Synthesis of halogenated trimetoquinol derivatives and evaluation of their .beta.-agonist and thromboxane A2 (TXA2) antagonist activities

The 5,8-difluoro (4), 5-iodo (5), 8-iodo (6), and 5-trifluoromethyl (7) derivatives of trimetoquinol (TMQ, 1) have been synthesized and evaluated for their ability to stimulate beta 1 (guinea pig atria) and beta 2 (guinea pig trachea) adrenoceptors as well as for their inhibitory activity against U46619 [a thromboxane A2 (TXA2) mimetic]-mediated contraction of rat thoracic aorta and human platelet aggregation. Both 5 and 6 were considerably less active than TMQ on both beta-adrenergic systems and gave a rank order of stimulatory potency of 1 much greater than 6 greater than or equal to 5. Similarly, iodine substitution at either position also caused a reduction in TXA2 antagonist activity with a rank order potency of 1 greater than 6 much greater than 5. Compared to 1, however, 5-iodo-TMQ (5) showed a marked selectivity for blockade of U46619 responses in rat aorta over human platelets. On beta-systems, 4 had reduced potency compared to TMQ and was similarly nonselective. Introduction of a trifluoromethyl group at the 5-position of TMQ completely abolished both beta 1- and beta 2-adrenergic agonist activities while imparting weak antagonist activity on beta 1 receptors. On TXA2 systems, both 4 and 7 possessed significantly decreased inhibitory activity compared to TMQ. The synthetic approaches to the synthesis of 8-(trifluoromethyl)-TMQ (8) are also described. The enantiomers of the 8-fluoro derivative (3) of TMQ were separated on a preparative Chiralcel OD column and evaluated on beta-adrenergic systems and TXA2 systems. On beta-adrenergic systems, (S)-(+)-8-fluoro-TMQ was at least 10-fold more potent than (R)-(-)-8-fluoro-TMQ. Conversely, (R)-(-)-8-fluoro-TMQ was approximately 14-fold more potent as an antagonist of TXA2-mediated aggregation in human platelets than (S)-(+)-8-fluoro-TMQ. In contrast to platelets, (S)-(+)-8-fluoro-TMQ was an agonist in rat aorta whereas (R)-(-)-8-fluoro-TMQ was an antagonist.

Biochemical activities of trimetoquinol analogs at human beta(1)- and beta(3)-adrenergic receptors

The biochemical activities of trimetoquinol (TMQ) analogs were evaluated at the human beta(1)- and beta(3)-adrenergic receptor (AR) subtypes expressed in Chinese hamster ovary cells. In radioligand binding assays, the 1-benzyl iodine-substituted analogs exhibited higher binding affinities at both beta(1)- and beta(3)-AR subtype as compared to TMQ. In cAMP accumulation assays, these analogs exhibited high potencies at both beta(1)- and beta(3)-AR. The 3',5'-diiodo-4'-amino analog of TMQ was the most potent beta(3)-AR agonist, 17-fold more potent at the beta(3)-AR versus the beta(1)-AR. Masking of the 6,7-dihydroxy group of the catechol ring of 3',5'-diiodo-4'-acetamido analog of TMQ, a potent beta(1)- and beta(3)-AR agonist, abolished activity at both beta-AR subtypes. Furthermore, substitution of a strong electron withdrawing group such as the trifluoromethyl moiety at the 1-benzyl ring of TMQ dramatically decreased potency at beta(1)- and beta(3)-AR compared to TMQ. Replacement of the 1-benzyl ring of TMQ with a naphthalene ring did not alter affinity but reduced potency of resulting 1-naphthylmethyl and 2-naphthylmethyl analogs at beta(1)- and beta(3)-AR compared to TMQ. Our results define the structural and electronic properties of substituents on TMQ necessary for potent activation of beta(1)- and beta(3)-AR and suggest that further modifications of the 1-benzyl iodine-substituted analogs may yield potent beta(3)-AR agonists.

Biochemical and functional characterization of 1-benzyl substituted trimetoquinol affinity analogs on rat and human beta-adrenoceptors

The site of interaction for the 1-(3',4',5'-trimethoxybenzyl) group of trimetoquinol (TMQ) with beta-adrenoceptors (beta-ARs) is important for the rational design of highly potent and beta3-AR-selective analogs. 1-Benzyl ring-substituted TMQ analogs were evaluated for binding affinities and biochemical activities (cyclic AMP accumulations) in Chinese hamster ovary (CHO) cells expressing the rat and human beta3-AR, and for functional activities on isolated rat tissues. Binding affinities (K1 approximately 0.055 to 1.5 microM) for the rat beta3-AR and potencies for adenylyl cyclase activation (K(act) approximately 0.43 to 2;5 nM) of the 3'-monoiodo or 3',5'-diiodo derivatives with 4'-isothiocyanato-, 4'-amino, 4'-acetamido, or 4'-alpha-haloacetamido substitutions were higher than those of (-)-isoproterenol, and comparable to those of BRL 37344 [(+/-)-(R*,R*-[4-[2-[[2-(3-chlorophenyl)-2-hydroxy-ethyl]amino]propyl]ph enoxy]-acetic acid sodium]. A similar rank order of binding affinities (K(i) approximately 0.11 to 2.5 microM) and potencies (K(act) approximately 0.45 to 9.5 nM) was obtained for TMQ analogs on the human beta3-AR. The 4'-acetamido and 4'-alpha-chloroacetamido analogs of 3',5'-diiodoTMQ were more potent than (-)-isoproterenol in rat atria (beta1-AR) and rat trachea (beta2-AR) and exhibited partial agonist activities, whereas full agonist activities were observed in rat esophageal smooth muscle (EC50 approximately 2-8 nM, beta3-AR). 4'-alpha-Chloroacetamido-3',5'-diiodoTMQ-mediated chronotropic responses in atria were sustained and resistant to washout. Further, the 4'-alpha-chloroacetamido and 4'-alpha-bromoacetamido analogs of 3',5'-diiodoTMQ demonstrated significant concentration-dependent irreversible binding to the rat beta3-AR. Reversible beta-AR agonists such as (-)-isoproterenol, BRL 37344, and 4'-acetamido-3',5'-diiodoTMQ or nucleophilic 1-amino acids (lysine, glutathione, cysteine) did not protect against this irreversible binding. Thus, the lipophilic 1-benzyl ring of TMQ analogs interacts with a hydrophobic region of the beta-AR that may represent an exo-site or an allosteric binding site.

Beta-adrenergic receptor and platelet inhibitory activities of a new series of trimetoquinol and related benzazepine analogs

1. A series of dimethoxy and methylenedioxy analogs of trimetoquinol (TMQ) and structurally related 7-membered ring benzazepines (BA) were evaluated for their pharmacological effects in beta-adrenergic (atria, trachea) and thromboxane A2/prostaglandin H2 receptor systems (aorta, platelets). 2. Results show that both the 6,7-dihydroxy (catechol) moiety of trimetoquinol and an intact tetrahydroisoquinoline nucleus are essential for maintaining potent beta-stimulating and antithromboxane A2 activities. 3. By contrast, ring enlargement, as in the BA analogs, or masking of the catechol with dimethoxy or methylenedioxy functional groups enhanced the potency of inhibitors on thromboxane A2-independent activation of human platelets induced by bacterial phospholipase C (PLC). 4. The selective blockade of this pathway by these compounds suggests that they may represent a new and novel class of antiplatelet drugs.

