropylguanidine (15-30 mug) the onset of blockade was slower. The blockade caused by these or higher concentrations was rapidly abolished by intra-arterial injection of amphetamine (100 mug) as also was the blockade caused by infusing bretylium or guanethidine for 10-20 min. Partial blockade was produced by 20 mug of reserpine and this was only slightly and briefly antagonized by amphetamine.2. In mesentery preparations taken from rats 24 h after subcutaneous injection of bretylium 50 mg/kg, guanethidine 10 mg/kg, phenoxypropylguanidine 10 mg/kg or reserpine 0.1 mg/kg, responses to sympathetic nerve stimulation were greatly impaired. Only in the preparations from the bretylium-treated rats did amphetamine antagonize the blockade. The adrenergic neurone blocking effect of bethanidine 10 mg/kg was evident at 12 h but not at 24 h after injection.3. In rat mesentery amphetamine did not cause vasoconstriction but briefly potentiated the vasoconstrictor effect of sympathetic nerve stimulation. Responses to noradrenaline were not importantly affected.4. The contractile responses of the rat inferior eyelid caused by stimulation of the cervical sympathetic nerve was greatly reduced 17-27 h after subcutaneous injection of bretylium 300 mg/kg, bethanidine 30 mg/kg, guanethidine 10 mg/kg or reserpine 0.3 mg/kg. Intravenous dexamphetamine (0.5 mg/kg) powerfully antagonized the effect of bretylium, weakly antagonized the blockade by bethanidine and guanethidine and caused no change in the response of reserpine-treated animals.5. The vas deferens taken from guinea-pigs 24 h after subcutaneous injection of either bretylium or guanethidine showed greatly impaired responses to hypogastric nerve stimulation. Amphetamine largely restored the contractile response in bretylium-treated rats but caused only weak antagonism in the guanethidine-treated animals.

BW A575C, a chemically novel agent with angiotensin converting enzyme inhibitor and beta-adrenoceptor-blocking properties.

BW A575C (N-(1-(S)-carboxy-5-[4(3-isopropylamino-2-(R, S)-hydroxypropoxy)indole-2- carboxamido]pentyl)-(R, S)-alanyl-(S)-proline) is a chemically novel agent which exhibits in a single molecule both angiotensin converting enzyme (ACE) inhibition and beta-adrenoceptor-blocking properties. BW A575C produced a competitive blockade of heart rate responses to isoprenaline in a guinea-pig right atrial preparation (pKB 7.18 +/- 0.05, cf. pindolol 8.9 +/- 0.7). BW A575C inhibited a partially purified preparation of ACE obtained from rabbit lung (IC50 10.7 +/- 2.1 nM, cf. enalaprilat, 4.4 +/- 0.8 nM). Intravenous administration of BW A575C (1-100 micrograms kg-1 min-1) to the pithed rat inhibited in a dose-dependent fashion both angiotensin I-induced pressor responses and isoprenaline-induced tachycardia. Dose-ratios obtained from such studies demonstrated that, in this preparation, BW A575C was approximately 100 times more active as an ACE inhibitor than as a beta-adrenoceptor blocking agent. Intravenous administration of BW A575C (1 mg kg-1) to the conscious rat inhibited angiotensin I-induced pressor responses, being approximately equipotent to enalapril and 10 times more potent than captopril. At the same dose, BW A575C had a similar duration of action as an ACE inhibitor to enalapril. Intravenous administration of BW A575C (1 mg kg-1) to either conscious dogs or rats inhibited both angiotensin I-induced pressor responses and isoprenaline-induced heart rate responses. Dose-ratios obtained from such studies demonstrated that in these species, BW A575C was 2-10 times more active as an ACE inhibitor than as a beta-adrenoceptor blocking agent.

BW A256C, a chemically novel class 1 antiarrhythmic agent. A comparison of in vitro and in vivo activity with other class 1 antiarrhythmic agents.

