Condensed bridgehead nitrogen heterocyclic system: synthesis and pharmacological activities of 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole derivatives of ibuprofen and biphenyl-4-yloxy acetic acid

Several 3,6-disubstituted-1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazoles were prepared by condensation of 4-amino-5-substituted-3-mercapto-(4H)-1,2,4-triazoles (3a,b) with various substituted aromatic acids and aryl/alkyl isothiocyanates through a one-pot reaction. These compounds were investigated for their anti-inflammatory, analgesic, ulcerogenic, lipid peroxidation, antibacterial and antifungal activities. Some of the synthesized compounds showed potent anti-inflammatory activity along with minimal ulcerogenic effect and lipid peroxidation, compared to those of ibuprofen and flurbiprofen. Some of the tested compounds also showed moderate antimicrobial activity against tested bacterial and fungal strains.

Estimation of agonist activity at G protein-coupled receptors: analysis of M2 muscarinic receptor signaling through Gi/o,Gs, and G15

We developed novel methods for analyzing the concentration-response curve of an agonist to estimate the product of observed affinity and intrinsic efficacy, expressed relative to that of a standard agonist. This parameter, termed intrinsic relative activity (RA(i)), is most applicable for the analysis of responses at G protein-coupled receptors. RA(i) is equivalent to the potency ratios that agonists would exhibit in a hypothetical, highly sensitive assay in which all agonists behave as full agonists, even those with little intrinsic efficacy. We investigated muscarinic responses at the M(2) receptor, including stimulation of phosphoinositide hydrolysis through G(alpha15) in HEK 293T cells, inhibition of cAMP accumulation through G(i) in Chinese hamster ovary (CHO) cells, and stimulation of cAMP accumulation through G(s) in CHO cells treated with pertussis toxin. The RA(i) values of carbachol, oxotremorine-M, and the enantiomers of aceclidine were approximately the same in the three assay systems. In contrast, the activity of 4-[[N-[3-chlorophenyl]carbamoy]oxy-2-butynyl]trimethylammonium chloride (McN-A-343) was approximately 10-fold greater at M(2) receptors coupled to G(alpha15) in HEK 293T cells compared with M(2) receptors coupled to G(i) in the same cells or in CHO cells. Our results show that the RA(i) estimate is a useful measure for quantifying agonist activity across different assay systems and for detecting agonist directed signaling.

Muscarine activates the sodium-calcium exchanger via M3receptors in basal forebrain neurons

Neurons of the medial septum/diagonal band of Broca (MSDB) project to the hippocampus. Muscarinic cholinergic mechanisms within the MSDB are potent modulators of hippocampal functions; intraseptal scopolamine disrupts and intraseptal carbachol facilitates hippocampus-dependent learning and memory tasks, and the associated hippocampal theta rhythm. In earlier work, we demonstrated that, within the MSDB, the septohippocampal GABAergic but not cholinergic neurons are the primary target of muscarinic manipulations and that muscarinic activation of septohippocampal GABAergic neurons is mediated directly via M(3) receptors. In the present study, we examined the ionic mechanism(s) underlying the excitatory actions of muscarine in these neurons. Using whole-cell patch-clamp recording techniques in rat brain slices, we demonstrated that M(3) receptor-mediated muscarinic activation of MSDB neurons is dependent on external Na(+) and is also reduced by bath-applied Ni(2+) and KB-R7943 as well as by replacing external Na(+) with Li(+), suggesting a primary involvement of the Na(+)-Ca(2+) exchanger. We conclude that the M(3) receptor-mediated muscarinic activation of MSDB septohippocampal GABA-type neurons, that is important for cognitive functioning, is mediated via activation of the Na(+)-Ca(2+) exchanger.