Pharmacological study of atypical beta-adrenoceptors in rat esophageal smooth muscle

The chemical specificity for the beta-adrenoceptor mediated relaxation of rat esophageal smooth muscle was evaluated using selective and non-selective beta-adrenoceptor agonists and antagonists. Pindolol, ICI 89,406, ICI 118551 [erythro-1-(7-methylindan-4-yloxy)-3-(isopropylamine)-but an-2-ol] and the beta-adrenoceptor alkylating agent, pindobind, produced only small rightward shifts in the concentration-response curves of (-)-isoprenaline and (-)-trimetoquinol in this preparation. Rank order potency (pD2 values) of agonists was: (+/-)-trimetoquinol [1-(3',4',5'-trimethoxybenzyl)-6,7-dihydroxy-1,2,3, 4-tetrahydroisoquinoline] (8.34) = (-)-trimetoquinol (8.26) = BRL 37344 [(R* R*)-(+/-)-4-[2'-2-hydroxy 2-(3-chlorophenyl)ethylamino]propyl] phenoxyacetic acid] (8.16) = ICID7114 [(S)-4-(2-hydroxy- 3-phenoxy-propylamino-ethoxy)-N-(2-methoxyethyl) phenoxyacetamide] (8.03) > or = (-)-isoprenaline (7.82) > 3',5'-diiodotrimetoquinol [1-(3',5'-diiodo-4'-methoxybenzyl)-6, 7-dihydroxy-1,2,3,4-tetrahydroisoquinoline] (7.28) > 3'-iodotrimetoquinol [1-(3'-iodo-4',5'-dimethoxybenzyl)-6, 7-dihydroxy-1,2,3,4-tetrahydroisoquinoline] (7.04) > ractopamine (6.84) = 5,8-difluorotrimetoquinol [5,8-difluoro-6,7-dihydroxy-1- (3',4',5'-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline] (6.82) > 8-fluorotrimetoquinol [6,7-dihydroxy-8-fluoro-1-(3',4',5'- trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline] (6.56) > or = (-)-noradrenaline (6.46) > or = (-)-adrenaline (6.36) > (+/-)-noradrenaline (6.24) > (+/-)-adrenaline (6.00) > clenbuterol (5.83) > (-)-1-benzyl-6, 7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (5.75). Isomeric activity ratios of trimetoquinol isomers [(-)-(S)- > > (+)-(R)-] in esophageal smooth muscle in the presence and absence of 1 microM pindolol were 1995- and 2951-fold, respectively; and were much greater than those in rat atria (282-fold) and rat trachea (107-fold). The atypical beta/beta 3-adrenoceptor partial agonist, ICI D7114, produced concentration-dependent rightward shifts of the concentration-response curves of (-)-isoprenaline, (-)-trimetoquinol and the reference atypical beta/beta 3-adrenoceptor agonist, BRL 37344. Schild plot analysis of ICI D7114 against trimetoquinol gave slope and pA2 values of 0.91 and of 7.9, respectively. These results clearly demonstrate that the relaxant effects of these agonists in rat esophageal smooth muscle are primarily mediated through the activation of atypical beta/beta 3-adrenoceptors. (-)-Trimetoquinol was as potent as (-)- isoprenaline and BRL 37344, and was the most stereoselective agonist evaluated in this tissue system.

Pharmacological characteristics of BDTI, a new isoquinoline-derived beta 2-adrenoceptor agonist, in canine trachea and rat heart

The tracheal relaxing effects and beta 2-selectivity of BDTI (1-benzyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline HBr) were investigated in canine trachea and rat heart by radioligand binding assay and pharmacological experiments in comparison with those of other beta-adrenoceptor agonists, salbutamol and isoprenaline. The potency of relaxing effect on carbachol-induced contraction in isolated canine trachea was in the order of isoprenaline (pD2 = 6.70 +/- 0.08) > BDTI (6.11 +/- 0.06) approximately salbutamol (6.14 +/- 0.08). ICI-118,551 (a selective beta 2-antagonist) and atenolol (a selective beta 1-antagonist) inhibited the relaxant action of BDTI with pKB values of 8.4 and 5.3, respectively, corresponding to high affinity for ICI-118,551 and low affinity for atenolol in antagonizing this response. The Kd values of radioligand ([3H]-CGP12177) were 453.3 +/- 30.8 and 563.4 +/- 96.7 pmol/l in cultured canine tracheal smooth muscle cells (TSMCs) and rat cardiomyocytes, respectively, and the Bmax values were 64.6 +/- 10.7 and 245.7 +/- 44.5 fmol/mg protein, respectively. BDTI, salbutamol and isoprenaline inhibited the binding of [3H]-CGP12177 in a concentration-dependent manner in cultured canine TSMCs (Ki 0.73 +/- 0.15, 0.75 +/- 0.21 and 0.24 +/- 0.05 mumol/l, respectively) and rat cardiomyocytes (Ki 2.76 +/- 0.36, 2.31 +/- 0.26 and 0.22 +/- 0.03 mumol/l, respectively). These results demonstrated that BDTI possessed moderate selectivity (3.8-fold) to beta 2-adrenoceptors as judged from the Ki (heart)/Ki (trachea) value (salbutamol 3.1-fold, isoprenaline 0.92-fold). BDTI and salbutamol also stimulated cAMP formation in a concentration-dependent manner in cultured canine TSMCs (EC50 0.5 +/- 0.2 and 0.4 +/- 0.1 mumol/l, respectively) and rat cardiomyocytes (EC50 6.2 +/- 0.5 and 5.7 +/- 0.6 mumol/l, respectively). The selectivity of BDTI and salbutamol for beta 2-adrenoceptors on the cAMP response were 12.4 and 14.3 times, respectively. It is concluded that BDTI is a beta 2-selective adrenoceptor agonist.

Pharmacological activities of trimetoquinol and 1-benzyl halogen-substituted analogues on rat beta-adrenoceptor subtypes

The beta-adrenoceptor activity profile of trimetoquinol and its 1-benzyl halogen-substituted analogues was studied in rat tissues containing primarily beta 1 (atria)-, beta 2 (trachea)- and atypical beta/beta 3 (distal colon and brown adipose tissue)-adrenoceptors. Functional biological activity resided in the (-)-isomer of trimetoquinol which was 112-, 275-, 372- and 513-fold more potent than (+)-trimetoquinol in trachea, right atria, distal colon and brown adipose tissue, respectively. (+/-)-Trimetoquinol was equally or slightly less active than (-)-trimetoquinol. The 1-benzyl halogen-substituted analogues of trimetoquinol exhibited differential activation of beta-adrenoceptor subtypes. In functional assays, 3'-iodotrimetoquinol was a potent activator of all beta-adrenoceptor subtypes. 3',5'-Diiodotrimetoquinol was 10-fold more potent as an agonist in tissues containing atypical beta/beta 3-adrenoceptors than those tissues containing beta 1- and beta 2-adrenoceptor sites. Furthermore, this drug was a partial agonist as compared to (+/-)-trimetoquinol and 3'-iodotrimetoquinol on beta 1-adrenoceptors. Pharmacological properties of the compounds on rat beta 3-adrenoceptors expressed in Chinese hamster ovary (CHO) cells were consistent with results observed in functional assays. 3',5'-Diiodotrimetoquinol possessed the greatest potency for activation of adenylyl cyclase. Rank order of affinity for rat beta 3-adrenoceptor was 3'-iodotrimetoquinol = 3',5'-diiodotrimetoquinol > (+/-)-trimetoquinol > (-)-isoprenaline. These results suggest that 3',5'-diiodotrimetoquinol is a promising drug for further chemical modification in the development of selective beta 3-adrenoceptor ligands.

