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J R Parratt

Publications and source records attributed to J R Parratt.

At least 19 recordsLinked to original sources
PubMed1992

Acid optimum kininogenases in canine myocardium and aorta.

OBJECTIVE: Canine coronary artery was recently reported to contain a cathepsin like acid optimum enzyme and a kallikrein like alkaline optimum enzyme which cleaved from a crude kininogen preparation a vasodilator uterus contracting substance. The aim of this study was to seek the presence of similar acid optimum enzymes in canine ventricular myocardium and in a large systemic artery, the aorta. METHODS: Aqueous canine tissue extracts were tested for the ability at different pHs to release uterus contracting substance (using rat isolated oestrous uterus) from a kininogen preparation. After gel filtration, the extracts were tested for the presence of arginine-amidase activity (substrate: D-Val.Leu.Arg.pNA) and enzymic activity forming bradykinin like immunoreactivity. Tissues were obtained from anaesthetised greyhounds which had been used in control studies and had received no other drug treatment. RESULTS: Ventricular extracts released uterus contracting substance optimally at pH 5.2-5.4, but not at alkaline pH, neither was bradykinin like immunoreactivity formed at alkaline pH. Inhibitor studies and gel filtration showed this activity to be due to a cathepsin-D-like enzyme, molecular weight (MW) 42.6 (SD 0.9) kd, which was an arginine amidase and released bradykinin like immunoreactivity from a plasma kininogen. Aortic extracts showed two pH related peaks of uterus contracting substance formation, at pH 5.2 and (unlike myocardium) at pH 8. Also unlike myocardium, aortic extracts gave two acid optimum kininogenase peaks on gel filtration, with MW 42(4.6) kd and 252(39) kd, respectively. Both peaks released bradykinin like immunoreactivity. CONCLUSIONS: Canine aorta contained an alkaline optimum and two acid optimum enzymes, while ventricle contained only a cathepsin-D-like acid optimum enzyme, all of which could form bradykinin like immunoreactivity. The ability of the ventricular enzyme to form a kinin in the slightly acid conditions of myocardial ischaemia may have a protective role.

Animals↗
PubMed1992

Antiarrhythmic effects of preconditioning in anaesthetised dogs and rats.

OBJECTIVE: The aim was to determine the relationship of the duration of short coronary artery occlusions and of the reperfusion period to the extent of the antiarrhythmic effect of preconditioning. METHODS: A prolonged occlusion of a coronary artery in 102 anaesthetised rats and 55 anaesthetised dogs was preceded by a variable number of preconditioning coronary artery occlusions, of varying duration and with variable reperfusion periods between them and the prolonged occlusion. RESULTS: Preconditioning in both species reduced the severity of ischaemia induced arrhythmias, epicardial ST segment changes, and alterations in the degree of inhomogeneity of conduction during a subsequent prolonged coronary artery occlusion, provided that the reperfusion time was less than 30 min (in rats) and 1 h (in dogs). This antiarrhythmic effect of preconditioning was marked; eg, in dogs following two preconditioning occlusions survival from a combined ischaemia-reperfusion insult was 40% (cf, 0% in the controls). CONCLUSIONS: Short preconditioning periods of myocardial ischaemia protect the myocardium against the arrhythmogenic effects of a more prolonged occlusion. The optimum time for this preconditioning occlusion in rats is 3 min and protection is still apparent 30 min later. In dogs, the protective effect is especially clear with two short (5 min) coronary artery occlusions. The protection in this species lasts for less than 1 h.

Animals↗
PubMed1991

Endotoxin-induced impairment of vasodepressor responses in the pithed rat.

The effects of Eschericia coli endotoxin on vascular responsiveness were compared with those of sodium nitroprusside in pithed rats. Infusion of endotoxin (250 micrograms kg-1 h-1) produced a fall in mean arterial blood pressure (11 mmHg) and impaired vasodepressor responses to endothelin, 5-hydroxytryptamine, acetylcholine, bradykinin, sodium nitroprusside and salbutamol. Prevention of endotoxin-induced hypotension with vasopressin infusion (0.64 i.u. kg-1 h-1 i.v.) restored responsiveness to bradykinin, tended to restore responsiveness to endothelin and sodium nitroprusside but failed to restore responsiveness to acetylcholine, 5-HT or salbutamol. Infusion of sodium nitroprusside at a rate (400 micrograms kg-1 h-1) producing a similar fall in blood pressure to that produced by endotoxin markedly impaired vasodepressor responsiveness to 5-HT. However, this was fully restored when the hypotension was prevented by vasopressin infusion. Vasodepressor responsiveness to either acetylcholine or salbutamol was not impaired by sodium nitroprusside in vasopressin-infused rats. The impairment of vasodepressor responsiveness by endotoxin is not due to endotoxin-induced hypotension and does not fit clearly with an endotoxin-mediated impairment of endothelial function.

