Ischaemically induced alterations in electrical activity and mechanical performance of isolated blood perfused canine myocardial preparations.

STUDY OBJECTIVE: The aim was to investigate the direct effect of ischaemic insult on the electrical activity or mechanical performance of the sinoatrial node, atrioventricular node or Purkinje fibres (ventricular papillary muscle) of the dog heart. DESIGN: The three isolated tissues independently mounted in a water jacketed glass container were cross circulated through their respective arteries at a constant pressure (120 mm Hg) with arterial blood from a heparinised supporting dog under sodium pentobarbitone anaesthesia. Rate of automatic rhythmical contractions (automaticity) or tension development was measured before, during, and after ischaemia (30 min). EXPERIMENTAL PREPARATIONS: Seven sinoatrial nodes, five atrioventricular nodes, and 11 papillary muscles were prepared from the heart of mongrel dogs, weighing 11.5-15 kg. MEASUREMENTS AND MAIN RESULTS: The automaticity of the sinoatrial node and atrioventricular node exhibited a high degree of resistance to ischaemia, whereas both the automaticity (Purkinje fibres) and the tension development of papillary muscle were more susceptible to ischaemia and ultimately disappeared during ischaemia. Upon resumption of the blood supply, contractility rapidly returned to preischaemic levels. However, force-frequency analyses revealed that even after reperfusion, papillary muscle had lost the ability to respond normally to stimulus frequencies greater than 2 Hz. CONCLUSIONS: The findings suggest (1) that in the special excitatory and conductive system, the more distal the segment is to the sinoatrial node, the more vulnerable it is to ischaemia; (2) that the myocardium impaired by ischaemic insult lacks functional reserve, as evidenced by enlargement of the differences between the alternate tensions of pulsus alternans; and (3) that cessation of the blood supply does not predominantly damage those tissues whose functions are mainly regulated by a slow inward calcium current.

Cerebral ischemia decreases the behavioral effects and mortality rate elicited by activation of NMDA receptors in mice.

The purpose of this study was to determine whether prior transient cerebral ischemia, in conscious mice, would alter the biological responses resulting from excessive activation of N-methyl-D-aspartate (NMDA) receptors, in an early stage. The responses to the activation of NMDA receptors by an intracerebroventricular injection of NMDA, such as wild running, tonic and clonic convulsions, absence of the visual placing reflex, loss of the righting reflex, impaired motor function and a high mortality rate, were to a large extent prevented if 30 min before treatment, either a 10-min period of global cerebral ischemia was induced or a 1 nmol intraventricular injection of NMDA was given but not if either of the above procedures was done one day before the test dose of NMDA. In contrast, behavioral symptoms, in response to activation of non-NMDA-type glutamate receptors elicited by intraventricular injection of either kainic acid or AMPA, were not clearly affected. Transient systemic hypercapnic anoxia (22-sec exposure to 100% CO2 gas), before treatment with NMDA did not significantly reduce the NMDA-induced behavior. The severity of these behavioral responses and high mortality rate observed after intraventricular injection of pentylenetetrazole (PTZ, 30 mumol) were not altered by either prior global ischemic insult or by a preexposure to NMDA given intraventricularly. The NMDA antagonist, MK801 (0.1 and 0.3 mg/kg i.p.) greatly reduced the behavioral effects and mortality rate, resulting from the intraventricular injection of NMDA and somewhat reduced the effects of the intraventricular injection of PTZ.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of the calcium-antagonistic vasodilators, nifedipine and verapamil, on the tracheal musculature and vasculature of the dog.

In anaesthetized dogs the trachea in situ was perfused arterially with blood, and drugs were injected intraarterially. Isoprenaline and the calcium-antagonistic vasodilators, nifedipine and verapamil, increased tracheal blood flow and decreased resting tone of the trachea. Isoprenaline was equi-effective in producing tracheal vasodilatation and tracheal dilatation. The two calcium-antagonistic vasodilators were less effective tracheal dilators than tracheal vasodilators.

Pharmacological analysis of histamine receptors in musculature and vasculature of the dog trachea in situ.