Biochemical and pharmacological characterization of high-affinity trimetoquinol analogs on guinea pig and human beta adrenergic receptor subtypes: evidence for partial agonism

Radioligand binding assays were used to characterize the interaction of a series of trimetoquinol [1-(3',4',5'-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoqui nol ine; TMQ] analogs with beta adrenergic receptors (beta-AR). The results indicated that TMQ analogs bound with similar affinities to guinea pig (heart, lung and skeletal muscle) and human (beta-AR in Escherichia coli) beta-1- and beta-2-AR subtypes. However, the isomers of TMQ and 8-fluoro-TMQ bound stereoselectively to beta-AR with the S-isomers having affinities at least 112- and 8-fold greater, respectively, than their corresponding R-isomers. In general, a direct relationship existed between TMQ analog binding to guinea pig beta-AR and functional activity on guinea pig right atria (beta-1) and trachea (beta-2). For selected halogenated TMQ analogs (3',5'-diiodo-TMQ, 3'-iodo-TMQ, 5,8-difluoro-TMQ and 5-iodo-TMQ) which had higher beta-AR affinities than TMQ, but were less potent beta-AR agonists than TMQ, this relationship was not seen. To explain this, the function of the TMQ analogs was analyzed at the level of the beta-AR-associated effector mechanism (i.e., G-protein and adenylyl cyclase). In Chinese hamster ovary cells expressing human beta-2-AR, TMQ and halogenated analogs bound to the receptor with high affinity (nanomolar range); however, they failed to effectively couple with beta-AR-associated G-protein and only partially activated receptor-associated adenylyl cyclase. Receptor occupancies of 0.14, 2 and 23% were required for (-)-isoproterenol, S-(-)-TMQ and 3'5'-diiodo-TMQ to produce equivalent cyclic AMP accumulations in human beta-2-AR Chinese hamster ovary cells. Thus, TMQ and halogenated TMQ derivatives bind stereoselectively to beta-AR with high affinity, and may be classified as partial beta-AR agonists.

Isomeric-activity ratios of trimetoquinol enantiomers on beta-adrenergic receptor subtypes: functional and biochemical studies

Trimetoquinol [1-(3',4',5'-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4- tetrahydroisoquinoline , TMQ] exists as two enantiomers, and the (-)-(S)-isomer is a potent beta-adrenergic receptor (beta-AR) agonist. Experiments were conducted to examine the functional and biochemical potencies of the (S)-and (R)-enantiomers of TMQ for interaction with beta-AR subtypes in tissues, membrane fractions, and cell systems. The isomeric-activity ratios (IARs) of the TMQ isomers [(S)-isomer > > (R)-isomer] for stimulation of beta 1- and beta 2-AR of guinea pig right atria and trachea were 224 and 1585, respectively; these IARs were similar to those observed on atypical beta-AR systems of rat distal colon (575), rat brown adipocytes (398), but differed from that of rat esophageal smooth muscle (2884) in the presence of pindolol. In the absence of pindolol, the potencies for the TMQ enantiomers were slightly increased; however, the IARs remained unchanged in rat distal colon, rat brown adipocytes, and rat esophageal smooth muscle. Similarly, radioligand binding studies demonstrated that the TMQ isomer beta-AR affinities were stereoselective for the (-)-(S)-isomer in membranes of guinea pig left ventricle (beta 1) and lung (beta 2) giving IARs of 115 and 389, respectively; and in E. coli expressing human beta 1- and beta 2-AR giving IARs of 661 and 724, respectively. Corresponding IARs of receptor affinities and stimulation of cAMP accumulation in Chinese hamster ovary cells expressing human beta 2-AR and rat beta 3-AR were 331 and 282, and 118 and 4678, respectively. These results indicate that the (-)-(S)-isomer of TMQ exhibits high affinity, and is a potent and highly stereoselective agonist for each beta-AR subtype, that the isomers generally fail to differentiate between the beta-AR subtypes, and that, based upon differences in IAR within beta 3-AR containing systems, subtypes of atypical beta (or beta 3)-AR may exist in adipose tissue and smooth muscle.

Halogen-substituted trimetoquinol analogs as thromboxane A2 receptor antagonists in platelets and aorta

Trimetoquinol (TMQ) is a non-prostanoid compound that blocks prostaglandin H2/thromboxane A2 (TXA2) receptor-mediated responses initiated by a prostaglandin (PG) H2 analog, U46619, in human platelets and rat aorta. Ring fluorine-substituted TMQ analogs selectively antagonized PG-dependent human platelet activation induced by U46619, arachidonic acid, collagen, ADP or epinephrine; and were about 300-fold less potent as inhibitors of PG-independent responses mediated by thrombin or bacterial phospholipase C. For each inducer of the PG-dependent pathway, the rank order of inhibitory potency was identical (TMQ > 8-fluoro-TMQ > 5-fluoro- TMQ). Iodine substitution yielded a similar rank order of antagonism against U46619-induced platelet activation (TMQ > 8-iodo-TMQ > 5-iodo-TMQ), and all TMQ analogs inhibited platelet aggregation in whole blood as well as in platelet-rich plasma. Inhibition of specific [3H]SQ 29,548 binding by TMQ analogs was highly correlated with inhibition of functional responses to U46619. Radioligand binding experiments using TMQ analogs with rat platelets showed no interspecies difference in comparison with human platelets. The rank order of inhibitory potencies for the fluorinated (but not iodinated) TMQ analogs changed in rat thoracic aorta with 8-fluoro-TMQ > TMQ > or = 5-fluoro-TMQ as antagonists of U46619-induced vascular contraction. These findings demonstrate that the primary mechanism of antiplatelet action of TMQ analogs is related to a blockade of TXA2 receptor sites, and ring-halogenated TMQ analogs distinguish between TXA2-mediated functional responses in vascular smooth muscle and platelets.

Interactions of nonprostanoid trimetoquinol analogs with thromboxane A2/prostaglandin H2 receptors in human platelets, rat vascular endothelial cells and rat vascular smooth muscle cells

Trimetoquinol (TMQ), a nonprostanoid compound, inhibits thromboxane A2 agonist-induced responses in platelets and vascular smooth muscle. Sixteen TMQ analogs were used to examine the stereochemical requirements of the interaction with thromboxane A2/prostaglandin H2 (TP) receptor sites in human platelets (HP), and cultured rat vascular endothelial (RVEC) and smooth muscle (RVSMC) cells. [3H]SQ 29548 was used as the ligand for TP receptors. The receptor binding affinities of these TMQ analogs for TP receptors in HP, RVEC and RVSMC were highly correlated with each other, and to their reported inhibitory potency values against U46619-induced HP aggregation and serotonin secretion, and contraction of rat aorta. TP receptor binding affinities of TMQ and 8-fluoro TMQ isomers were highly stereoselective (R-isomer > S-isomer), and only the 8-fluoro TMQ isomers gave qualitatively different functional responses in rat aorta. The affinity of TMQ for TP receptors was increased by addition of iodine and fluorine atoms at the 5- and 8-positions of the catechol ring or by replacement of the methoxy groups with iodine atoms on the 1-benzyl ring system. The results indicate that: 1) the stereochemical requirements of TMQ analogs for interaction with TP receptors in these cell systems are the same; 2) although TMQ analogs act as TP receptor antagonists, differences in functional responses by 8-fluoro TMQ isomers in platelets and aorta are not explained by their relative binding affinities to TP receptors; and 3) asymmetric halogenated TMQ analogs should be useful as affinity probes for further characterization of TP receptors.