Phenoxybenzamine and benextramine, but not 4-diphenylacetoxy-N-[2-chloroethyl]piperidine hydrochloride, display irreversible noncompetitive antagonism at G protein-coupled receptors

Many irreversible antagonists have been shown to inactivate G protein-coupled receptors (GPCRs) and used to study agonists and spare receptors. Presumably, they bind to primary (agonist) binding sites on the GPCR, although noncompetitive mechanisms of antagonism have been demonstrated but not thoroughly investigated. We studied noncompetitive antagonism by phenoxybenzamine and benextramine at alpha(2A)-adrenoceptors in stably transfected Chinese hamster ovary cells, benextramine and 4-diphenylacetoxy-N-[2-chloroethyl]piperidine hydrochloride (4-DAMP mustard) at endogenous muscarinic acetylcholine (mACh) receptors in human neuroblastoma SH-SY5Y cells, and benextramine at serotonin 5-HT(2A) receptors in stably transfected SH-SY5Y cells. Primary binding sites were protected by reversible competitive antagonists during pretreatment with irreversible antagonists. We conducted appropriate radioligand binding assays by measuring remaining primary binding sites and agonist affinity, functional assays to evaluate agonist-induced responses, and constitutive guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS)-Galpha(o) binding assays to determine remaining G protein activity. Phenoxybenzamine (100 microM; 20 min) and benextramine (10 or 100 microM; 20 min) at alpha(2A)-adrenoceptors, but not 4-DAMP mustard (100 nM; 120 min) at mACh receptors, displayed irreversible noncompetitive antagonism in addition to their known irreversible competitive antagonism. Although agonist binding affinity is not influenced, signal transduction is modulated in a G protein-dependent manner via allotopic interactions. Benextramine noncompetitively inhibits agonist-induced responses at three different GPCR types (alpha(2A), mACh, and 5-HT(2A) receptors) that signal via three families of G proteins (G(i/o), G(s), and G(q/11)). We conclude that, where irreversible antagonists are utilized to study drug-receptor interaction mechanisms, the presence of significant irreversible noncompetitive antagonism may influence the interpretation of results under the experimental conditions used.

The M2 muscarinic receptor mediates contraction through indirect mechanisms in mouse urinary bladder

We investigated the contractile role of M2 muscarinic receptors in mouse urinary bladder. When measured in the absence of other agents, contractions elicited to the muscarinic agonist oxotremorine-M exhibited properties consistent with that expected for an M3 response in urinary bladder from wild-type and M2 knockout (KO) mice. Evidence for a minor M2 receptor-mediated contraction was revealed by a comparison of responses in M3 knockout and M2/M3 double knockout mice. Treatment of wild-type and M2 knockout urinary bladder with N-2-chloroethyl-4-piperidinyl diphenylacetate (4-DAMP mustard) caused a large inhibition of the muscarinic contractile response. The residual contractions were much smaller in M2 knockout bladder compared with wild type, suggesting that M2 receptors rescue the muscarinic contractile response in wild-type bladder following inactivation of M3 receptors with 4-DAMP mustard. When measured in the presence of prostaglandin F2alpha and isoproterenol or forskolin, oxotremorine-M mediated a potent contractile response in urinary bladder from M3 KO mice. This response exhibited an M2 profile in competitive antagonism studies and was completely absent in M2/M3 KO mice. Following 4-DAMP mustard treatment, oxotremorine-M elicited a contractile response in wild-type urinary bladder in the presence of KCl and isoproterenol or forskolin, and this response was diminished in M2 KO mice. Our results show that the M2 receptor mediates contractions indirectly in the urinary bladder by enhancing M3 receptor-mediated contractions and inhibiting relaxation. We also show that it is difficult to detect M2 receptor function in competitive antagonism studies under conditions where a simultaneous activation of M2 and M3 receptors occurs.

Acetylcholine-induced desensitization of the contractile response to histamine in Guinea pig ileum is prevented by either pertussis toxin treatment or by selective inactivation of muscarinic M(3) receptors

