Discovery of 4-[3-(trans-3-dimethylaminocyclobutyl)-1H-indol-5-ylmethyl]-(4S)-oxazolidin-2-one (4991W93), a 5HT(1B/1D) receptor partial agonist and a potent inhibitor of electrically induced plasma extravasation.

Utilizing a pharmacophoric model of binding of 3-(2-aminoethyl)indoles to 5HT(1B/1D) receptors, we identified the 3-aminocyclobutyl group as a potential ethylamine isostere. A novel multidimensional chemometric approach was used to predict the intrinsic activity (degree of agonism) at the receptor. A qualitative model for pharmacokinetic properties was then used to guide the synthesis toward molecules likely to have oral bioavailability in humans. A novel synthetic route to 3-(3-dimethylaminocyclobutyl)indoles was developed. Analogues showed generally lower intrinsic activity at 5HT(1B/1D) receptors than their ethylamine counterparts. 4-[3-(trans-3-Dimethylaminocyclobutyl)-1H-indol-5-ylmethyl]-(4S)-oxazolidin-2-one (4991W93, 1) was identified as a partial agonist against 5HT(1B/1D) receptors, with low intrinsic activity. This molecule also has significant activity against 5HT(1F) receptors but is selective over other 5HT receptors. In addition this compound was found to be an exceptionally potent inhibitor of electrically induced plasma extravasation. Compound 1 may have utility in the treatment and prophylaxis of migraine.

The pharmacological properties of the novel selective 5-HT3 receptor antagonist, alosetron, and its effects on normal and perturbed small intestinal transit in the fasted rat.

The purpose of this study was to investigate the pharmacological properties of the novel, selective 5-HT3 receptor antagonist, alosetron, and its effects on transit time in both the normal and perturbed small intestine of the rat. Alosetron concentration-dependently inhibited radioligand binding in membranes containing rat and human 5-HT3 receptors with estimated pKi values of 9.8 (n = 3) and 9.4 (n = 6), respectively. In selectivity studies alosetron had little or no significant affinity for any of the many other receptors and ion channels studied. Alosetron potently antagonized the depolarization produced by 5-HT in the rat vagus nerve (estimated pKB value of 9.8, n = 25). In anaesthetized rats, i. v. administration of alosetron inhibited 2-methyl-5-HT induced bradycardia (Bezold Jarisch index) at 1 and 3 microg kg-1, with an agonist dose ratio of approximately 3.0 at 1.0 microg kg-1, = 3-5). Alosetron administered via the duodenum also inhibited this reflex, with duration of action that was significantly longer than that seen with ondansetron (120-60 min, respectively, n = 6). Alosetron had no significant effect on normal small intestinal propulsion in the rat, but fully reversed the increase in intestinal propulsion (96%, n = 3) produced by egg albumin challenge. Alosetron is a highly selective 5-HT3 antagonist which normalizes perturbed small intestinal propulsion. Previous clinical data in IBS patients together with the transit data provide a good rationale for further studies with alosetron in IBS patients.

Cranial vascular effects of zolmitriptan, a centrally active 5-HT1B/1D receptor partial agonist for the acute treatment of migraine.

The anti-migraine drug zolmitriptan is a novel 5-HT1B/1D receptor partial agonist which, unlike sumatriptan, has been shown to cross the intact blood-brain barrier. In this study we examined whether or not the ability to access the cerebro-vascular intima affects the way in which a centrally-active 5-HT1B/1D receptor agonist influences cranial haemodynamics. The effects of zolmitriptan on carotid arterial blood flow distribution were studied in anaesthetised cats using radiolabelled microspheres. Zolmitriptan (10-1000 microg kg(-1) i.v.) selectively reduced arteriovenous-anastomotic (AVA) conductance producing a maximum decrease of 92.5+/-2.3%. The drug also produced a modest reduction in extra-cerebral conductance (23.9+/-6.5% maximum reduction at 30 microg kg(-1), i.v.), but was without effect on cerebral conductance. Using laser doppler flowmetry in anaesthetised cats, zolmitriptan (1-30 microg kg(-1), i.v.) produced dose-dependent decreases in ear microvascular conductance (15+/-5 to 60+/-6%) which mirrored decreases in carotid arterial conductance (12+/-11 to 61+/-5%). By contrast, zolmitriptan at doses up to 1000 microg kg(-1) was without effect on cerebral microvascular conductance. Although zolmitriptan crosses the blood-brain barrier and can therefore access the cerebro-vascular intima, this study suggests that this property does not adversely affect cerebrovascular function.