Selective beta 1-adrenoceptor agonist activity of denopamine and its derivatives in dogs

Cardiovascular effects of intravenously administered denopamine and its derivatives were investigated in anesthetized dogs and their positive inotropic and hypotensive effects were compared. Structure-activity relationships were examined by modifying the methoxy group in ring B and the hydroxy group in ring A in structure II, a ring-fissioned product of trimetoquinol. Almost all test compounds demonstrated positive inotropic and chronotropic effects as well as hypotensive effects which were mediated by beta-adrenoceptors. With modification of the methoxy group in ring B, only 3,4-dimethoxy, 2,3,4-trimethoxy and 3,4,5-trimethoxy derivatives exhibited beta 1-adrenoceptor selectivity. The 3,4-dimethoxy derivative showed the most potent positive inotropic effect and the highest selectivity to beta 1-adrenoceptor. By structural modification of the hydroxyl group in ring A of the 3,4-dimethoxy derivatives, the potency of positive inotropic effect was affected, while beta 1-adrenoceptor selectivity of the derivatives with 3,5-dihydroxy, 3- and 4-monohydroxy groups were essentially maintained. Among beta 1-adrenoceptor selective compounds, the dose ratios between intravenous and intraduodenal administrations of catechol derivatives like isoproterenol were higher than those of non-catechol derivatives. The 4-monohydroxy derivative (racemic denopamine) exhibited the smallest dose ratio with a long-lasting action. Thus, we could identify selective beta 1-adrenoceptor agonists by the structural modification of a selective beta 2-adrenoceptor agonist, trimetoquinol. In this group of compounds, beta-hydroxy moiety was suggested to be requisite to potent beta-adrenoceptor stimulating action and 3,4-dimethoxyphenethyl structure was important for manifestation of beta 1-adrenoceptor selectivity.

Thromboxane A2 accounts for bronchoconstriction but not for platelet sequestration and microvascular albumin exchanges induced by fMLP in the guinea pig lung

When injected i.v. to guinea pigs, the granulocyte secretagog N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induces bronchoconstriction (BC), lung platelet sequestration and increased transendothelial albumin exchanges in lungs. We evaluated BC and the variations of the lung contents in radiolabeled platelets, erythrocytes and extravascular albumin, as measurements of platelet lung entrapment, reduction of lung blood volume and increase of transendothelial albumin exchanges, respectively. Trimetoquinol, a thromboxane A2 (TXA2)-endoperoxide receptor antagonist, inhibited BC and platelet entrapment by lungs induced by fMLP, but protection was nonspecific because it also suppressed BC by histamine. The specific TXA2 synthetase inhibitor/endoperoxide receptor antagonist ridogrel suppressed BC and reduced lung platelet entrapment, but failed to prevent the increase of extravascular albumin and the decrease of erythrocyte lung contents due to fMLP. Consequently, the fMLP-induced increase of vascular albumin exchanges and reduction of lung blood volume are TXA2-independent. Aspirin prevented BC, but failed to suppress lung platelet entrapment by fMLP, indicating that in vivo platelet activation is not TXA2-dependent, even though the levels of circulating TXB2, the stable metabolite of TXA2, were increased after fMLP concomitantly with that of 6-keto-prostaglandin (PG)F1 alpha, the stable metabolite of PGI2. The ridogrel-treated animals showed reduced blood level of TXB2 and increased levels of 6-keto-PGF1 alpha after fMLP challenge. Blocking the cyclooxygenase pathway with aspirin prevented ridogrel-induced protection against lung platelet sequestration after fMLP, supporting the concept that rechanneling of arachidonate metabolism toward protective prostaglandins accounts for protection by ridogrel.

Pharmacologic antagonism of thromboxane A2 receptors by trimetoquinol analogs in vitro and in vivo

Although (-)-(S)-trimetoquinol [1-(3,4,5-trimethoxy-benzyl)- 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; TMQ] is recognized as a potent bronchodilator, (+)-(R)-TMQ is a selective antagonist of human platelet aggregation and serotonin secretion induced by thromboxane A2 (TXA2) agonists. To confirm the pharmacological actions of TMQ analogs, the interaction of the drugs with TXA2 receptors was examined in human platelets and in a mouse sudden death model. The inhibitory potencies of TMQ analogs (pIC50 values) for displacement of [3H]SQ 29,548 binding to platelets showed excellent correlation with the respective pIC50 (-log IC50) values for U46619-induced aggregation (r = 0.99, P less than 0.01) and serotonin secretion (r = 0.99, P less than 0.01) in human platelet-rich plasma and for whole blood aggregation (r = 0.99, P less than 0.01). In each system, the rank order of inhibitory potencies was rac-iodoTMQ greater than or equal to (+)-(R)-TMQ greater than rac-TMQ much greater than (-)-(S)-TMQ. Antithrombotic effects of TMQ analogs were evaluated in a mouse sudden death model. In vivo antithrombotic potencies of these compounds were consistent with the in vitro potencies as TXA2 receptor antagonists in platelet systems. Administration of rac-iodoTMQ, (+)-(R)-TMQ and rac-TMQ 15 min before the injection of U46619 (800 micrograms/kg, iv) protected mice against U46619-induced sudden death. On the other hand, (-)-(S)-TMQ did not protect animals against death. Protection of U46619-induced cardiopulmonary thrombosis by TMQ analogs was seen at doses of 3-100 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological properties of novel bicyclic isoquinoline analogs in isolated guinea pig atria, trachea and in human platelets: relationship to trimetoquinol

1. Antiplatelet and beta-adrenoceptor activities of a set of secondary and tertiary N-methyl substituted amine analogs of trimetoquinol (TMQ, I and II, respectively) and 5,8-ethano-l-(p-methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquin oline (bicyclic isoquinoline compounds III and IV, respectively) were examined. 2. Compounds III and IV induced relaxations of guinea pig trachea which were blocked by propranolol whereas neither compound acted as an agonist nor antagonist of beta-adrenoceptors (chronotropy) in guinea pig atria. TMQ analogs (I and II) were agonists in both beta-adrenoceptor systems. 3. When tested in human platelets, compounds III and IV, like the TMQ analogs, blocked several inducers of the prostaglandin-dependent and -independent pathways, and the alpha 2-adrenoceptor-mediated pathway of platelet activation. 4. The bicyclic isoquinoline analogs (III and IV) possessed more selective beta 2-adrenoceptor stimulatory activity and equal or greater inhibitory activity against inducers of the prostaglandin-independent pathways of platelet function than the corresponding TMQ analogs (I and II). 5. These chemically novel lipophilic bicyclic compounds provide a new lead to the development of agents useful for the treatment of asthma and thrombotic disorders.