We have studied the role of M(2) and M(3) muscarinic receptors in acetylcholine-mediated desensitization of the contractile response to histamine in the guinea pig ileum. Treatment of the isolated ileum with acetylcholine (30 microM) for 20 min caused a marked desensitization of the contractile response to histamine. When measured 5 min after washout of acetylcholine, the EC(50) value of histamine increased 5.8-fold compared with that estimated before acetylcholine treatment, whereas the maximal response was unaffected. This shift in the EC(50) value of histamine was maximal at the earliest time measured after acetylcholine treatment (5 min), and normal sensitivity recovered in approximately 20 min. Acetylcholine-induced desensitization was prevented by uncoupling of M(2) receptors from G(i) with pertussis toxin or by selective inactivation of M(3) receptors with N-2-chloroethyl-4-piperidinyl diphenylacetate (4-DAMP mustard). The shifts in the EC(50) values of histamine measured 5 min after acetylcholine treatment were only 2.0- and 1.8-fold in pertussis toxin- and 4-DAMP mustard-treated ilea, respectively. Both pertussis toxin- and 4-DAMP mustard-treatment had little or no effect on histamine-induced contractions in control ileum. Measurement of histamine-stimulated inositol phosphate accumulation in the longitudinal muscle of the ileum showed little or no inhibitory effect of prior exposure to acetylcholine, indicating that the majority of the heterologous desensitization occurs downstream from phospholipase Cbeta activation. Collectively, our results suggest that activation of both M(2) and M(3) receptors is required for heterologous desensitization of histamine-mediated contractions in the guinea pig ileum.

Functional role of muscarinic M(2) receptors in alpha,beta-methylene ATP induced, neurogenic contractions in guinea-pig ileum

1. The muscarinic acetylcholine receptors mediating the contractile response elicited to endogenous acetylcholine released by the selective P2X receptor agonist alpha,beta-methylene ATP (mATP) were investigated in guinea-pig ileum. 2. mATP (0.1 - 30 microM) elicited a concentration-dependent neurogenic contractile response inhibited by tetrodotoxin (TTX) and antagonized by the non-selective muscarinic receptor antagonist N-methylscopolamine (NMS). 3. The contractile response to mATP was pertussis toxin-insensitive, irreversibly antagonized by N-(2-chloroethyl)-4-piperidinyl diphenylacetate (4-DAMP mustard), and unaffected by the muscarinic M(2)/M(4) receptor selective antagonist AF-DX 116 (1 microM). 4. When measured in the presence of histamine and isoproterenol after treatment with 4-DAMP mustard, mATP elicited a pertussis toxin-sensitive contractile response potently antagonized by AF-DX 116. 5. Collectively, our data suggest that endogenous acetylcholine released by mATP can elicit a direct contractile response through the muscarinic M(3) receptor and an indirect contractile response through the muscarinic M(2) receptor by antagonizing the relaxant effects of isoproterenol on histamine induced contraction.

Muscarinic M3 receptor inactivation reveals a pertussis toxin-sensitive contractile response in the guinea pig colon: evidence for M2/M3 receptor interactions

The role of M2 and M3 receptors in the contractile and phosphoinositide responses elicited to oxotremorine-M was investigated in the guinea pig colon. Under standard conditions, both the contractile and phosphoinositide responses were insensitive to pertussis toxin and irreversibly antagonized by alkylation of M3 receptors with N-(2-chloroethyl)-4-piperidinyl diphenylacetate. After treatment with N-(2-chloroethyl)-4-piperidinyl diphenylacetate, the remaining contractile response was sensitive to pertussis toxin and weakly antagonized by the M2- and M4-selective antagonist AF-DX 116. In contrast, the residual phosphoinositide response was unaffected by pertussis toxin. The pertussis toxin sensitivity of the remaining contractile response suggests that the M2 receptor is mediating the contraction, whereas its weak antagonism by AF-DX 116 suggests that an alternate muscarinic subtype mediates the response. To explain this enigma, we investigated a mathematical model for receptor action based on an interaction between two receptor subtypes (M2 and M3). This model predicts that a response mediated by both the M2 and M3 receptor can be pertussis toxin sensitive yet exhibit an antagonistic profile indicative of an M3 response.