Nitric oxide and the haemodynamic profile of endotoxin shock in the conscious mouse.

1. The release of cytokines following administration of endotoxin and the contribution of nitric oxide (NO) to the subsequent haemodynamic profile were investigated in the conscious mouse. 2. Administration of endotoxin (E. Coli, 026:B6, 12.5 mg kg(-1), i.v.) elevated the concentration of tumour necrosis factor-alpha (TNF-alpha) in the plasma within 0.5 h, reaching a maximum at 2 h and returning to control concentrations by 4 h. In addition, the concentration of interleukin-6 (IL-6) in the plasma was also elevated within 1 h, reaching a maximum at 3 h and remaining elevated throughout the 12 h of study. 3. Endotoxin (12.5 mg kg(-1), i.v.) induced the expression of a Ca2+-independent (inducible) NO synthase in the mouse heart and elevated the concentrations of nitrite and nitrate in the plasma within 4 h, reaching a maximum at 12 h. This was accompanied by a progressive fall in blood pressure over the same period. 4. The vasopressor effect of noradrenaline (0.5-4 microg kg(-1) min(-1), i.v.) administered as a continuous infusion was significantly attenuated 7 h after endotoxin (12.5 mg kg(-1), i.v). 5. The NO synthase inhibitor NG-monomethyl-L-arginine HCl (L-NMMA; 1-10 mg kg(-1), i.v. bolus) reversed the fall in blood pressure when administered 7 h after endotoxin (12.5 mg kg(-1), i.v.). 6. In an attempt to maintain a constant blood concentration, L-NMMA was administered as a continuous infusion (10 mg kg(-1) h(-1), i.v.), beginning 4 h after a lower dose of endotoxin (6 mg kg(-1), i.v.). Such treatment prevented the fall in blood pressure and the elevation of nitrite and nitrate in the plasma throughout the 18 h of observation. 7. The fall in blood pressure following endotoxin (3 mg kg(-1), i.v.) was significantly reduced throughout the 18 h of observation in homozygous mutant mice lacking the inducible NO synthase. 8. In summary, we have developed a model of endotoxin shock in the conscious mouse in which an overproduction of NO by the inducible NO synthase is associated with the haemodynamic disturbances. This model, which exhibits many of the characteristics of septic shock in man, will enable the study of the pathology of this condition in more detail and aid the investigation of potential therapeutic agents both as prophylactics and, more importantly, as treatments.

Canine renovascular responses to sumatriptan and 5-carboxamidotryptamine: modulation through endothelial 5-HT1-like receptors by endogenous nitric oxide.

1. In anaesthetized dogs, intra-left atrial (i.l.a.) administration of the 5-HT1-like receptor agonists, sumatriptan (1-10 micrograms kg-1) and 5-carboxamidotryptamine (0.03-0.3 micrograms kg-1) produced dose-related reductions in renal blood flow and vascular conductance, which were characterized by their rapid onset and recovery. 2. In these animals, i.v. administration of the inhibitor of nitric oxide (NO) synthase, NG-nitro-L-arginine methyl ester (L-NAME; 10 mg kg-1) significantly augmented the renal vasoconstrictor responses to i.l.a. sumatriptan and 5-carboxamidotryptamine. 3. The effects of L-NAME upon these responses to sumatriptan and 5-carboxamidotryptamine were significantly reversed by subsequent i.v. administration of L-arginine (1000 mg kg-1). 4. L-NAME significantly attenuated the systemic hypotensive responses to i.v. acetylcholine (0.3-3 micrograms kg-1) and this effect was also reversed by L-arginine. 5. L-NAME had no effect upon the renal vasoconstrictor response to i.l.a. administration of angiotensin II, nor did it affect the renal vascular conductance recovery response to brief mechanical occlusion of the renal artery. 6. These data suggest that sumatriptan and 5-carboxamidotryptamine stimulate the release of NO through the activation of a 5-HT1-like receptor located on the endothelial cells. 7. It is concluded that in canine renal vasculature, 5-HT1-like agonists (and presumably endogenous 5-hydroxytryptamine) can cause simultaneous activation of a 5-HT1-like receptor on both vascular smooth muscle and endothelial cells. The net renal vascular response to these agonists is therefore a function of both the vascular smooth muscle vasoconstriction and the concurrent vasodilator influence of NO released from the endothelium.