Pharmacological evaluation of the beta-adrenoceptor agonist and thromboxane receptor blocking properties of 1-benzyl substituted trimetoquinol analogues

The beta 1- and beta 2-adrenoceptor agonist and thromboxane A2 (TXA2) antagonist properties of trimetoquinol (TMQ, I) and 1-benzyl substituted TMQ analogues [3'-iodo-4',5'-dimethoxy TMQ, II; 3',5'-diiodo-4'-dimethoxy TMQ, III; 3',4'-dimethoxy-5'-nitro TMQ, IV; 3',4'-dimethoxy-5'-amino TMQ; V; and 3',4'-dimethoxy TMQ, VI] were studied in guinea pig atria (beta 1) and trachea (beta 2), and in rat thoracic aorta and human platelets, respectively. The rank order of agonist activities in beta 1- and beta 2-adrenoceptor tissues was IV greater than or equal to I greater than II greater than V greater than III greater than VI and I greater than II = IV = V greater than VI greater than III, respectively. An increase of beta 2/beta 1-selectivity (2- to 3-fold) was observed for analogues V and VI as compared to TMQ. The rank order of inhibitory potency against U46619-induced contraction of rat aorta and human platelet aggregation and secretion was the same (I = II = III greater than IV greater than V greater than VI). The results show that varying the substituents at the 3'- and 5'-positions of the trimethoxybenzyl group of TMQ produces compounds which give different profiles of biological activity for beta-adrenoceptor agonism versus TXA2 antagonism. Certain TMQ analogues, notably analogue V, showed a greater selectivity as beta 2-receptor agonists and TXA2 antagonists in vascular smooth muscle than the parent drug (TMQ), and the iodinated analogues (II and III) have promise as potential radioligands or photoaffinity probes for thromboxane A2 receptors.

Effects of thromboxane A2 on thoracic aorta of young and old rats: use of selective thromboxane receptor antagonists

Thromboxane A2 (TXA2) is a bioactive metabolite of arachidonic acid which produces vascular smooth muscle contraction and blood platelet aggregation. The goal of this study is to establish whether there are age-dependent differences of vascular contractility to TXA2. Thoracic aorta of F-344 rats of age 4-6 months (young) and 22-23 months (old) were used as a model to examine responses to U46619 [(15S)-hydroxy-11 alpha, 9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid; a TXA2 agonist] alone or in the presence of prostanoid (SQ 29,548) or nonprostanoid (trimetoquinol, TMQ) endoperoxide/TXA2 receptor antagonists. Maximal contractile responses (84 and 89% relative to KCl) and EC50 values (23 and 55 nmol/l, respectively) to U46619 were the same in aortic strips of young and old animals. Experimentally determined pA2 and pKB values for SQ 29,548 and TMQ as antagonists of U46619-mediated contraction were unchanged in aorta of young (9.09 and 5.83, respectively) and old (9.41 and 6.10, respectively) rats. We conclude that the reactivity and population of TXA2 receptors in rat vascular smooth muscle are unaffected by the aging process.

Characterization of the inhibition of U46619-mediated human platelet activation by the trimetoquinol isomers. Evidence for endoperoxide/thromboxane A2 receptor blockade

Sites of inhibition for the trimetoquinol (TMQ) isomers on 15S-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z,13E-dienoic acid (U46619)-, 12-O-tetradecanoylphorbol 13-acetate (TPA)- and A23187-induced human platelet activation were investigated. Experiments using washed human platelets were designed to characterize relationships among functional (aggregation, secretion) and biochemical (protein phosphorylation, metabolism of inositol phospholipids and radioligand displacement analysis) processes of platelet activation by U46619 and the specificity of inhibition by the TMQ isomers. Thromboxane A2 receptor stimulation by U46619 in human platelets resulted in a time- and concentration-dependent breakdown of inositol phospholipids [phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-monophosphate (PIP), and phosphatidylinositol (PI)], phosphatidic acid (PA) accumulation, phosphorylation of 20 and 45 kD proteins, aggregation and serotonin secretion. The TMQ isomers stereoselectively inhibited all U46619-mediated platelet activation processes. R(+)-TMQ was 40- and 22-fold more potent than S(-)-TMQ as an inhibitor of U46619-induced platelet aggregation and serotonin secretion respectively. In addition, R(+)-TMQ blocked U46619-induced 20 kD protein phosphorylation, 45 kD protein phosphorylation, PIP2, PIP and PI breakdown, and PA accumulation with a potency which was 8-, 13-, 45-, 37-, 33- and 33-fold greater than the S(-)-isomer respectively. In contrast to S(-)-TMQ, R(+)-TMQ produced a concentration-dependent inhibition of specific [3H]U46619 binding to endoperoxide/thromboxane A2 receptor sites in washed platelets. In other experiments, S(-)-TMQ was more potent than R(+)-TMQ as an inhibitor of TPA- and A23187-induced platelet aggregation and serotonin secretion, and of TPA-induced phosphorylation of 45 and 20 kD proteins. The inhibitory potencies of S(-)-TMQ against TPA- or A23187-induced responses were similar to those needed for antagonism of U46619-mediated platelet activation. In contrast, much higher concentrations of R(+)-TMQ were required for blockade of TPA or A23187 versus U46619-mediated responses in human platelets. Taken collectively, the data show that the TMQ isomers interfered with the endoperoxide/thromboxane A2 receptor-mediated phospholipase C-signal cascade of inositol phospholipid hydrolysis, calcium mobilization, and protein phosphorylation leading to platelet aggregation and secretion. R(+)-TMQ acted as a pharmacologically selective and highly stereospecific [R(+)-TMQ much greater than S(-)-TMQ] antagonist of endoperoxide/thromboxane A2 receptor sites in platelets.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of compound IS-35 on intraocular pressure

The influence of compound IS-35 on intraocular pressure of unanesthetized rabbits was studied. In some cases intraocular pressure was measured with either the tonometer of Schiotz and was calculated in mmHg according to Leydhecker's scale (1973), or with the tonometer of Maclakov. Intraocular pressure was measured before and at 30, 60, 120, 180, 240 and 360 min after topical application of IS-35, timolol and trimetoquinol. It was established that IS-35 applied locally in the eye as 0.5% solution or collyrium decreases statistically significantly intraocular pressure. This effect was similar to that of timolol and exceeded significantly the effect of trimetoquinol. The experimental study on the beta-adrenergic adenylate cyclase showed that the mechanism of action of IS-35 on ophthalmotonus most probably is similar to the effect of timolol and is due to the suppression of aqueous humor formation.

