The renin-angiotensin system, dietary salt, and increased sensitivity to noradrenaline in mesenteric vasculature preparations from renal/salt hypertensive rats.

Exogenous angiotensin II causes noradrenaline supersensitivity in rat mesenteric vasculature preparations. The noradrenaline supersensitivity of tissues from renal/salt hypertensive rats, with low plasma renin activity, is not caused by endogenous angiotensin II since it was unaffected by Sar1 Ileu8 angiotensin II. Dietary salt-loading caused a small increase in noradrenaline sensitivity.

Vascular reactivity to noradrenaline, potassium chloride, and angiotensin II in the rat perfused mesenteric vasculature preparation, during the development of renal hypertension.

The degree of reactivity to noradrenaline of the perfused mesenteric vasculature and the blood pressure of the renal hypertensive rat were correlated. Early (true) supersensitivity was demonstrated for noradrenaline and angiotensin but not for KCl. Later (apparent) hyperreactivity to all three substances was related to an elevated maximal response. The potentiating actions of endogenous angiotensin could cause the early (true) supersensitivity to noradrenaline.

The potential beneficial effect of nicardipine in a rat model of transient forebrain ischemia.

In a rat 3-day survival model of 10-minute four-vessel occlusion, halothane anesthesia was used to attenuate the ictal blood pressure elevation of the cerebral ischemic response and thereby maintain an isoelectric EEG. Selectively vulnerable regions of the brain were protected by preischemia plus postischemia maintenance treatment with the calcium entry blocker nicardipine. Compared with untreated animals, repeated doses at 500 micrograms/kg IP were markedly more effective than doses of 50 micrograms/kg. Ongoing studies demonstrate a neurocytoprotective action of nicardipine when deferred treatment is given postischemia.

The effects of the novel anti-anginal compound RS 43285 on myocardial conduction in the anaesthetized dog.

1. A pentobarbitone-anaesthetized canine model of myocardial conduction was developed to evaluate drug effects on intra-atrial (I-A), intra-ventricular (I-V) and atrioventricular (A-V) conduction parameters, both at rest and during electrical pacing of the right atrium or ventricle. Drug effects on the ability of the sino-atrial (SA) node to re-establish sinus rhythm on switching off electrical pacing were also considered. The effects of the novel anti-anginal compound RS 43285-193 ((+/-)-N-(2,6-dimethyl-phenyl)-4[2-hydroxy-3-(2-methoxyphenoxy)propyl] -1-piperazine acetamide dihydrochloride) were compared to those of the standard anti-anginal compounds nicardipine, nifedipine and verapamil. 2. In the dose range 15-7000 micrograms kg-1, RS 43285 had no significant effects on I-A, I-V or A-V conduction either at rest or during electrical pacing and did not affect the re-establishment of sinus rhythm. 3. Nicardipine had no effects on conduction parameters at resting heart rate. There were no effects on I-A or I-V conduction on electrical pacing but A-V conduction was increased at 200-500 micrograms kg-1 (with a 2:1 A-V conduction block in two out of six dogs); this was accompanied by a prolongation of the interval to reversion of sinus rhythm. 4. Nifedipine had no significant effects on I-A or I-V conduction but significantly prolonged A-V conduction at 1000 micrograms kg-1 and this dose also increased the interval to SA node recovery. 5. Verapamil did not effect I-A or I-V conduction. However, A-V conduction was affected with a significant prolongation occurring at resting heart rate at 100-400 Atg kg-' and a 2:1 A-V block in one dog at rest. During right atrial pacing verapamil significantly increased A-V conduction at 50- 400 fig kg-'. All dogs exhibited a 2:1 A-V conduction block at the highest frequency at 400 jig kg-'.

Prevention of myocardial enzyme release by ranolazine in a primate model of ischaemia with reperfusion.

In control anaesthetized baboons subjected to 30 min occlusion of the left anterior descending coronary artery, followed by 5.5 h reperfusion, total plasma levels for creatine kinase (CK) and lactate dehydrogenase (LDH) were markedly elevated in a time-related manner. In a second group of baboons pretreated 10 min prior to ischaemia with ranolazine [(+/-)-N-(2,6-dimethyl-phenyl)-4[2-hydroxy-3-(2-methoxyphenoxy)propyl]-1 - piperazine acetamide dihydrochloride; RS-43285-193] at 500 micrograms kg-1 i.v., followed by continuous infusion of 50 micrograms kg-1 min-1, neither enzyme was significantly elevated at any time point. Similarly, serum levels of the cardiospecific isoenzyme CK2 were 8 fold greater in the controls than in the ranolazine-treated animals at 6 h. The results indicate that ranolazine pretreatment abolished cardiac enzyme release over a 5.5 h reperfusion period, indicating a potential protective effect.

A comparison of the effects of a series of anti-anginal agents in a novel canine model of transient myocardial ischaemia.