Vascular 5-HT1-like receptors mediating vasoconstriction and vasodilatation: their characterization and distribution in the intact canine cardiovascular system.

1. In anaesthetized dogs, intra-left atrial administration of 5-hydroxytryptamine (5-HT) and selected tryptamine analogues (5-carboxamidotryptamine, 5-CT; 5-methyl tryptamine, 5-MT; alpha-methyl 5-hydroxytryptamine, alpha-HT; sumatriptan, Sum) in the presence of ketanserin and MDL72222 (5-HT2 and 5-HT3 receptor antagonists, respectively), produced dose-related changes in carotid, coronary and renal vascular conductance mediated by vascular 5-HT1-like receptors. 2. In the carotid vascular bed, 5-HT, 5-MT, alpha-HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5-HT = Sum > 5-MT > alpha-HT. By contrast in this vascular bed, 5-CT was a potent vasodilator. 3. In the coronary vascular bed, 5-HT, 5-CT, 5-MT and alpha-HT were vasodilators with a rank order of potency (comparing ED50 values) of 5-CT > 5-HT > 5-MT > alpha-HT. In this vascular bed, Sum was without effect. 4. In the renal vascular bed, 5-HT, 5-CT, 5-MT, alpha-HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5-CT > 5-HT > Sum > 5-MT > alpha-HT. 5. The coronary (and carotid) vasodilator responses to 5-CT were antagonized by the 5-HT1-like receptor antagonists, spiperone (1 mg kg-1) and methiothepin (0.1 mg kg-1), whereas the renal vasoconstrictor responses to this tryptamine analogue were antagonized only by methiothepin. 6. It is concluded from these studies that agonist finger-printing in vivo, using tryptamine analogues,identifies and confirms the functional presence of at least two pharmacologically distinct subtypes of the 5-HT1-like receptor in the intact canine cardiovascular system. These two subtypes are located on the vascular smooth muscle and mediate direct vasoconstriction and vasodilatation responses in vivo.7. In addition, these studies confirm that the distribution of these subtypes within the major vascular beds, shows a marked heterogeneity. The carotid vascular responses to the tryptamine analogue sindicate the presence of both the vasodilator and the vasoconstrictor subtypes. The coronary vascular responses to these analogues are, however, consistent with presence of the vasodilator subtype, only. By contrast, the renal vascular responses to these analogues indicates only the presence of the vasoconstrictor subtype.

Digoxin and digoxin derivative induced arrhythmias: in vitro binding and in vivo abolition of arrhythmias by digoxin immune Fab (DIGIBAND).