Comparison of functional antagonism between isoproterenol and M2 muscarinic receptors in guinea pig ileum and trachea

The ability of the M2 muscarinic receptor to mediate an inhibition of the relaxant effects of forskolin and isoproterenol was investigated in guinea pig ileum and trachea. In some experiments, trachea was first treated with 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) mustard to inactivate M3 receptors. The contractile response to oxotremorine-M was measured subsequently in the presence of both histamine (10 microM) and isoproterenol (10 nM). Under these conditions, [[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5, 11-dihydro-6H-pyrido[2,3b]-[1,4]benzodiazepine-6-one (AF-DX 116) antagonized the contractile response to oxotremorine-M in a manner consistent with an M3 mechanism. However, when the same experiment was repeated using forskolin (4 microM) instead of isoproterenol, the response to oxotremorine-M exhibited greater potency and was antagonized by AF-DX 116 in a manner consistent with an M2 mechanism. We also measured the effects of pertussis toxin treatment on the ability of isoproterenol to inhibit the contraction elicited by a single concentration of either histamine (0.3 microM) or oxotremorine-M (40 nM) in both the ileum and trachea. Pertussis toxin treatment had no significant effect on the potency of isoproterenol for inhibiting histamine-induced contractions in the ileum and trachea. In contrast, pertussis toxin treatment enhanced the relaxant potency of isoproterenol against oxotremorine-M-induced contractions in the ileum but not in the trachea. Also, pertussis toxin treatment enhanced the relaxant potency of forskolin against oxotremorine-M-induced contractions in the ileum and trachea. We investigated the relaxant potency of isoproterenol when very low, equi-effective (i.e., 20-34% of maximal response) concentrations of either histamine or oxotremorine-M were used to elicit contraction. Under these conditions, isoproterenol exhibited greater relaxant potency against histamine in the ileum but exhibited similar relaxant potencies against histamine and oxotremorine-M in the trachea. Following 4-DAMP mustard treatment, a low concentration of oxotremorine-M (10 nM) had no contractile effect in either the ileum or trachea. Nevertheless, in 4-DAMP mustard-treated tissue, oxotremorine-M (10 nM) reduced the relaxant potency of isoproterenol against histamine-induced contractions in the ileum, but not in the trachea. We conclude that in the trachea the M2 receptor mediates an inhibition of the relaxant effects of forskolin, but not isoproterenol, and the decreased relaxant potency of isoproterenol against contractions elicited by a muscarinic agonist relative to histamine is not due to activation of M2 receptors but rather to the greater contractile stimulus mediated by the M3 receptor compared with the H1 histamine receptor.

Muscarinic M2 receptor-mediated contraction in the guinea pig Taenia caeci: possible involvement of protein kinase C

Contraction of the guinea pig taenia caeci is mediated by muscarinic M3 receptors; however, they comprise only 30% of the muscarinic receptors present. This study investigated the role of the predominant M2 receptor population in contractions and possible second messengers involved after M3 receptors were selectively alkylated by 4-DAMP mustard [N-(2-chloroethyl)-4-piperidinyldiphenylacetate] (60 nM) in the presence of otenzepad (AF-DX 116; 1 microM). Concentration-response curves to oxotremorine-M (oxo-M) in the presence of histamine and isoprenaline were performed in the presence of otenzepad (1 and 3 microM), resulting in a mean apparent pK(B) of 6.49, indicative of an M2 response. As the taenia has intrinsic tone, precontraction with histamine was not necessary and, therefore, in some experiments only isoprenaline was included. In these studies, an M3 response to oxo-M was observed, as the mean apparent pK(B) for otenzepad was 5.89. To investigate protein kinase C (PKC) involvement in the M2 response following M3 inactivation, the inhibitor chelerythrine (1 microM) was included with histamine and isoprenaline in the absence and presence of otenzepad. The oxo-M concentration-response curve was shifted by otenzepad with an apparent pK(B) value of 6.05, a value significantly different from that seen in the absence of chelerythrine (P < 0.05). These results suggest that activation of PKC by a spasmogen such as histamine is necessary to see an M2 response following M3 receptor inactivation.

M2 muscarinic receptors inhibit forskolin- but not isoproterenol-mediated relaxation in bovine tracheal smooth muscle