1. An anaesthetized canine model of transient myocardial ischemia (TMI) has been developed in which reproducible and reversible electrocardiographic (ECG) and haemodynamic responses are exacerbated by electrical pacing. 2. The model could separate the ECG and haemodynamic effects of compounds with anti-ischaemic properties. 3. Compounds known to possess peripheral or coronary vasodilator properties did not necessarily alleviate the ECG consequences of TMI since glyceryl trinitrate was active whereas dipyridamole was not. The effects of verapamil were complicated by its adverse conduction effects while lidoflazine inhibited the ECG changes only during the ischaemic phase and the 'metabolic modulator' oxfenicine worsened the ECG response. 4. In a model considered to lack coronary reserve, improvements observed in the ischaemic ECG and global ventricular function were considered to result from a direct myocardial effect of the drugs examined rather than by a vascular influence. This was provided to the greatest degree by the Ca2+-entry blockers nifedipine and nicardipine, with flunarizine adopting an intermediate position.

Comparative protective effects of nicardipine, flunarizine, lidoflazine and nimodipine against ischaemic injury in the hippocampus of the Mongolian gerbil.

1. Morphological changes characterizing delayed neuronal death (DND) of selectively vulnerable CA1 pyramidal cells in the hippocampus of the Mongolian gerbil brain occurred 72 h after transient (5 min) bilateral occlusion of the common carotid arteries. 2. Different groups of animals were treated 15 min before carotid artery occlusion and twice daily during the 72 h post-ischaemia period with either saline alone, nicardipine, flunarizine, lidoflazine or nimodipine at doses of 500 micrograms kg-1 intraperitoneally. 3. At 72 h the animals were killed and their brains examined histologically. Absolute cell counts were made from 5 sites distributed linearly throughout the hippocampal CA1 subfield in each hemisphere to determine the percentage DND in each group. Normal brains and those of sham-operated animals were included in the study for comparison. 4. Features of DND were distributed evenly throughout the CA1 subfield in both hemispheres in all groups of gerbils. Nicardipine, lidoflazine and flunarizine, but not nimodipine, were protective. This protection extended linearly throughout the hippocampus without altering the pattern of neuronal damage. 5. Compared to saline-treated (78.3 +/- 2.9% DND) and nimodipine-treated (76.5 +/- 3.4% DND) gerbils, the overall protection afforded by nicardipine (41.8 +/- 3.8% DND) was statistically significant. The effects of lidoflazine (53.6 +/- 7.1%) and flunarizine (55.8 +/- 3.9% DND) were of borderline significance. 6. Abnormal neurones appeared in normal and sham-operated brains to the extent of 4.5 +/- 1.0% and 4.6 +/- 0.4%, respectively. Such changes can be attributed to fixation artefacts. 7. The results demonstrate that overall protection is conferred on ischaemic hippocampal CA1 neurones by nicardipine and to a lesser extent by flunarizine and lidoflazine, but not by nimodipine.

The evaluation of the novel pressor activity of gamma-piperidinobutyramide (WY 20051, DF480).

1 gamma-Piperidinobutyramide (Wy 20051, DF480) injected intravenously evoked pressor responses in the anaesthetized ganglion blocked rat preparation over the dose range 2.4 x 10(-6)-3.0 x 10(-4) mol/kg. 2 High doses (greater than 3.8 x 10(-5) mol/kg) or even repeated submaximal doses (1.9 x 10(-5) mol/kg) of Wy 20051 caused tachyphylaxis of this pressor response. 3 The noradrenaline pressor-response curve was shifted significantly to the right of the control curve following a dose of Wy 20051 (1.5 x 10(-4) mol/kg cumulative). 4 The dose-response curve for the pressor action of Wy 20051 was potentiated in reserpine-treated anaesthetized rats. In contrast, tyramine-induced pressor responses were abolished. 5 Wy 20051 contracted the guinea-pig isolated aortic spiral preparation (3.8 x 10(-5)-6.0 x 10(-4) mol) and evoked constrictor responses in the perfused mesenteric vasculature preparation of the rat (5.9 x 10(-7)-1.2 x 10(-5) mol). At higher doses the responses were reduced. 6 Wy 20051-induced constrictor responses of the perfused mesentery were unaffected by blockade of alpha-adrenoceptors or by tachyphylaxis of 5-hydroxytryptamine receptors. 7 The time for abolition of Wy 20051-induced constrictor responses of the mesentery in a calcium-free medium was not significantly different from that required for noradrenaline, but was significantly greater than that for KCl (P less than 0.001). 8 Wy 20051 and noradrenaline, but not KCl, evoked constrictor responses in the depolarized rat mesenteric vasculature. 9 The results indicate that Wy 20051 evokes pressor responses which have some of the characteristics of those of noradrenaline. However, the responses are not elicited by an alpha-adrenoceptor mechanism.