OBJECTIVE: The aim was to compare the binding characteristics of a highly purified digoxin specific antigen binding fragment (digoxin immune Fab: DIGIBIND) with digoxin and with two commonly used derivatives of digoxin, beta methyl digoxin and beta acetyl digoxin, and to assess its ability to abolish the arrhythmogenic effects of these digitalis glycosides. METHODS: The binding characteristics of DIGIBIND with digoxin, beta methyl digoxin, and beta acetyl digoxin were assessed in vitro by measuring their ability to inhibit the binding of DIGIBIND to 3H-digoxin. From these studies the affinities of the interactions between DIGIBIND and these glycosides, and the binding capacity of DIGIBIND for each of these glycosides, could be measured. The ability of DIGIBIND to abolish the arrhythmogenic effects of digoxin, beta methyl digoxin, and beta acetyl digoxin was assessed using an in vivo anaesthetised guinea pig model (n = 36, weight 300-400 g), in which these glycosides were infused intravenously (50 micrograms.kg-1 x min-1) until the onset of ventricular arrhythmias, at which point the total amount of glycoside given was calculated. A single bolus dose of either vehicle or DIGIBIND was then given intravenously, and the time to restoration of normal cardiac rhythm noted. After the administration of DIGIBIND, a second infusion of the same glycoside was given to reinitiate the ventricular arrhythmias. The time to onset of the arrhythmias was noted, and the additional amount of glycoside given calculated. RESULTS: In vitro studies showed the binding of DIGIBIND to 3H-digoxin to be inhibited by digoxin and by the two derivatives. The affinities of these interactions with DIGIBIND were significantly different, that for digoxin being some twofold greater than that for beta methyl digoxin and beta acetyl digoxin. The ED50 concentrations were 14.1 (95% CI 12.2, 15.2), 29.2(26.1, 32.7), and 36.2(33.0, 39.8) nM, respectively. However, there were no significant differences between these glycosides in their binding capacities. The in vivo studies showed that intravenous infusion of digoxin, beta methyl digoxin, or beta acetyl digoxin induced similar ventricular arrhythmias. The onset of the arrhythmias was clearly discernible, and required a significantly lower dose of digoxin compared with that of beta methyl digoxin and beta acetyl digoxin. These doses were 667(SEM 55), 868(33), and 854(40) nmol.kg-1, respectively. Termination of the infusion had no effect on the arrhythmias, and in those animals which received a bolus intravenous injection of saline there was no return to normal cardiac rhythm. By contrast, in animals which received a bolus intravenous injection of DIGIBIND, there was complete abolition of the arrhythmias within 4-6 min. Although the dose of DIGIBIND given to abolish digoxin induced arrhythmias was approximately 25% less than that given to abolish beta methyl digoxin and beta acetyl digoxin induced arrhythmias (p < 0.05), the time to restoration of normal cardiac rhythm after DIGIBIND was not significantly different for digoxin compared with beta methyl digoxin and beta acetyl digoxin, at 4.6(0.9), 4.9(0.8), and 5.7(0.8) min, respectively. To reinitiate the arrhythmias in those animals which had received DIGIBIND, a dose of glycoside was required which was not significantly different from that given prior to the DIGIBIND. This observation therefore confirmed the stoichiometric relationship between DIGIBIND and each of the glycosides in respect of the neutralising action of DIGIBIND in abolishing the arrhythmogenic effects of these agents. CONCLUSIONS: Although there is some small difference in the affinities of the binding interactions, there is no difference in the binding capacities of DIGIBIND for digoxin, beta methyl digoxin, or beta acetyl digoxin in vitro. These binding interactions are manifest as the ability of DIGIBIND to abolish the arrhythmogenic effects of digoxin and the two derivatives in vivo.

The effects of combined angiotensin converting enzyme inhibition and beta-adrenoceptor blockade on plasma renin activity in anaesthetized dogs.

1. The effects of beta-adrenoceptor blockade on the changes in plasma renin activity (PRA) following angiotensin enzyme (ACE) inhibition were investigated in pentobarbitone-chloralose anaesthetized dogs. 2. ACE-inhibition, with enalapril (2 mg kg-1), caused a significant reduction in systemic arterial blood pressure (BP) with little or no effect on cardiac function, and a significant elevation of plasma renin activity (PRA). By contrast beta-adrenoceptor blockade with atenolol (1 mg kg-1), caused a similar reduction in BP but in addition, significantly reduced cardiac function and PRA. 3. A combination of enalapril with atenolol, caused a significant reduction in BP, cardiac function and PRA, hence there was no elevation of PRA, as was seen following ACE-inhibition with enalapril alone. 4. The observations with beta-adrenoceptor blockade alone, show that there is an important homeostatic role for the renal sympathetic innervation, mediated by beta-adrenoceptors, in controlling basal renin levels. Furthermore, the renal sympathetic innervation appears to be an important contributor to the renin release caused by an ACE-inhibitor as the additional presence of a beta-adrenoceptor blocking agent will prevent this release. 5. BW B385C (2 mg kg-1), which combines both ACE-inhibition and beta-adrenoceptor blocking properties, also produced reductions in BP and cardiac function similar to those seen with the enalapril/atenolol combination. In addition, for an equivalent degree of ACE-inhibition by BW 385C, to that seen with enalapril alone, the elevation of PRA was attenuated. 6. A combination of ACE-inhibition and beta-adrenoceptor blocking activity in a single entity, such as BW B385C, therefore also produces a reduced renin release when compared with an ACE-inhibitor, such as enalapril. This provides further confirmation of the importance of the renal sympathetic innervation in the renin response to ACE-inhibition, and supports the concept of combining ACEinhibition with beta-adrenoceptor blockade.