Pharmacological evaluation of the beta-adrenoceptor agonist and thromboxane antagonist properties of N-substituted trimetoquinol analogues

The beta 1- and beta 2-adrenoceptor agonist and U46619 (a thromboxane A2 agonist) antagonist properties of trimetoquinol (TMQ, I) and its optical isomers, and N-substituted TMQ analogues (methyl, II; 2-hydroxyethyl, III; cyclic sulfite N-2-chloroethyl, IV; 2-chloroethyl, V; benzyl, VI) were studied in guinea pig atria and trachea and rat aorta, respectively. All compounds gave concentration-dependent responses in atria and trachea, and the rank order of beta-adrenoceptor agonist potency was I greater than II greater than III greater than IV greater than V greater than VI. Whereas N-substitution reduced potency for beta-agonism, the beta 2/beta 1-selectivity ratio was enhanced by increasing the size of the N-substituent. All analogues possessed equal or greater (up to 41-fold more) beta 2-selectivity than I. Propranolol was a competitive antagonist of selected TMQ analogues in guinea pig trachea and atria, thus confirming the beta-adrenoceptor actions of these drugs. The optical isomers of TMQ gave a rank order of agonist potency of S(-)-TMQ greater than R(+)-TMQ, and a beta 2/beta 1-selectivity equal to or greater than racemic-TMQ. Each TMQ analogue also blocked the contractile responses of U46619 in rat aorta in a competitive manner, and the rank order of inhibition of U46619-induced contraction in rat aorta was I greater than VI greater than II = III greater than IV greater than V. N-Benzyl TMQ (VI) possessed the greatest potency for U46619 blockade and beta 2/beta 1-selectivity ratio of the N-substituted analogues. The results show that varying the N-substituents on TMQ produces compounds which retain beta 2-selectivity and give a different activity profile for beta-adrenoceptor activation vs. endoperoxide/thromboxane A2 antagonism.

5-fluoro- and 8-fluorotrimetoquinol: selective beta 2-adrenoceptor agonists

The 5-fluoro and 8-fluoro analogues of trimetoquinol, TMQ, have been synthesized and evaluated for beta 2- and beta 1-adrenoceptor activity in guinea pig trachea and atria, respectively. The fluoro analogues of TMQ maintained potent beta 2-adrenoceptor agonist activity but had reduced beta 1-adrenoceptor agonist activity. The changes in beta 1-activity of these compounds were correlated to differences in phenolic pKa's. The beta 1- and beta 2-adrenoceptor actions of 2 and 3 were blocked in a competitive manner by propranolol. The enhanced beta 2/beta 1 selectivity for the analogues was found to be 8-fluoro analogue 3 greater than 5-fluoro analogue 2 greater than trimetoquinol (1).

6,7-Dichloro-1-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline . A structurally novel beta-adrenergic receptor blocking agent

Replacement of the catecholic hydroxyl groups of the beta-adrenergic receptor agonist 6,7-dihydroxy-1-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline (trimetoquinol) with chloro substituents results in a compound with marked beta-adrenoceptor antagonist properties. This, therefore, parallels the similar transformation of the beta-adrenoreceptor agonist isoproterenol into the antagonist dichloroisoproterenol. In a test for inhibition of isoproterenol-induced enhancement of the rate of contraction of spontaneously beating guinea pig atrial pairs the resultant 6,7-dichloro-1-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline (6b) had a KB value of (6.7 +/- 2.3) X 10(-8) M. Although this is nearly 2 orders of magnitude less potent than propranolol (KB = 6.2 X 10(-10) M in this test), this compound represents the prototype of a new class of beta-adrenergic receptor blockers, and unlike dichloroisoproterenol it is not a partial agonist. It has physicochemical properties, e.g., pKa and distribution and partition coefficients, that differ from the prototypic beta-blockers. These altered properties might impart advantageous tissue distribution and altered pharmacological properties to the new molecule. This new beta-adrenoreceptor antagonist is suggested to merit further study.

Syntheses and beta-adrenergic agonist and antiaggregatory properties of N-substituted trimetoquinol analogues

Trimetoquinol [1-(3,4,5-trimethoxybenzyl)-6,7- dihydroxy-1,2,3,4-tetrahydroisoquinoline, TMQ] is a potent beta-adrenergic receptor agonist and inhibitor of human platelet aggregation. Selective cleavage of O-benzyl groups in the presence of an N-benzyl group using HCl and formation of a cyclic sulfite ester from the reaction of a catechol with thionyl chloride were achieved. The N-substituents included methyl, benzyl, and beta-hydroxy- and beta-chloroethyl groups. Each N-substituted TMQ caused a concentration-dependent stimulation of beta 2 (trachea) and beta 1 (atria) adrenoceptor tissues and inhibition of 15(S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13(E)-dienoic acid (U46619, a thromboxane A2 mimetic) mediated human platelet activation. TMQ remained the most potent in the series. Structure-activity results indicated that the larger the N-substituent, the lower the beta-adrenergic activity but the higher the inhibition of platelet aggregatory activity. Thus, the structural requirements of these TMQ analogues for the two types of biological activity are different.

Activation of NADPH-oxidase by arachidonic acid involves phospholipase A2 in intact human neutrophils but not in the cell-free system

The mechanism involved in the stimulation of NADPH-oxidase by arachidonic acid (AA) in intact human neutrophils was studied and compared with that involved in a cell-free system. [3H]-AA was released from pre-labeled cells upon AA stimulation, and phospholipase A2 inhibitors reduced in parallel the release of [3H]-AA and superoxide. Cyclooxygenase, lipoxygenase or protein kinase inhibitors failed to affect either response. In a cell-free system, no release of [3H]-AA was observed after AA addition, whereas NADPH-oxidase was activated; the generation of superoxide was not inhibited by phospholipase inhibitors and was not initiated by adding phospholipase A2 to the preparation. Thus AA stimulates NADPH-oxidase through a phospholipase A2 mediated pathway in intact cells, but activates the oxidase independent of phospholipase A2 in a broken cell system, suggesting distinctive mechanisms of activation for each system.

Synthesis and investigation of the beta-adrenoceptor agonist and platelet antiaggregatory properties of 1,7,8-trisubstituted 2,3,4,5-tetrahydro-1H-2-benzazepine analogues of trimetoquinol

The synthesis and biological evaluation of 7,8-dihydroxy (2) and 7,8-methylenedioxy (3) analogues of 1-[(3,4,5-trimethyoxyphenyl)methyl]-2,3,4,5-tetradhyo-1H-2-b enzazepine on beta-adrenoceptor systems and human platelets were undertaken and compared with trimetoquinol (TMQ, 1). Whereas 1 is a potent beta-adrenoceptor agonist in guinea pig atria and trachea (pD2 = 8.2), analogue 2 was marginally effective at relaxing guinea pig tracheal smooth muscle (pD2 = 4.4) and inactive as an agonist on guinea pig atria. Analogues 2 and 3 were inhibitors of phospholipase C (PLC; from Clostridium perfringens) induced and secondary wave of ADP-induced aggregation responses and inactive against low-dose thrombin-induced or stable endoperoxide (U46619) induced human platelet aggregation. Against ADP-induced serotonin secretion, 3 was 9-fold more active than analogue 2. Further, the rank order of TMQ isomers and 3 as inhibitors of PLC-induced platelet aggregation, serotonin secretion, and phosphatidylinositol degradation was identical (3 greater than (S)-(-)-1 greater than (R)-(+)-1). The results suggest that these compounds are blocking the action of PLC by interfering with phosphatidylinositol turnover in platelet membranes. The inhibition of ADP-induced responses in human platelets by analogues 2 and 3 also suggests a site of inhibition at a level of arachidonic acid release. Thus, ring expansion of 1 as in the benzazepine analogues 2 and 3 has allowed us to develop selective inhibitors of platelet function that lack significant beta-adrenoceptor activity.