Acetylcholine↗
PubMed1991

Endotoxin impairs the response of rat anococcygeus muscle to electrical field stimulation.

Rat anococcygeus muscles were isolated 4 h after treatment with either E. coli endotoxin (20 mg kg-1 i.p.) or saline. The contractile responses of the muscle to electrical field stimulation, and to the alpha 1-adrenoceptor agonist cirazoline were impaired by endotoxin treatment. Inhibition of the L-arginine pathway with L-NG-nitro arginine methylester (3 x 10(-5) M) failed to restore responsiveness to either electrical field stimulation or to cirazoline. Endotoxin impaired inhibitory responses to electrical field stimulation in preparations precontracted with cirazoline. Responsiveness to sodium nitroprusside was also impaired by endotoxin under these conditions. These results show an impairment by endotoxin of both contractile and inhibitory responses of the rat anococcygeus muscle to electrical field stimulation. The impairment appears to be post-junctional. In contrast to the findings in vascular smooth muscle, the endotoxin-induced impairment of contractile responses does not appear to involve the L-arginine pathway.

Adrenergic alpha-Agonists↗
PubMed1991

Transient ischaemia induced by rapid cardiac pacing results in myocardial preconditioning.

STUDY OBJECTIVE: The aim was to determine whether rapid ventricular pacing can protect against the ventricular arrhythmias occurring during a subsequent coronary artery occlusion. DESIGN: The effect was examined of two 2 min periods of pacing (300 beats.min-1) in chloralose-urethane anaesthetised dogs on a subsequent 25 min coronary artery occlusion. Ventricular arrhythmias, ST segment elevation, and inhomogeneity of conduction were analysed. EXPERIMENTAL MATERIAL: 25 anaesthetised mongrel dogs in a restricted body weight range were used. MEASUREMENTS AND MAIN RESULTS: Preocclusion pacing reduced the severity of occlusion induced ST segment elevation, degree of inhomogeneity, and arrhythmias: ventricular premature beats were reduced from 528(SEM 40) to 136(45), and there were lower incidences of ventricular fibrillation (0% v 47%) and ventricular tachycardia (30% v 80%). CONCLUSIONS: Rapid ventricular pacing "preconditions" the myocardium in a manner similar to that following short coronary artery occlusions. Short periods of ischaemia no matter how induced protect the heart against the arrhythmogenic effect of a prolonged coronary artery occlusion.

Animals↗
PubMed1991

Failure of cyclo-oxygenase inhibition to protect against arrhythmias induced by ischaemia and reperfusion: implications for the role of prostaglandins as endogenous myocardial protective substances.

STUDY OBJECTIVE: It has been suggested that the balance between the release from the heart of prostacyclin and thromboxane A2 is a major determinant of the severity of arrhythmias during ischaemia and reperfusion. This has been examined in a dog model. DESIGN: Three different cyclo-oxygenase inhibitors in doses adequate to prevent formation of both prostacyclin and thromboxane--aspirin (7 mg.kg-1), flurbiprofen (3 mg.kg-1), and sodium meclofenamate (2 mg.kg-1) with or without nafazatrom or dazmegrel--were given prior to a combined occlusion-reperfusion insult, and the severity of resulting arrhythmias examined. MATERIAL: Adult greyhound dogs were used: controls n = 29; aspirin n = 10; flurbiprofen n = 10; sodium meclofenamate +/- nafazatrom or dazmegrel n = 22. MEASUREMENTS AND MAIN RESULTS: None of the interventions modified the severity of ischaemic arrhythmias induced by coronary artery occlusion and release. The numbers of ventricular extrasystoles during the 40 min occlusion period were similar in all groups: controls 653(SEM 109); aspirin 690(187); flurbiprofen 454(132); meclofenamate 833(218). Ventricular fibrillation from the combined occlusion-reperfusion insult was also similar; controls 83%; aspirin 80%; flurbiprofen 80%; meclofenamate 100%. In the doses used all three inhibitors prevented the increase in plasma concentrations of thromboxane A2 [from 104(23) to 166(34) pg.ml-1] and prostacyclin [from 450(80) to 720(110) pg.ml-1] seen in control untreated dogs subjected to coronary artery occlusion. The addition of sodium meclofenamate to either nafazatrom (10 mg.kg-1 orally) or dazmegrel (3 mg.kg-1 intravenously), which when given alone are markedly protective, abolished this protection. CONCLUSION: The results show the importance of maintaining prostacyclin release in modifying the severity of ischaemic and reperfusion arrhythmias, and again suggest that prostacyclin is an "endogenous antiarrhythmic substance".