Inotropic polyazapentalene sulmazole analogues.

Aryl substituted 1H-imidazo[1,2-a]imidazole 8, imidazo[2,1-b]thiazole 9, 1,4-dihydroimidazo[4,5-d]imidazole 11, and 1(2),4-dihydroimidazo[4,5-c]pyrazoles 12-17 have been prepared. An X-ray crystallographic study confirmed the structure of 8 and showed this analogue to exist as the 1H-tautomer. These heterocycles were evaluated as inotropic agents and analogues 12, 15, and 17 found to display inotropic properties which were less potent in vitro, but more potent in vivo, than those of sulmazole. Structure-activity relationships are discussed.

Inotropic activities of imidazopyridines.

A series of 2-substituted 1H-imidazo[4,5-b]pyridines and the isomeric 1H-imidazo[4,5-c]pyridine derivatives has been prepared and evaluated as inotropic agents. The 1H-imidazo-[4,5-b] derivatives were found to be consistently more potent than their isomers in the [4,5-c] series in isolated guinea pig papillary muscle preparations. Structure-activity relationships and the species-dependence of inotropic potencies are discussed.

Cardiotonic 'C' ring modified isomazole analogues.

Isomazole analogues which have achiral electron withdrawing substituents at the 4'-position and analogues with heterocyclic 'C' rings have been synthesized and evaluated as inotropic agents. It was found that pyridyl could replace phenyl in the 'C' ring without loss of activity. The 4'-methylsulphonyl, -cyano, -carboxamido, and acetyl analogues had similar inotropic potencies to Isomazole whilst displaying superior cardiovascular profiles in in vivo studies.

Inotropic "A" ring substituted sulmazole and isomazole analogues.

A series of "A" ring substituted sulmazole and isomazole analogues have been prepared and evaluated as inotropic agents. pKA's, protonation sites, and log P values were measured for selected compounds and their electronic properties were calculated. No simple correlation between inotropic activity and pKA, protonation site, or log P value was observed. However, in vitro inotropism did correlate with the calculated charge density of the "B" ring imidazo nitrogen atom. The 6-position of sulmazole appeared to be the most tolerant toward substituents, the 6-amino derivative 7 being a more potent inotrope than sulmazole itself. 4-Methoxyisomazole 13 had comparable in vivo inotropic properties to those of isomazole.

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.

Cardiac and renovascular effects in the anaesthetized dog of BW A575C: a novel angiotensin converting enzyme inhibitor with beta-adrenoceptor blocking properties.