The ability of the M2 muscarinic receptor to inhibit the relaxant effects of forskolin and isoproterenol was investigated in bovine trachea. In most experiments, we measured contractile responses to oxotremorine-M in smooth muscle isolated from bovine trachea in which a majority of M3 receptors were inactivated by treatment with N-(2-chloroethyl)-4-piperidinyl diphenylacetate. In the presence of histamine (20 microM), the histamine H2 antagonist cimetidine (10 microM) and forskolin (4 microM), responses to oxotremorine-M were antagonized by [[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5, 11-dihydro-6H-pyrido[2,3b][1,4]benzodiazepine-6-one (1 microM) in a manner consistent with contractions mediated predominantly by M2 receptors. When similar experiments were conducted in the presence of isoproterenol (0.1 microM) instead of forskolin, contractions were antagonized in a manner consistent with an M3 receptor-mediated response. In similar experiments, we measured the relaxant potency of isoproterenol and forskolin against histamine-induced contractions in N-(2-chloroethyl)-4-piperidinyl diphenylacetate-treated trachea. By itself, oxotremorine-M (7.5 nM) had no contractile effect; however, it caused a substantial reduction in the relaxant potency of forskolin although having little effect on that of isoproterenol. These experiments establish that M2 receptors inhibit the relaxant effects of forskolin, but not isoproterenol. In untreated tissues, the relaxant responses to isoproterenol and forskolin were 10.8- and 14.2-fold more potent, respectively, against histamine than against oxotremorine-M-induced contractions of equal magnitude. Similarly, the maximal stimulation of cAMP accumulation elicited by isoproterenol and forskolin was inhibited 58 and 62%, respectively, in the presence of oxotremorine-M (80 nM) compared to that measured in the presence of histamine (20 microM). Analysis of the data indicated that isoproterenol elicited relaxation at concentrations well beyond those that stimulated maximal levels of cAMP accumulation. Our results indicate that part of the relaxant response to isoproterenol is mediated through a non-cAMP-dependent mechanism, and that this mechanism is largely unopposed by the M2 receptor.

The use of irreversible ligands to inactivate receptor subtypes: 4-DAMP mustard and muscarinic receptors in smooth muscle

Irreversible ligands are useful tools for investigating the function of receptor subtypes in various physiological processes. The mechanism for alkylation involves the formation of a reversible receptor complex followed by a covalent reaction. The extent of receptor alkylation is determined by the dissociation constant of the reversible complex and the rate constant for conversion to the covalent complex. Selectivity can be achieved if the irreversible ligand exhibits a difference in its dissociation constants for receptor subtypes. Selective alkylation can also be achieved using a selective competitive inhibitor to protect the desired receptor subtype. By using the non-M2-selective irreversible antagonist, 4-DAMP mustard, in combination with the competitive M2-selective antagonist, AF-DX 116, it has been possible to achieve a highly selective inactivation of all non-M2 subtypes of the muscarinic receptors in smooth muscle and has enabled the discovery of the functional role of M2 receptors in smooth muscle.

Effects of antimitotic agents on secretion and detergent extractibility of adrenal nicotinic acetylcholine receptors

1. Evidence exists that associations of adrenal nicotinic acetylcholine receptors (nAChRs) with the cytoskeleton play an important role in signal transduction pathways by maintaining these receptors in a functional state. These studies were designed to explore this possibility and elucidate the mechanism by which antimitotic agents inhibit activation of adrenal nAChRs. 2. Functional studies demonstrated that vincristine, tubulozole, podophyllotoxin, and demecolcine inhibited nAChR-stimulated catecholamine release noncompetitively and in a concentration-dependent manner, with IC50 values of 3 (1-10), 5 (2-10), 8 (4-15), and 19 (9-39) microM, respectively. 3. Detergent extraction experiments indicated that approximately 36% of adrenal nAChRs were associated with the detergent-insoluble cytoskeletal fraction. When chromaffin cells were first treated with antimitotic agents and then detergent solubilized, a significant reduction occurred in the population of adrenal nAChRs associated with the detergent-insoluble cytoskeleton. 4. These studies support an association of adrenal nAChRs with microtubules and suggest that the mechanism by which the antimitotic drugs interfere with the signal transduction pathway is by inducing dissociation of nAChRs from the microtubular network.