Animals↗
PubMed1991

Evidence that an L-arginine/nitric oxide dependent elevation of tissue cyclic GMP content is involved in depression of vascular reactivity by endotoxin.

1. The aim of this investigation was to study the relationship between contractile responsiveness, activation of the L-arginine pathway and tissue levels of guanosine 3':5'cyclic monophosphate (cylic GMP) in aortic rings removed from rats 4 h after intraperitoneal administration of bacterial endotoxin (E. coli. lipopolysaccharide, LPS, 20 mg kg-1). 2. LPS-treatment resulted in a reduction of the sensitivity and maximal contractile response to noradrenaline (NA). 3. Depression of the maximal contractile response was restored to control by 6-anilo-5,8-quinolinedione (LY 83583, 10 microM), which prevents activation of soluble guanylate cyclase. 4. Cyclic GMP levels in tissue from LPS-treated rats were 2 fold greater than cyclic GMP levels detected in tissue from control (saline-treated) rats. The LPS-induced increase in cyclic GMP content was observed both in the presence and absence of functional endothelium. 5. Addition of L-arginine 1 mM) to maximally contracted aortic rings produced significantly relaxation of rings from LPS-treated rats but not rings from control animals. In the LPS-treated group, addition of L-arginine was also associated with a significant increase in cyclic GMP content. L-Arginine had no effect on the cyclic GMP content of control rings. D-Arginine (1 mM) was without effect. 6. In rings from LPS-treated rats, NG-nitro-L-arginine methyl ester (L-NAME, 300 microM), an inhibitor of nitric oxide (NO) production, increased the contractile response to NA and prevented the LPS-induced increase in cyclic GMP content. In control rings, L-NAME increased the NA sensitivity only when the endothelium remained intact and reduced the cyclic GMP content of these rings to that of control endothelium-denuded rings. 7. These results demonstrate that LPS-induced hyporeactivity to NA occurs secondarily to activation of the L-arginine pathway and subsequent activation of soluble guanylate cyclase in vascular tissue. In addition they suggest that LPS induces the production of an NO-like relaxing factor in non-endothelial cells.

Aminoquinolines↗
PubMed1991

The effect of inhibitors of the L-arginine/nitric oxide pathway on endotoxin-induced loss of vascular responsiveness in anaesthetized rats.

1. The effects on blood pressure and on pressor responses to noradrenaline (NA), of NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME), inhibitors of the L-arginine/nitric oxide pathway, were investigated in anaesthetized rats receiving an infusion of bacterial endotoxin (E. coli lipopolysaccharide, LPS). 2. Infusion of LPS (10 mg kg-1 h-1) for 50 min had no effect on mean arterial blood pressure (MABP) but induced a reduction in responsiveness to noradrenaline (100 ng-1 micrograms kg-1). L-NMMA (30 mg kg-1), but not D-NMMA, caused an increase in MABP of approximately 30 mmHg and restored responses to NA. This effect was reversed by L- but not D-arginine (100 mg kg-1). 3. In LPS-treated rats, blood pressure responses to NA were only marginally increased by the cyclooxygenase inhibitor, indomethacin (5 mg kg-1). L-NAME (1 mg kg-1) caused a similar increase in MABP and restored pressor responses to NA both in the presence and absence of indomethacin. 4. Co-infusion of vasopressin (100 ng kg-1, for 10 min) with LPS (10 mg kg-1 h-1) in order to reproduce the hypertensive effect of L-NMMA and L-NAME increased pressor responsiveness to 100 and 300 ng kg-1 NA but not to 1 microgram kg-1 NA. 5. Infusion of sodium nitroprusside (30 micrograms kg-1 min-1) decreased responsiveness to NA even when the hypotension was corrected by co-infusion of vasopressin (50 ng kg-1 min-1). 6. These results demonstrate that the restoration of vascular responsiveness to NA in LPS-treated anaesthetized rats by inhibitors of the L-arginine/nitric oxide pathway is stereospecific and reversible. Furthermore, the experiments involving indomethacin suggest that although cyclo-oxygenase products of arachidonic acid may contribute to the development of LPS-induced hyporeactivity, the effect of L-NAME is unlikely to involve inhibition of the cyclo-oxygenase pathway. Comparison of NA responsiveness during vasopressin and L-NMMA/L-NAME-induced hypertension shows that increasing the blood pressure may modify LPS-induced hyporeactivity, but cannot account for the complete restoration of responses to NA by L-NMMA and L-NAME. These observations suggest that activation of nitric oxide formation from L-arginine makes a direct contribution to the production of vascular hyporeactivity by LPS in vivo.