1. In the anaesthetized open-chest dog, BW A575C (N-(1-(S)-carboxy-5-[4(3- isopropylamino-2-(R,S)-hydroxypropoxy)indole-2- carboxamido]pentyl)-(R,S)-alanyl-(S)-proline) causes a dose-dependent inhibition of the isoprenaline response (increased cardiac rate). In this preparation BW A575C is approximately 50 times less active than propranolol, and 500 times less active than pindolol at the cardiac beta 1-adrenoceptor. 2. At equieffective cardiac beta 1-adrenoceptor blocking doses in the anaesthetized, open-chest dog, BW A575C (5.0 mg kg-1, i.v.) significantly reduces diastolic blood pressure and reduces cardiac contractility and rate. By contrast, propranolol (0.1 mg kg-1, i.v.) and pindolol (0.01 mg kg-1, i.v.) have little effect on diastolic blood pressure, but significantly reduce cardiac contractility and rate. The effects of BW A575C on cardiac rate are not significantly different from those of propranolol and pindolol, but its effects on cardiac contractility are significantly less than those of propranolol. BW A575C also produces some increase in left ventricular internal dimensions at end-diastole. This small cardiac dilatation is not significantly different from that observed with pindolol but is significantly less than that of propranolol. 3. In the anaesthetized closed-chest dog, BW A575C causes a dose-dependent inhibition of the angiotensin I pressor response. In this preparation BW A575C is approximately equiactive with enalapril at preventing the pressor response due to conversion of exogenous angiotensin I to angiotensin II (inhibition of angiotensin converting enzyme (ACE)). 4. At equieffective ACE-inhibition doses in the anaesthetized, closed-chest dog, BW A575C (1.0 mg kg-1 by i.v. infusion) significantly reduces diastolic blood pressure, cardiac contractility and rate, whereas enalapril (1.0 mg kg-1 by i.v. infusion) only significantly reduces diastolic blood pressure. This blood pressure lowering effect of enalapril is not significantly different from that of BW A575C. In this preparation BW A575C and enalapril also significantly increase renal blood flow, and renal excretion of urine and Na+. There is however no significant difference between their renovascular effects. 5. These studies demonstrate that BW A575C produces changes in cardiac and renovascular function which can be ascribed to its being an ACE-inhibitor and a beta-adrenoceptor blocking agent. The combination of these pharmacological properties results in a fall in blood pressure without compromising either cardiac performance or renal function.

Comparative analysis of two types of 5-hydroxytryptamine receptor mediating vasorelaxation: differential classification using tryptamines.

Two receptors mediating relaxant responses to 5-hydroxytryptamine (5-HT) were studied comparatively in rings of rabbit jugular vein contracted with U-46619 (10 nmol/l). At low concentrations of 5-HT (0.001-0.1 mumol/l) vascular relaxation was mediated indirectly by the endothelial 5-HT receptor previously described by Leff et al. (1987). In preparations denuded of endothelium, higher concentrations of the amine (0.03-30 mumol/l) caused relaxation responses directly, presumably via a receptor located on the smooth muscle cells. Similarity between the receptors was evident in that both were susceptible to antagonism by methysergide, but resistant to blockade by ketanserin and MDL 72222. In these respects, the receptors qualified for a '5-HT1-like' classification. Consistent with this, 5-carboxamidotryptamine demonstrated a higher agonist potency than 5-HT at the receptor mediating relaxation directly. However, in endothelium-intact jugular vein rings this potency order was reversed, showing that the endothelial 5-HT receptor did not satisfy completely the criteria for a '5-HT1-like' designation. When the activities of a single set of tryptamines were compared in endothelium-intact and -denuded jugular vein rings, different affinity and relative efficacy estimates were obtained, confirming that two distinct 5-HT receptors mediate relaxation responses in this tissue. The most striking difference between these two receptor types was demonstrated by alpha-methyl-5-HT since it expressed a high affinity comparable to 5-HT at the endothelial receptor, but was inactive at the receptor in endothelium-denuded preparations at concentrations up to 30 mumol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

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 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.

The protective action of allopurinol in an experimental model of haemorrhagic shock and reperfusion.