The effect of lifarizine (RS-87476), a novel sodium and calcium channel modulator, on ischaemic dopamine depletion in the corpus striatum of the gerbil.

1. Unilateral ligation of the right common carotid artery in the anaesthetized gerbil for 3 h caused a 62.7% decrease in ipsilateral dopamine in the corpus striatum from 1.40 (+/- 0.13, n = 27) micrograms g-1 in the non-ischaemic hemisphere to 0.47 (+/- 0.07, n = 27) micrograms g-1 in the ischaemic hemisphere (all results are expressed as mean +/- s.e. mean). In sham-operated animals there were no differences in the dopamine levels (1.31 +/- 0.14 micrograms g-1, n = 11, left; 1.27 +/- 0.13 micrograms g-1, n = 11 in the right hemisphere). Animals with intact communicating arteries in the circulus arteriosus were excluded. 2. Lifarizine (RS-87476; 250, 500, but not 50, micrograms kg-1, i.p.) protected against this dopamine depletion showing only a 9.2% decrease at 250 micrograms kg-1, i.p. (P < 0.01) and no decrease at 500 micrograms kg-1, i.p. (P < 0.01). 3. Nicardipine (250 micrograms kg-1, p.o.) was effective when administered chronically once daily for 10 days (26.6% decrease, P < 0.05) but not when administered acutely at 50 micrograms kg-1, i.p.

Quantitative analysis on isolated organs of the autonomic blocking properties of indoramin hydrochloride (Wy 21901).

1. Indoramin is a competitive alpha-adrenoceptor blocking agent on the guinea-pig isolated vas deferens and aortic strip; the pA(2) value on the aorta is 7.4.2. Indoramin is devoid of beta-adrenoceptor blocking activity on the guinea-pig isolated trachea (10(-4)M) and the Langendorff preparation of the rabbit heart (10(-6)M). It also has no adrenergic neurone blocking action on the Finkleman preparation of the rabbit small intestine (10(-5)M).3. On the Langendorff preparation of the rabbit isolated heart, indoramin (above 10(-6)M) has cardio-inhibitory properties similar to those of propranolol.4. On the guinea-pig isolated ileum (10(-5)M) and trachea (10(-6)M), indoramin is devoid of anticholinergic activity, but has a potent antihistamine action which satisfies the criteria for competitive antagonism; the pA(2) value for this antagonism on the ileum is 8.2.5. Indoramin antagonizes 5-hydroxytryptamine on the rat isolated fundus and ileum; the pA(2) value for the antagonism on the ileum is 6.0.

Reduction by lifarizine of the neuronal damage induced by cerebral ischaemia in rodents.

1. The objective of this study was to evaluate the broad neurocytoprotective potential of the novel sodium-calcium ion channel modulator, lifarizine (RS-87476), in two rodent 72 h survival models of forebrain ischaemia. 2. Under fluothane anaesthesia, rats were subjected to 10 min four vessel occlusion and gerbils to either (i) 5 or (ii) 10 min bilateral carotid artery occlusion. 3. Rats were dosed parenterally solely post-ischaemia (reperfusion) in a series of five studies covering a range of intra-arterial/intraperitoneal (i.a./i.p.) combination doses from 2/10, 5/20, 20/100, 50/200 and 100/500 micrograms kg-1, where the initial loading dose was injected i.a. at 5 min. An i.p. dose was given at 15 min and repeated twice daily. In a sixth study, treatment at 50/200 micrograms kg-1 was deferred for 1 h. 4. Gerbils were treated (i) 15 min pre-ischaemia with either (a) 250, (b) 500 micrograms kg-1 i.p., or (c) 5 mg kg-1 by gavage (p.o.) for 3 days then at 1 h pre-ischaemia. Animals treated as (ii) received 500 micrograms kg-1 i.p. 15 min pre-ischaemia. The above doses were repeated twice daily for 3 days post-ischaemia for the respective groups. 5. In rats, the protective effect of lifarizine was regionally and cumulatively assessed in six brain regions (anterior and posterior neocortex, hippocampal CA1 subfield, thalamus, striatum, cerebellar Purkinje cells-brain stem) at each dose level. Cumulative (total) means +/-s.e.mean neurohistopathological scores(0-4) of 1.16+/-0.09 (n=5), 1.02+/-0.10 (n=5), 0.93+/-0.06 (n=6), 0.79+/-0.09 (n=9) and 0.45+/-0.16(n = 7), respectively, were obtained for the above treatment groups compared to the control (2.01 +/- 0.17,n = 16) group (P<0.0035). The score for the 1 h deferred treatment group was also significant at 0.77 +/- 0.10, n =5 (P< 0.0035). The normal group without ischaemia showed a score of 0.52 +/- 0.09 (n = 6).6. In gerbils, (i) percentage delayed neuronal death (DND) of hippocampal pyramidal cells in the CA1subfield was prevented at 250 (a) and 500 microg kg-' i.p. (b) (27.2+/- 14.6, n=6 and 26.9+/- 10.4%, n= 10 respectively, P<0.02) compared to controls (78.3+/-8.5%, n= 12) and by 5 mg kg-1 p.o. (c) (2.9+/-0.8%,n =l1, P <0.002). Mean +/- s.e.mean total brain scores (0-4) for each of 4 different features denoting cerebral 'oedema' were lower for normal brains (1.60 +/-0.34, n =6) and reduced in animals dosed at 250(a) (3.00+/-0.79, n=6) and 500 microg kg-1 i.p. (b) (3.75 0.36, n= 10) compared to controls (6.58+/-1.00,n = 12) (P< 0.02 -0.03). There was a linear relationship (r = 0.97) between the 'oedema' scores and percentage CA1 DND. Percentage CA1 DND in response to 10 min ischaemia (ii) was reduced(53.0+/-21.0%, n=6, P<0.05) compared to controls (100.0+/-0.0%, n=7).7 The significant neuroprotection shown by lifarizine in rodents substantiates findings in other species.These observations, together with its effect on ion channels and efficacy at extremely low doses offers novelty and suggests a broad spectrum of activity in ischaemia.