Animals↗
PubMed1991

Local intracoronary infusions of bradykinin profoundly reduce the severity of ischaemia-induced arrhythmias in anaesthetized dogs.

Bradykinin in a dose (25 ng kg-1 min-1) which did not alter coronary flow, or saline, were infused into a small branch of the left anterior descending coronary artery in dogs anaesthetized with chloralose and urethane, for 10 min prior to coronary artery occlusion and throughout the 25 min occlusion period. The degree of inhomogeneity of conduction and epicardial ST-segment changes were measured in the ischaemic zone with a composite electrode. In control dogs, coronary artery occlusion led to severe arrhythmias with an incidence of ventricular fibrillation of 47% and tachycardia of 80% and with a mean of 528 +/- 140 ventricular premature beats. In marked contrast, those dogs administered bradykinin had no ventricular fibrillation or tachycardia and the number of premature beats was significantly less (53 +/- 19). ST-segment changes were also much less in these dogs. These results raise the possibility that bradykinin might contribute to the protective effects of preconditioning and acts as an 'endogenous myocardial protective substance'.

Anesthetics↗
PubMed1990

An L-arginine-derived factor mediates endotoxin-induced vascular hyposensitivity to calcium.

Aortas removed from rats treated with bacterial endotoxin displayed a reduced sensitivity to calcium (CaCl2, 10 microM-10 mM) in depolarizing medium (100 mM K+). Sensitivity was reduced further in the presence of L-arginine (1 mM) but restored to control by N omega-nitroarginine methyl ester (L-NAME, 300 microM) or NG-monomethyl-L-arginine (L-NMMA, 300 microM), inhibitors of nitric oxide synthesis from L-arginine. Furthermore, addition of methylene blue (10 microM), an inhibitor of soluble guanylate cyclase, restored the contractile response to 10 mM CaCl2. The results suggest that vascular hyposensitivity to calcium involves stimulation of guanylate cyclase subsequent to activation of the L-arginine pathway by endotoxin.

Animals↗
PubMed1990

Endotoxin-induced impairment of vascular smooth muscle contractions elicited by different mechanisms.

The current study was designed to analyse the mechanisms which are impaired in the vascular hyporeactivity to contractile agents induced by E. coli lipopolysaccharide endotoxin (LPS). Endothelium-denuded aortic rings were prepared from thoracic aorta removed from control and LPS-pretreated rats (20 mg/kg i.p., 4 h before the experiment). In order to determine whether LPS treatment altered the contractile components that depend on intracellular calcium release and extracellular calcium entry to the same extent, rings were contracted under various experimental conditions. The responses elicited by indanidine, phenylephrine (without and with nitrendipine 1 microM), (-) Bay K 8644, (+) S 202-791 and the calcium ionophore calimycin in the presence of 1.25 mM external CaCl2 were all impaired by LPS pretreatment (maximal contractions 19, 63, 44, 28, 22 and 22% of controls, respectively). Concentration-effect curves for CaCl2 made in depolarizing medium (KCl 40 and 100 mM) and in the presence of calimycin (3 microM) were shifted to the right in rings from LPS-pretreated rats. However, the LPS-induced depression of contraction was overcome by the addition of CaCl2 (up to 30 mM). Additionally, in the absence of external CaCl2, the contraction induced by caffeine (50 mM) was not significantly altered by LPS treatment. It is concluded that LPS treatment does not reduce the ability of aortic smooth muscle cells to contract. The results suggest that LPS treatment impairs mechanisms involved in calcium handling within smooth muscle cells after stimulation of calcium entry through different pathways and activation of intracellular calcium release by alpha 1-adrenoceptor agonists.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

Incubation with endotoxin activates the L-arginine pathway in vascular tissue.