1 The role of histamine H1- and H2-receptors in the musculature and vasculature of the dog trachea was investigated in the blood-perfused trachea in situ. 2 Histamine and acetylcholine caused increases in blood flow (tracheal, vasodilatation) and in intraluminal pressure (tracheal constriction) in a dose-dependent manner. Histamine was almost equipotent to acetylcholine in causing tracheal vasodilatation but was about 30 times less potent in causing tracheal constriction. 3 The histamine H2-receptor agonist, dimaprit, caused a dose-dependent increase in tracheal blood flow but failed to cause tracheal constriction. 4 The tracheal constriction produced by histamine was inhibited strongly by diphenhydramine but not modifed by metiamide. The tracheal vasodilatation produced by histamine was antagonized by both diphenhydramine and metiamide; diphenhydramine was more effective than metiamide. 5 It is concluded that in the tracheal musculature, histamine receptors are exclusively of the H1-type and mediate constriction, whereas in the tracheal vasculature, both histamine H1- and H2-receptors mediate vasodilatation but histamine H1-receptors are predominant.

A method for recording smooth muscle and vascular responses of the blood-perfused dog trachea in situ.

1 A method is described for measuring responses of dog tracheal musculature and vasculature in situ. 2 The upper two thirds of the trachea was perfused with blood through both cranial thyroid arteries at a constant pressure. The blood flow through the arteries was measured with an electromagnetic flowmeter. The response of the tracheal musculature was measured as a change in pressure in a water-filled cuff inserted into the trachea via the mouth. Drugs were injected close-arterially. 3 Acetylcholine produced dose-dependent increases in blood flow rate (vasodilatation) and in tracheal intraluminal pressure (tracheal constriction). These responses were antagonized by atropine. 4 Isoprenaline produced vasodilatation which was blocked by propranolol. Adrenaline and noradrenaline caused vasocontriction which was blocked by phentolamine. 5 All three catecholamines produced a decrease in tracheal intraluminal pressure (tracheal dilatation). The tracheal dilatation in response to adrenaline and noradrenaline was converted to constriction by propranolol. The tracheal constriction thus unmasked was abolished specifically by phentolamine. 6 From these results it is concluded that the tracheal musculature and vasculature contain muscarinic receptors, and excitatory alpha- and inhibitory beta-adrenoceptors. In the tracheal musculature beta-adrenoceptors predominate over alpha-adrenoceptors; the reverse is true in the tracheal vasculature.

Assessment of the selectivity of OPC-2009, a new beta2-adrenoceptor stimulatn, by the use of the blood-perfused trachea in situ and of the isolated blood-perfused papillary muscle of the dog.

1 The potency and selectivity of 5-(1-hydroxy-2-isopropylamino)butyl-8-hydroxy carbostyril hydrochloride hemihydrate (OPC-2009), a new beta(2)-adrenoceptor stimulant, was compared with those of isoprenaline, trimetoquinol and salbutamol by the use of blood-perfused tracheal preparations in situ and of blood-perfused papillary muscle preparations of the dog. All drugs were injected intra-arterially.2 All the four drugs decreased tracheal intraluminal pressure (tracheal relaxation) and increased tracheal blood flow in a dose-dependent manner. The four drugs produced a dose-dependent increase in developed tension of papillary muscles. In both preparations the duration of action of isoprenaline and salbutamol was short, whereas that of OPC-2009 and trimetoquinol was long. These effects were antagonized by propranolol.3 Dose-response curves to the four drugs for tracheal relaxation were almost parallel. OPC-2009 was 2.4 times more potent, and trimetoquinol and salbutamol were 2.2 and 6.2 times less potent than isoprenaline in causing tracheal relaxation.4 Dose-response curves to the four drugs for tracheal vasodilatation were also parallel. OPC-2009, trimetoquinol and salbutamol were 3.9, 6.7 and 23 times less potent than isoprenaline.5 Slopes of the dose-response curves to the four drugs for increased developed tension were not parallel; that of OPC-2009 was the least steep, whereas that of isoprenaline was the steepest. Trimetoquinol, salbutamol and OPC-2009 were about 18, 570 and 2400 times less potent than isoprenaline.6 Selectivity calculated from relative potencies indicate that OPC-2009 was about 6000 times, salbutamol about 92 times and trimetoquinol about 8.2 times more selective than isoprenaline for tracheal smooth muscle as compared to ventricular muscle.7 The high potency and selectivity of OPC-2009 for tracheal smooth muscle and its long duration of action suggest its potential usefulness for treatment of bronchial asthma.8 The present results are also compatible with the concept that beta(1)-adrenoceptors in cardiac muscle and beta(2)-adrenoceptors in tracheal and vascular smooth muscle can be distinguished. Furthermore, the results revealed that the beta-adrenoceptors mediating tracheal relaxation and vasodilatation may also be different.