The effects of trimetoquinol on the intact rabbit heart and myocardial adenylate cyclase activity: evidence for spare myocardial beta receptors

We have compared and contrasted the actions of (-)isoproterenol and (+/-) trimetoquinol on rabbit heart preparations. In the presence of either GTP or Gpp[NH]p (guanosine-5'-(beta, gamma imino) triphosphate), trimetoquinol displayed partial agonist activity in stimulating adenylate cyclase activity in a particulate rabbit heart preparation. Trimetoquinol enhanced adenylate cyclase activity 20% or 65% of the maximum obtainable by isoproterenol in the presence of GTP or Gpp[NH]p respectively. In the presence of GTP, concentrations of catecholamines required to enhance cyclase activity 15% of the maximum obtainable with isoproterenol (EC15) were 2.0 X 10(-7) M and 5.5 X 10(-8) M for trimetoquinol and isoproterenol, respectively. In the presence of Gpp[NH]p EC30 values were 2.0 X 10(-7) and 3.5 X 10(-8) M for trimetoquinol and isoproterenol respectively. Trimetoquinol also displayed partial agonist activity for the ability to increase cAMP levels in the isolated perfused rabbit heart. By contrast trimetoquinol was equieffective to isoproterenol at increasing tension development and rate of contraction of the isolated perfused heart. Concentrations of catecholamines required to increase tension and rate of contraction 50% of the maximum obtainable with isoproterenol were 1.5 X 10(-7) M and 1.7 X 10(-8) M for trimetoquinol and isoproterenol, respectively. These data show that only a partial stimulation of adenylate cyclase activity and cAMP levels by trimetoquinol is sufficient to produce maximal changes in mechanical activity of the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of trimetoquinol analogs for antagonism of endoperoxide/thromboxane A2-mediated responses in human platelets and rat aorta

The pharmacological properties of a limited series of tetrahydro-isoquinoline [trimetoquinol (TMQ)] analogs for inhibition of endoperoxide (U46619)-mediated responses in human platelets and rat aorta were examined. All analogs blocked U46619-induced aggregatory and secretory responses in platelets, and contraction of rat aorta in a concentration-dependent manner. R-(+)-TMQ was a competitive-type inhibitor of U46619-induced contractions of rat aorta. The relative inhibitory potency for TMQ analogs against U46619-induced effects was TMQ greater than N-methyl TMQ greater than or equal to erythro-alpha-methyl TMQ greater than threo-alpha-methyl TMQ greater than or equal to alpha-dimethyl TMQ. R-(+)-TMQ and the azoprostanoid analog (U51605) were potent antagonists of U46619 action in rat aorta with pA2 values of 5.97 and 5.70, respectively. Other experiments indicated that U51605 was a partial agonist and R-(+)-TMQ was an inhibitor of U51605-induced contractions of rat aorta (pKB = 5.94). R-(+)-TMQ also blocked prostaglandin E2-mediated responses in rat aorta (pA2 = 5.46) but was ineffective as an antagonist of prostaglandin F2 alpha and LTD4 responses in dog iris sphincter and guinea-pig trachea or lung parenchyma, respectively. The data indicate that 1) the TMQ analogs were antagonists of endoperoxide/thromboxane A2-mediated responses in rat aorta and human platelets involving a similar mechanism of action and 2) stereochemical requirements of these TMQ analogs for activation of beta adrenoceptors and antagonism of endoperoxide/thromboxane A2-mediated responses are different. It is concluded that selectivity for these two pharmacological properties of TMQ can be achieved by appropriate stereochemical modification of the tetrahydroisoquinoline nucleus.

Blood platelet function, medicinal agents, and other chemical entities

An overview is presented on blood platelet function, including the interaction of platelets with the vessel wall and with medicinal agents and related chemical entities. Current interpretations are discussed in terms of the most recent biological, chemical, and physicochemical concepts.

Human platelet activation by bacterial phospholipase C is mediated by phosphatidylinositol hydrolysis but not generation of phosphatidic acid: inhibition by a selective inhibitor of phospholipase C

We have shown earlier that phospholipase C (PLC) from Clostridium perfringens causes human platelet aggregation and secretion in a concentration dependent manner. The present study was undertaken to further characterize the specificity of the effects of PLC and to better understand the mechanism of the action of this inducer. A methylene-dioxybenzazepine (MDBA) analog of trimetoquinol was synthesized and tested for antiplatelet activity. MDBA (3-30 microM) inhibited PLC-induced aggregation in a concentration dependent manner. Whereas up to 200 microM MDBA did not inhibit aggregation induced by either thrombin, arachidonic acid, or U46619. Effects of PLC (0.05 U/ml) on hydrolysis of phosphatidylinositol, production of phosphatidic acid and thromboxane B2 (TXB2) synthesis were investigated using [32P]-phosphate and [14C]-arachidonic acid labeled platelets. PLC (0.05 U/ml) caused a time dependent decrease in platelet phosphatidylinositol. Up to 50% of labeled phosphatidylinositol was lost from platelets in five minutes. MDBA (3-30 microM) inhibited PLC-induced loss of phosphatidylinositol in a concentration dependent manner. An increase in phosphatidic acid was also observed in PLC-stimulated platelets. Up to 100 microM MDBA did not inhibit production of phosphatidic acid. PLC-treated platelets did not produce any TXB2. In other experiments possible protease contamination of PLC preparations was tested by incubating PLC (0.03-0.5 U/ml) with [14C]-casein. PLC in concentrations up to ten times higher than the concentrations used in aggregation studies did not cause hydrolysis of [14C]-casein, whereas more than 30% of [14C]-casein was hydrolyzed by trypsin. PLC-induced aggregation was not inhibited by up to 300 microM adenosine or ATP. In other experiments, platelet aggregation by ADP was inhibited by adenosine and ATP in a concentration dependent manner. The addition of calcium (0.5- 2.0 mM) increased aggregation by PLC in a concentration dependent manner. These findings suggest that PLC-induced activation of platelets is: (a) dependent on phosphatidylinositol hydrolysis but not on the production of phosphatidic acid, TXB2 or secretion of ADP; (b) not caused by protease contaminants; (c) calcium dependent; and (d) MDBA inhibits PLC-induced aggregation by blocking phosphatidylinositol hydrolysis.

Electron transfer through the isolated mitochondrial cytochrome b-c1 complex

(1) A kinetic analysis of electron donation into and through the cytochrome b-c1 complex isolated from bovine heart mitochondria has been undertaken, using trimethoquinol as the donor. (2) Rate constants of two routes of redox equilibration with quinols have been defined by kinetic measurements and with the use of the inhibitors antimycin A and myxothiazol. (3) A model of electron transfer based upon the original Q-cycle formulation is presented to explain these and related results.