Rat aortic rings incubated with a low dose of endotoxin (100 ng ml-1) for 5 h exhibited depressed reactivity to norepinephrine (NE) which was independent of the presence of endothelium. An inhibitor of nitric oxide synthesis from L-arginine NGmonomethyl-L-arginine (300 microM), but not the inactive D-enantiomer, restored the contractile response of endotoxin-treated rings to control. The effect of NGmonomethyl-L-arginine was reversed by L-arginine (1 mM). In the absence of NGmonomethyl-L-arginine, L- but not D-arginine relaxed endotoxin-treated rings but was without effect on control tissues. This response was reversed following inhibition of guanylate cyclase by methylene blue (3 microM). In addition, tissue cyclic GMP content was 10 times greater in endotoxin-treated compared to control tissue. These data indicate that endotoxin can act directly on vascular tissue to induce a hyporeactivity to NE which is secondary to the activation of the L-arginine pathway and subsequent activation of soluble guanylate cyclase.

Animals↗
PubMed1990

Protective effects of preconditioning of the ischaemic myocardium involve cyclo-oxygenase products.

STUDY OBJECTIVE: The aim was to determine whether short (preconditioning) occlusions of a coronary artery protect against the arrhythmias occurring during a subsequent more prolonged occlusion and to examine whether the observed protection is mediated by the release of a product of the cyclo-oxygenase pathway of arachidonic acid metabolism. DESIGN: The effects were examined of two short (5 min) coronary artery occlusions, in chloralose-urethane anaesthetised dogs, on a subsequent prolonged (25 min) occlusion; analysis of ischaemia and reperfusion induced arrhythmias and of epicardial ST segment changes was performed. EXPERIMENTAL MATERIAL: 46 anaesthetised mongrel dogs in a restricted body weight range were used. MEASUREMENTS AND MAIN RESULTS: Preconditioning reduced the incidence and severity of ischaemic arrhythmias during a 25 min occlusion. Ventricular premature beats (VPB) reduced from 445 (SEM 140) to 96(22) (p less than 0.01), ventricular fibrillation (VF) from 4/10 to 0/20 (p less than 0.05), and ventricular tachycardia from 9/10 to 6/20 (p less than 0.05). VF following reperfusion was reduced from 6/6 to 6/10 (p less than 0.05). Preconditioning thus increased survival from the prolonged ischaemia-reperfusion insult from 0% to 40%. The protective effect of preconditioning was lost in the presence of the cyclo-oxygenase inhibitor sodium meclofenamate (2 mg.kg-1), eg, VPBs 367(95), VF during occlusion 1/9 and during reperfusion 8/8, survival 0%. CONCLUSIONS: Short, preconditioning periods of myocardial ischaemia protect the myocardium against the arrhythmogenic effects of a more prolonged occlusion. That this protection is lost if the cyclo-oxygenase pathway is blocked suggests a protective role for prostanoids, most likely prostacyclin, as endogenous myocardial protective substances.

Animals↗
PubMed1990

Endotoxin-induced impairment of vasopressor and vasodepressor responses in the pithed rat.

1. Effects of E. coli endotoxin on vascular responsiveness to a variety of agents were compared with those of the calcium channel blocking drug nicardipine in pithed rats. 2. Infusion of endotoxin (250 micrograms kg-1 h-1) produced a fall in mean arterial blood pressure (8 mmHg). A similar fall (11 mmHg) was seen in rats receiving nicardipine (1.0 mg kg-1). 3. Endotoxin impaired responsiveness to vasopressin, phenylephrine and cirazoline, producing a shift to the right in the dose-response curves without any change in the maximum response. Responsiveness to 5-hydroxytryptamine (5-HT) and to the alpha 2-adrenoceptor agonists clonidine and BHT 933, was also impaired with a marked reduction in their maximum responses. The dose-response curve to the pressor effects of endothelin was not significantly modified. 4. Nicardipine produced a similar pattern of impairment of responsiveness to these agents to that produced by endotoxin. However, nicardipine also shifted the pressor dose-response curve to endothelin to the right with no significant alteration in its maximum response. 5. The pressor responses to endothelin and to 5-HT were, respectively, preceded and followed by dose-dependent depressor responses, which were markedly reduced by endotoxin and nicardipine. 6. The concomitant infusion of arginine vasopressin (0.64 iu kg-1 h-1) prevented endotoxin-induced hypotension and also prevented the impairment in responsiveness to cirazoline and to BHT 933. 7. The similarity of the pattern of impaired pressor responsiveness (except in relation to endothelin) and depressor responsiveness produced by endotoxin and nicardipine may be consistent with a common mechanism of action.