Dextrorphan attenuates the behavioral consequences of ischemia and the biochemical consequences of anoxia: possible role of N-methyl-d-aspartate receptor antagonism and ATP replenishing action in its cerebroprotecting profile.

The acute anti-ischemic and anti-anoxic effects of dextrorphan (DX) were compared with those of dizocilpine (MK-801) in a variety of animal models, and in vivo and in vitro testings under anoxic conditions. DX reduced the incidence of death in ischemic mice and improved the rotarod performance of mice with brain ischemia. The ischemically-impaired memory of mice treated with DX markedly improved, as shown in the step-through type passive avoidance test, Morris water maze and in the habituation of exploratory behavior test. MK-801 likewise improved the water maze performance of the ischemically-impaired mice, but to a lesser extent. The step-through type passive avoidance performance of ischemic mice was not improved by MK-801. In the passive avoidance task with normal mice, DX, like MK-801, produced anterograde amnesia at doses higher than those needed to attenuate the behavioral effects of ischemia. DX, intravenously or centrally administered, markedly and dose-dependently reduced the incidence of death in mice receiving potassium cyanide (KCN). DX lessened the reduction in adenosine triphosphate (ATP) and increased lactate contents in mice dosed with KCN and also lessened the reduction in ATP in the TCA cycle and oxidative phosphorylation reactions caused by KCN (0.58 mmol/l), whereas MK-801 failed to show any effect on ATP formation pathways in vivo and in vitro, and failed to protect mice against KCN-induced lethal toxicity in vivo. In the in vitro studies, DX increased the adenylate kinase activity of the rat brain homogenate. DX was found to be a cerebroprotectant with anti-ischemic and anti-anoxic actions, the effects probably stemming from its N-methyl-d-aspartate receptor antagonistic property in cooperation with its ATP replenishing action.

Effects of CCK antagonists on CCK-induced suppression of locomotor activity in mice.

Sulfated cholecystokinin octapeptide (CCK-8) was administered either intraperitoneally or into the cerebral ventricle of fully conscious mice, and locomotor activity was quantified. CCK-8 administered by either route suppressed locomotor activity. Subcutaneously administered selective CCK-A receptor antagonist, L-364,718 (1 mg/kg), reversed the inhibitory effect of centrally as well as peripherally administered CCK-8, but the selective CCK-B receptor antagonist, L-365,260 (1 mg/kg), did not. These results demonstrate that centrally as well as peripherally administered CCK-8 suppresses locomotor activity in mice through an interaction with CCK-A, but not CCK-B, receptors.

Analysis of the vasodilator action of alprenolol.

The effect of alprenolol and other beta-adrenoceptor antagonists, including d-isomers, on blood flow in femoral, coronary and mesenteric vascular beds was measured in anesthetized dogs. Under conditions of constant perfusion pressure, intra-arterial injection of beta-adrenoceptor antagonists produced vasodilation. Propranolol and alprenolol were approximately equipotent in coronary and mesenteric beds but alprenolol was significantly more potent in the femoral bed. Practolol was virtually inactive in all beds. The vasodilating potency of d-alprenolol and d-propranolol was not significantly different from that of the respective racemic mixtures. The vasodilator response to alprenolol was not affected by pretreatment with atropine, diphenhydramine or propranolol. In conscious normotensive dogs i.v. injections of d,l- and d-alprenolol produced dose-dependent decreases in blood pressure and increases in heart rate. Under similar conditions, i.v. d,l-propranolol was without effect on either measurement. The results suggest that the hypotensive action of alprenolol in dogs may derive from its vasodilator activity.

Effects of hexoestrol on the contractility of the isolated, blood-perfused canine papillary muscle and of the guinea-pig ileum.

The effects of hexoestrol were studied on the blood flow and the tension development of the isolated, blood-perfused papillary muscle of the dog, as well as on the contractions of the guinea-pig ileum induced by acetylcholine, histamine or BaCl2. Hexoestrol caused an increase in coronary blood flow and a negative inotropic effect in a dose-dependent manner. High doses of hexoestrol produced a loss of contractility of the papillary muscle without significant alterations of the amplitude and shape of the electrical activity recorded extracellularly. Hexoestrol had a strong non-selective relaxant effect on the guinea-pig ileum and was 10-20 times more potent than papaverine in antagonizing contractions induced by the 3 agonists. These results indicate that hexoestrol probably acts by blocking certain steps in the process by which extracellular and/or superficially bound Ca ions move to the contractile machinery in cardiac and in smooth muscle cells. Thus, it may bear some resemblance to the so-called calcium antagonists.