Haemorrhagic shock was induced in anaesthetized, open-chest dogs by controlled arterial bleeding, sufficient to reduce and maintain mean arterial blood pressure at 40 mmHg for 30 min. The blood volume was then restored to the pre-shock level by rapid, intravenous reinfusion of the blood shed during the shock period. Haemorrhagic shock produced significant haemodynamic changes, characterized by a marked depression of myocardial function. Cardiac output (1226 +/- 57 ml min-1), peak aortic blood flow (6030 +/- 383 ml min-1) and maximum rate of rise of left ventricular pressure (2708 +/- 264 mmHg s-1) were all reduced by more than 50%. The haemodynamic profile was markedly improved by reinfusion of shed blood but this improvement was not sustained. There was a gradual decline such that 50% of the untreated animals suffered complete circulatory collapse and death between 60 and 120 min following reinfusion. Neither haemorrhagic shock, nor reinfusion of shed blood produced any consistent or significant changes in the myocardial adenine nucleotide pool. The ATP, ADP and AMP levels were, respectively, 25.9 +/- 4.2; 15.6 +/- 1.0; 4.3 +/- 1.9 nmol g-1 protein, before haemorrhagic shock; 21.6 +/- 3.4; 21.5 +/- 2.5; 10.2 +/- 2.7 nmol g-1 protein, after 30 min haemorrhagic shock; and 29.9 +/- 3.9; 16.5 +/- 1.2; 4.2 +/- 1.1 nmol g-1 protein, 60 min following reinfusion of shed blood. Pretreatment with allopurinol (50.0 mg kg-1 i.v.), 60 min before inducing haemorrhagic shock, had no significant effect upon the haemodynamic response to shock, but did prevent the gradual decline seen following reinfusion in the untreated animals. All of the allopurinol-treated animals displayed significantly better haemodynamic profiles than the untreated animals, furthermore, there was a 100% survival rate in this group. 5 Allopurinol had no significant effect upon the myocardial adenine nucleotide pool either during haemorrhagic shock or following reinfusion of shed blood.

Evaluation of the QA interval as an index of cardiac contractility in anaesthetised dogs: responses to changes in cardiac loading and heart rate.

The response of a simple systolic time interval, the interval between the Q wave and the onset of the aortic blood pressure pulse (the QA interval), to changes in cardiac contractility, cardiac loading, and heart rate was evaluated in anaesthetised open chest dogs. The QA interval was found to be sensitive to increases in cardiac contractility, being reduced (maximum reduction 33.7(1.5) ms) in a dose related manner by infusions of isoprenaline, but was unaffected by reductions in cardiac loading (maximum reduction in diastolic blood pressure 39.7(5.9) mmHg), induced by infusion of sodium nitroprusside, or changes in heart rate (125 to 275 beats X min-1), induced by cardiac pacing. This contrasted with the response of a simultaneous alternative measurement of cardiac contractility, the maximum rate of rise of left ventricular pressure (LVdP/dtmax). Like the QA interval, LVdP/dtmax was also found to be sensitive to increased cardiac contractility (maximum increase 3583(401) mmHg X s-1) and was unaffected by changes in heart rate. Unlike the QA interval, however, LVdP/dtmax was consistently reduced (maximum reduction 1146(200) mmHg X s-1), in a dose related manner, by reductions in cardiac loading. The simplicity of the QA interval and its apparently selective response to changes in cardiac contractility suggests that this index could find a wider application in experimental and clinical settings.

Comparative pharmacology and clinical efficacy of newer agents in treatment of heart failure.

The animal and human pharmacology of several new drugs (prazosin, trimazosin, pirbuterol, and carbazeran) useful in the treatment of congestive heart failure (CHF) is delineated in relation to the pharmacology of other agents employed for CHF management. Prazosin and trimazosin are selective alpha 1-blockers that cause a balanced increase in cardiac output (CO) and reduction in left ventricular filling pressure (LVFP); the reduction in diastolic blood pressure with these drugs is significantly related to increase in treadmill exercise, fall in LVFP, and increase in CO. Pirbuterol is a relatively selective beta 2-agonist with somewhat greater effects on CO than on LVFP. Early promise in CHF therapy is being shown by a novel series of cyclic adenosine monophosphate (cAMP) phosphodiesterase inhibitors with combined direct inotropic and vasodilator effects. Double-blind long-term studies demonstrate persistent efficacy of prazosin and trimazosin in CHF as measured by improvement in New York Heart Association functional class, treadmill exercise performance, and noninvasive measures of cardiac function; these data are supported by studies in which repeat cardiac catheterization has been performed after several months of therapy. Double-blind studies of other CHF drugs are in progress.