BW A256C (5(3)-amino-6-(2,3-dichlorophenyl)-2,3(2,5)-dihydro-3(5)-imino-2 -isopropyl-1,2,4-triazine) is a novel class 1 antiarrhythmic agent designed to combine the features of potency with reduced central nervous system penetration. BW A256C reduced the maximum rate of depolarization of guinea-pig ventricle and dog Purkinje fibres in vitro (EC50, 2.2 X 10(-6) M and 1.8 X 10(-6) M, respectively), being significantly more potent than quinidine, lidocaine, disopyramide and flecainide. BW A256C was also more potent than these agents at inhibiting aconitine-induced arrhythmias in anaesthetized rats; however, unlike these agents, BW A256C was devoid of hypotensive activity at antiarrhythmic doses. In anaesthetized dogs, intravenous administration of BW A256C (0.25-1 mg kg-1) caused a dose-dependent suppression of ventricular arrhythmias that occurred on reperfusion of an occluded coronary artery. In conscious dogs, intravenous infusion (total dose, 1.5 mg kg-1) or oral administration of BW A256C (1.25-5 mg kg-1) caused dose-dependent suppression of the ventricular ectopic activity that occurred following 20-24 h of permanent coronary artery ligation. In the conscious dog, BW A256C was approximately 7 times more potent and was also longer acting than flecainide. Administration of BW A256C was not associated with any evidence of peripheral or CNS toxicity. However, plasma levels 3-4 times greater than the antiarrhythmic levels were associated with a proarrhythmic activity.

A comparative study of the cardiovascular and biochemical actions of the imidazo [4,5b] pyridine sulmazole and an imidazo [4,5c] pyridine analogue, BW A746C.

1. BW A746C is a chemical analogue of the imidazo [4,5b] pyridine, sulmazole (AR-L115 BS). Like sulmazole, BW A746C possesses positive inotropic and vasodilator activity in vivo. 2. In anaesthetized guinea-pigs, dogs and primates, a bolus i.v. injection of BW A746C, (0.001-1.0 mg kg-1) caused a significant, dose-related increase in ventricular dP/dt, and reduction in diastolic blood pressure, with small increases in heart rate. In these species, a significantly higher dose of BW A746C was required to lower blood pressure by 30% from basal, than was needed to raise ventricular dP/dt by 50% over basal. 3. In anaesthetized guinea-pigs and dogs, bolus i.v. injections of sulmazole (0.1-10.0 mg kg-1) caused similar effects to those observed with BW A746C. In these species, however, there was no significant difference between the dose of sulmazole required to lower blood pressure by 30% from basal and that required to raise ventricular dP/dt by 50%. 4. In conscious dogs, i.v. infusion of BW A746C (to a total dose of 0.3 mg kg-1) caused a significant increase in ventricular dP/dt, but no significant change in either diastolic blood pressure or heart rate. 5. In cell-free biochemical assays, there were no clear differences between the observed activities of BW A746C and sulmazole. Both compounds are cyclic nucleotide phosphodiesterase inhibitors with similar potencies and selectivities for the Type III enzyme (IC50 BW A746C = 3.0 +/- 0.5 X 10(-5) M, sulmazole 5.0 +/- 1.9 X 10(-5) M). The compounds had little or no effects on sarcolemmal Na+/K+-ATPase, Ca2+ ATPase or Na+/Ca2+ exchange, and sulmazole, but not BW A746C, had a small, stimulatory effect on myofibrillar ATPase. 6. In anaesthetized guinea-pigs and dogs, BW A746C was significantly more potent as a positive inotrope than sulmazole. In contrast with sulmazole, BW A746C produced its inotropic effects at significantly lower doses than those required to reduce diastolic blood pressure. This was also apparent from the results obtained in the anaesthetised primates and the conscious dogs. It was therefore concluded that the inotropic/vasodilator profile of BW A746C favours its positive inotrope activity. This profile cannot be explained on the basis of any biochemical differences from sulmazole.