Bronchoselective actions of a new series of trimetoquinol analogues

In selected beta 1- (guinea pig atrial) and beta 2- (guinea pig trachea and lung parenchyma) adrenoceptor systems, we have examined the interaction of isoproterenol (ISO), trimetoquinol (TMQ), erythro- and threo-diastereoisomers of 1-(3,4,5-trimethoxy-alpha-methylbenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (alpha-methylTMQ), alpha-dimethylTMQ, N-methylTMQ and N-[2-methyl-2-(3,4,5-trimethoxyphenyl)propyl]dopamine (open chain dimethylTMQ analogue). The rank order of potency for agonists in trachea was threo-alpha-methylTMQ greater than (+/-)-TMQ greater than ISO greater than erythro-alpha-methylTMQ greater than N-methylTMQ greater than alpha-dimethylTMQ. Only N-methylTMQ gave an intrinsic activity similar to ISO, whereas the alpha-methylated TMQ analogues were partial agonists in this beta 2-system. In atria, the rank order of beta 1-potency was ISO greater than (+/-)-TMQ greater than threo-alpha-methylTMQ greater than N-methylTMQ = erythro-alpha-methylTMQ. Maximal chronotropic effects of all compounds, with the exception of threo-alpha-methylTMQ, were similar to ISO in this preparation. Both alpha-dimethylTMQ and open chain dimethylTMQ analogues were inactive as agonists in this beta 1-system. The ratio of beta 2 : beta 1 selectivity (trachea vs. atria), relative to ISO for threo-alpha-methylTMQ, erythro-alpha-methylTMQ, TMQ and N-methylTMQ was 106.5, 27, 7 and 5.8, respectively. Whereas the rank order of potency for selected compounds in lung parenchyma was ISO greater than threo-alpha-methylTMQ = TMQ greater than erythro-alpha-methylTMQ, the comparative beta 2-selectivity (lung parenchyma vs. atria) relative to ISO, for erythro-alpha-methylTMQ, threo-alpha-methylTMQ and TMQ was 2.5, 1.9 and 0.24, respectively. It is concluded that lipophilic substitutions on the alpha-carbon of the 1-(3,4,5-trimethoxybenzyl)-substituent of TMQ can generate compounds which are potent bronchoselective adrenoceptor agonists. Threo-alpha-methylTMQ and erythro-alpha-methylTMQ were more beta 2-selective than (+/-)-TMQ.

[Effect of beta adrenergic receptor agonists and blockaders on the action of bradykinin]

A study was made of the effect of beta-adrenomimetics (isoprenaline, orciprenaline, inoline) and beta-adrenoblockers (propranolol, pindolol, oxprenolol, atenolol and practolol) on changes in the tone of smooth muscles of an isolate ileum of guinea-pigs, increase in microvascular permeability and depressor reaction in rats induced by bradykinin. beta-Adrenomimetics decreased spasmogenic and microcirculatory effects of bradykinin. Depending on the selectivity and presence of partial agonistic activity, beta-adrenoblockers exerted different influence on changes in the tone of extravasal muscles and permeability induced by bradykinin. In doses of 0.1, 0.5 and 1 mg/kg (intravenously) beta-adrenoblockers potentiated and prolonged the depressor effect of bradykinin.

Selective and potent beta 2-adrenoceptor agents within the tetrahydroisoquinoline class: effect of methyl substitution at the benzylic carbon of the 1-(3,4,5-trimethoxybenzyl) group of trimetoquinol

A systematic series of methyl (2 and 3) and dimethyl (4) analogues of trimetoquinol (1) were synthesized and evaluated for their beta 1 (atria) and beta 2 (trachea) and adrenoceptor activities. Structural assignments for the erythro (2) and the threo (3) diastereoisomers of 1-(3,4,5-trimethoxy-alpha-methylbenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline were based on NMR spectra of the 6,7-dibenzyl precursors 15 and 16, respectively, and on the synthetic derivatives of cis- and trans-13-methyl-2,3-bis(benzyloxy)-9,10,11-trimethoxytetrahydroprotoberberine (18 and 17). The rank order of beta 2-agonist activity for these compounds was 3 greater than 1 greater than 2 greater than 4. The rank order of activity as beta 1 agonists on the guinea pig atria is 1 greater than 3 greater than 2, and 4 was inactive. The methylated analogues show selectivity for beta 2 receptors in our preliminary pharmacological studies. The threo isomer 3 is the most potent and selective beta 2 stimulant reported to date in the tetrahydroisoquinoline class.

Insulin release by trimetoquinol in normal and asthmatic subjects

The existence of beta 2-adrenergic receptor in pancreatic beta-cell was evaluated. Significantly low beta 2-stimulant responsiveness of pancreatic beta-cell was observed in continuously medicated and active asthmatic subjects, indicating beta-adrenergic blockade state. This low responsiveness recovered in the inactive stage of asthma and with hydrocortisone treatment.

Comparative heart rate effects of oral administration of bitolterol, terbutaline and trimetoquinol in unanesthetized dogs

Effect of a clinical dose of bitolterol, a new oral bronchodilator via adrenergic beta-receptor, on heart rate was compared with those of terbutaline and trimetoquinol in unanesthetized dogs. Oral administration of bitolterol, terbutaline and trimetoquinol increased the heart rate. The heart rate effect of bitolterol was significantly weaker than those of terbutaline and trimetoquinol.

Synthesis, beta-adrenergic activity, and platelet antiaggregatory activity of a positional isomer of trimetoquinol: 1-(2',4',5'-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4,-tetrahydroisoquinoline

A positional isomer of trimetoquinol (1), 1-(2',4',5'-trimethoxybenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (3), was synthesized and found to possess less beta-adrenergic activity than 1 in isolated guinea pig atrial and tracheal preparations. The analogue 3 was an effective antiaggregatory agent in human and rabbit platelet-rich plasma preparations, while 1 was effective only as an inhibitor of arachidonic acid induced aggregation in human platelets. These findings indicate that both qualitative and quantitative differences in biological activity have occurred as a result of changing the position of the methoxy groups on the 1-benzyl substituent of 1.

Antagonism of prostanoid-induced contractions of rat gastric fundus muscle by SC-19220, sodium meclofenamate, indomethacin or trimethoquinol

1 The effects of SC-19220, sodium meclofenamate, indomethacin or trimethoquinol were studied on contractions of the rat stomach longitudinal muscle to prostaglandin D2 (PGD2), PGE2, PGF2 alpha, PGH2, epoxymethano PGH2 analogues, PGI2, 6-keto-PGF1 alpha, 6,15-diketo-PGF1 alpha and thromboxane B2. All the drugs reduced contractions to all the prostanoids, but the degree of reduction differed widely. Selectivity of blockade was assessed by comparison with acetylcholine (ACh). 2 With SC-19220 5 micrograms/ml the effect on thromboxane B2, PGD2 or PGH2 and its epoxymethano analogues was not significantly different from the small effect on ACh, but the other prostanoids were blocked to greater extents. 3 The effect of the cyclo-oxygenase inhibitor sodium meclofenamate, 1 or 2 micrograms/ml, on 6,15-diketo-PGF1 alpha or thromboxane B2 was similar to the small antagonism of ACh, whereas the other prostanoids were blocked to greater extents. Indomethacin, 1 microgram/ml, also reduced contractions to the prostanoids, but antagonism of the PGH2 epoxymethano analogues was considerably less than with meclofenamate. 4 The beta-adrenoceptor stimulant trimethoquinol, 50 ng/ml, was the most potent prostanoid antagonist tested; all the prostanoids except PGE2 were antagonized more than ACh.

Actions of the novel bronchodilator, trimetaquinol, on bovine pulmonary vein

The actions of the beta-sympathomimetic bronchodilator trimetaquinol (TMQ) were examined on bovine pulmonary vein smooth muscle in vitro. TMQ partially and reversibly inhibited 5-hydroxytryptamine (5HT) induced contractions of the vein strips. The relaxant activity was neither blocked by propranolol (10(-7) M) nor enhanced by phentolamine (10(-7) M). Isoproterenol, alone or in the presence of phentolamine (10(-7) M), was much less effective than TMQ in relaxing 5HT-induced contractions. From these results it is suggested that TMQ functions via a "non-beta-adrenergic" mechanism to relax bovine pulmonary vein smooth muscle.