Animals↗
PubMed1990

Loss of vascular responsiveness induced by endotoxin involves L-arginine pathway.

The involvement of L-arginine-dependent nitric oxide (NO) production in the vascular failure observed in endotoxemia was investigated in male Wistar rats treated with Escherichia coli lipopolysaccharide (LPS). Contractile responses to norepinephrine (NE) were measured ex vivo in aortas isolated from rats treated with LPS (20 mg/kg ip, 4 h before experiments) and pressor responses to NE were recorded in vivo in rats infused with LPS (5 mg.kg-1.h-1 iv). LPS pretreatment induced a rightward shift of the concentration-response curve to NE and a reduction of the maximal contraction by approximately 43% and 54% (P less than 0.05) in aortic rings with and without functional endothelium, respectively. This was not modified by the presence of indomethacin (10 microM) during the contractile experiments. In contrast, in the presence of NG-monomethyl-L-arginine (L-NMMA, 300 microM) or methylene blue (10 microM), maximal contractions to NE were restored to control values whether functional endothelium was present or not. The effects of L-NMMA were reversed by L- but not by D-arginine. Additionally, the effects of LPS pretreatment on vascular contractility were potentiated by L-arginine. In vivo, LPS infusion produced a reduction in pressor responsiveness to NE (0.1-10 mg/kg), which was also abolished by L-NMMA (30 mg/kg iv). This effect of L-NMMA was reversed by L- but not by D-arginine (100 mg/kg iv). These results demonstrate that activation of the L-arginine pathway has a major role in the production of vascular hyporeactivity in endotoxemia, ex vivo as well as in vivo. Additionally, they suggest that endothelium-independent vascular production of NO may be involved.

Acetylcholine↗
PubMed1990

Endotoxin-induced impairment of vascular reactivity in the pithed rat: role of arachidonic acid metabolites.

The effect of endotoxin on vascular reactivity was studied in pithed rats. Endotoxin infusion (1 mg kg-1 h-1) impaired pressor responses to noradrenaline, angiotensin II, BAY K 8644, and stimulation of the spinal sympathetic outflow. The loss of reactivity was prevented by pretreatment with the cyclooxygenase inhibitor flurbiprofen or the dual cyclooxygenase/lipoxygenase inhibitor BW755C. The effect of endotoxin in impairing vascular reactivity to noradrenaline was mimicked by prostaglandin E2 and platelet-activating factor but not by the prostacyclin analogue iloprost. Platelet-activating factor also impaired responsiveness to sympathetic stimulation. These results suggest a role for cyclooxygenase products and, possibly, platelet-activating factor in endotoxin-induced impairment of vascular reactivity.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1989

Enzymes in normally perfused and ischaemic dog hearts which release a substance with kinin like activity.

The presence of amidases cleaving the tripeptide VAL.LEU.ARG.pNA, and liberating from human plasma kininogen substance(s) able to contract uterine smooth muscle and to lower blood pressure (uterus contracting and hypotensive activity), has been demonstrated in vascular and muscle tissues from normally perfused and ischaemic areas of dog hearts. Studies were carried out on blood free preparations of coronary arteries and veins and normally perfused and ischaemic ventricle. All the tissues were found to contain both acid optimum (pH 6) and alkaline optimum (pH greater than 9) enzymes forming uterus contracting substance (UCS, bioassayed on isolated uterus of rats in oestrus), the highest levels of both activities being found in arterial tissues and the least in ventricle. Enzyme levels in ischaemic or normally perfused ventricle did not differ significantly. Gel filtration (Sephacryl, S-300) of coronary artery extracts gave one peak each of acid optimum enzyme with a molecular weight of 38,300 +/- 800 daltons and alkaline optimum enzyme with a molecular weight of 92,100 +/- 4000 daltons. Both acid and alkaline enzyme fractions cleaved the tripeptide substrate with pH optima identical to those for UCS formation. The acid optimum activity, both of UCS formation and tripeptide cleavage, was inhibited by pepstatin but not by aprotinin or soybean trypsin inhibitor (SBTI). The alkaline optimum activity was inhibited by aprotinin and SBTI but not pepstatin. Both acid and alkaline optimum enzymes released a hypotensive agent from a plasma protein substrate. The molecular weight and response to inhibitors of the acid optimum enzyme were similar to a cathepsin, and those of the alkaline optimum enzyme were similar to plasma kallikrein.

Animals↗