Neuroprotective efficacy of lifarizine (RS-87476) in a simplified rat survival model of 2 vessel occlusion.

1. A new, modified rat two vessel occlusion model (with hypotension) was established and the neuroprotective efficacy of the novel agent lifarizine (RS-87476) was examined. 2. The two vessel occlusion model used in the study was a modification of the model described in the literature, whereby we have obviated the need to use a muscle relaxant and intubate the trachea to provide ventilatory support by providing a tight fitting face mask attached to the ventilator. Furthermore, the need to combine exsanguination and additional pharmacological means of inducing the mandatory hypotension (50 mmHg), required to decrease brain blood perfusion pressure, has been removed by simply manipulating the concentration of the already present halothane anaesthetic. 3. The appropriate level of hypotension having been reached, microvascular clips were applied to bilaterally occlude the common carotid arteries for 12 min. This resulted in a loss of the cortical EEG activity. Local cerebral blood flow was measured 6 min into the occlusion period, using the fully quantitative [14C]-iodoantipyrine autoradiographic technique, in a separate group of rats (n = 5). This illustrated the lack of any blood flow, in the areas under study, during the period when there was an isoelectric cortical EEG pattern. 4. The high grade global ischaemic lesion which occurred gave quantifiable neuronal damage in several vulnerable regions of the brain, namely, the hippocampal CA1 sub-field, cortex, thalamus, striatum, and cerebellar brain stem (Purkinje cells). 5. Following the global ischaemic insult the rats were allowed to recover for 72 h before assessment of the damage, during which time one group of rats (n = 11) received 100 micrograms kg-1 lifarizine i.a. 5 min post-occlusion, 500 micrograms kg-1 lifarizine i.p. 15 min post-occlusion, and 500 micrograms kg-1 lifarizine i.p. twice daily for 72 h. A second group of rats (n = 12) was treated with appropriate volumes of vehicle (0.4 ml kg-1 i.a. and 2 ml kg-1 i.p.) at identical time points. 6. Histopathological damage was assessed, from cresyl violet and haematoxyline/eosin stained sections, using a scoring system of 0-6 (no damage-complete neuronal death). The dosing regimen of lifarizine gave reduced damage in the hippocampal CA1 sub-field (4.1 +/- 0.3 to 2.8 +/- 0.6) and striatum (1.7 +/- 0.3 to 1.2 +/- 0.3) and significant neuroprotection in the anterior cortex (2.0 +/- 0.2 to 1.2 +/- 0.2; p < 0.05), thalamus (1.5 +/- 0.2 to 0.8 +/- 0.2; p < 0.01), posterior cortex (1.5 +/- 0.2 to 1.0 +/- 0.2; p < 0.05) and cerebellar brain stem (0.9 +/- 0.2 to 0.4 +/- 0.1; p < 0.01). The overall mean brain score was significantly reduced (from 1.5 +/- 0.1 to 0.9 +/- 0.2). 7. These data show that the newly modified 2 vessel occlusion model produced a quantifiable level of ischaemic damage and that the novel agent lifarizine is neuroprotective in the model.

Activators and inactivators of calcium channels: effects in the central nervous system.

The interactions of calcium antagonists or channel activators with the different classes of calcium channel are reviewed with particular emphasis on interactions with neuronal tissue; reasons for the failure of calcium antagonists to inhibit neurotransmitter release under normal circumstances are outlined. Calcium antagonists may be protective in several pathological situations and the possibilities of protection against ischaemic damage in the central nervous system are evaluated.