The cardiovascular and platelet actions of 9 beta-methyl carbacyclin (ciprostene), a chemically stable analogue of prostacyclin, in the dog and monkey.

9 beta-Methyl carbacyclin (9 beta Me; ciprostene) is a synthetic, chemically stable analogue of prostacyclin (PGI2; epoprostenol). The platelet anti-aggregating and cardiovascular effects of 9 beta Me have been compared to PGI2 in anaesthetized monkeys and dogs. In addition, their haemodynamic effects have been compared in open-chest anaesthetized dogs and conscious dogs. Intravenous infusion of 9 beta Me and PGI2 to the anaesthetized monkey resulted in a dose-dependent hypotension, tachycardia and inhibition of ex vivo ADP-induced platelet aggregation. 9 beta Me was 72 times less active than PGI2 both as a hypotensive and anti-aggregating agent. Intravenous infusion of 9 beta Me and PGI2 to the anaesthetized beagle dog resulted in a qualitatively similar haemodynamic profile. Thus both substances induced a dose-dependent hypotension accompanied initially by a slightly increased heart rate, a dose-dependent increase in cardiac output, stroke volume and an increased peak LV dP/dt. At the higher doses studied, the initial increases in the parameters measured were succeeded by dose-dependent falls. 9 beta Me was 76 times less active than PGI2 as a hypotensive agent. In the anaesthetized greyhound, a dose-dependent anti-aggregating and hypotensive effect was seen with either drug, with 9 beta Me being 23 and 40 times less active than PGI2, respectively. Intravenous infusion of 9 beta Me and PGI2 to the conscious beagle dog induced a dose-dependent hypotension and a variable effect on heart rate. 9 beta Me was 33 times less active than PGI2 as an hypotensive agent. The duration of the hypotensive response induced by 9PMe was not significantly different from that induced by PGI2 in either monkey or beagle dog.

BW A575C: pharmacological profile in vivo of a novel angiotensin converting enzyme inhibitor and beta-blocker.

The novel compound BW A575C, N-(1-(S)-carboxy-5-[4-(3-isopropylamino-2-(R,S)-hydroxypropoxy)-indole-2 - carboxamido]pentyl)-(R,S)-alanyl-(S)-proline, is a potent angiotensin converting enzyme (ACE) inhibitor and beta-blocker in vitro. It was therefore of considerable interest to establish whether this novel pharmacological profile was maintained in vivo. In conscious instrumented normotensive rats and dogs, intravenous and oral administration of BW A575C causes a dose-dependent rightward displacement of the pressor dose-response curve to angiotensin I (dose ratio of 29.5 and 16.1 in rats and dogs, respectively, at 1.0 mg/kg i.v.) and the tachycardia dose-response curve to isoprenaline (dose ratio of 3.1 and 8.0 in rats and dogs, respectively, at 1.0 mg/kg i.v.). In these experiments BW A575C is approximately 2-10 times more active as an ACE inhibitor than as a beta-blocker. In conscious instrumented acute renovascular hypertensive dogs, where plasma renin activity is elevated 10-fold, BW A575C (1.0 mg/kg i.v.) causes a reduction in blood pressure of 35% within 10 min of injection, which is sustained for up to 4 h. This reduction in blood pressure is accompanied by a consistent, but nonsignificant, reduction in heart rate. These results confirm the novel pharmacological profile of BW A575C in vivo and demonstrate that this compound is an effective antihypertensive agent in a renin-dependent model of hypertension.

Doxantrazole, an antiallergic agent orally effective in man.

In-vivo studies have demonstrated antiallergic properties in doxantrazole when given orally to rats. These properties were confirmed in work with in-vitro preparations. No significant animal toxicity has been detected. 200 mg. given by mouth inhibited the immediate-type asthmatic response in volunteer patients challenged with specific antigen.