Role and mechanisms of action of acetylcholine in the regulation of rat cholangiocyte secretory functions

We investigated, in isolated bile duct units (IBDU) and cholangiocytes isolated from normal rat liver, the occurrence of acetylcholine (ACh) receptors, and the role and mechanisms of ACh in the regulation of the Cl-/HCO3- exchanger activity. The Cl-/HCO3- exchanger activity was evaluated measuring changes in intracellular pH induced by acute Cl- removal/readmission. M3 subtype ACh receptors were detected in IBDU and isolated cholangiocytes by immunofluorescence, immunoelectron microscopy, and reverse transcriptase PCR. M1 subtype ACh receptor mRNA was not detected by reverse transcriptase PCR and M2 subtype was negative by immunofluorescence. ACh (10 microM) showed no effect on the basal activity of the Cl-/HCO3- exchanger. When IBDU were exposed to ACh plus secretin, ACh significantly (P < 0.03) increased the maximal rate of alkalinization after Cl- removal and the maximal rate of recovery after Cl- readmission compared with secretin alone (50 nM), indicating that ACh potentiates the stimulatory effect of secretin on the Cl-/HCO3- exchanger activity. This effect of ACh was blocked by the M3 ACh receptor antagonist, 4-diphenyl-acetoxy-N-(2-chloroethyl)-piperidine (40 nM), by the intracellular Ca2+ chelator, 1,2-bis (2-Aminophenoxy)- ethane-N,N,N', N'-tetraacetic acid acetoxymethylester (50 microM), but not by the protein kinase C antagonist, staurosporine (0.1 microM). Intracellular cAMP levels, in isolated rat cholangiocytes, were unaffected by ACh alone, but were markedly higher after exposure to secretin plus ACh compared with secretin alone (P < 0.01). The ACh-induced potentiation of the secretin effect on both intracellular cAMP levels and the Cl-/HCO3- exchanger activity was individually abolished by two calcineurin inhibitors, FK-506 and cyclosporin A (100 nM).

CONCLUSIONS

M3 ACh receptors are markedly and diffusively represented in rat cholangiocytes. ACh did not influence the basal activity of the Cl-/HCO3- exchanger, but enhanced the stimulation by secretin of this anion exchanger by a Ca2+-dependent, protein kinase C-insensitive pathway that potentiates the secretin stimulation of adenylyl cyclase. Calcineurin most likely mediates the cross-talk between the calcium and adenylyl cyclase pathways. Since secretin targets cholangiocytes during parasympathetic predominance, coordinated regulation of Cl-/HCO3- exchanger by secretin (cAMP) and ACh (Ca2+) could play a major role in the regulation of ductal bicarbonate excretion in bile just when the bicarbonate requirement in the intestine is maximal.

The interaction of 4-DAMP mustard with subtypes of the muscarinic receptor

The compound 4-DAMP mustard (N-2-chloroethyl-4-piperidinyl diphenylacetate) is a 2-chloroethylamine derivative of the selective muscarinic antagonist 4-DAMP (N,N-dimethyl-4-piperidinyl diphenylacetate). At neutral pH, 4-DAMP mustard cyclizes spontaneously into an oziridinium ion that binds covalently with muscarinic receptors. Analysis of the kinetics of receptor alkylation showed that the interaction of 4-DAMP mustard with M2 and M3 receptors was consistent with a model in which the aziridinium ion rapidly forms a reversible complex with the receptor which converts to a covalent complex at a relatively slower rate. The rate constant (k2) for alkylation of M2 and M3 receptors was approximately the same (k2 = 0.1 min-1); however, the affinity of the aziridinium ion for the M3 receptor (KD = 7.2 nM) was approximately 6.3-fold greater than that for the M2 receptor (KD = 43 nM). The results of competitive binding experiments on Chinese hamster ovary cells transfected with the M1 - M5 subtypes of the muscarinic receptor showed that the affinity of the aziridinium ion for the M1, M3, M4 and M5 subtypes was approximately the same and about 11-fold greater than that for the M2 receptor. 4-DAMP mustard is a useful tool for selectively inactivating all non-M2 muscarinic receptors, particularly when it is used in the presence of a reversible M2 selective antagonist to protect the M2 receptor from alkylation. The results of studies on isolated smooth muscle preparations that have had their M3 receptors alkylated with 4-DAMP mustard are consistent with the postulate that the M2 receptor can elicit contraction by inhibiting the relaxant effect of isoproterenol and forskolin on histamine induced contractions.

Selective blockade of M2 and M3 muscarinic receptors by hexahydrobenzyl-fourdapine and a comparison with zamifenacin

1. 4-Diphenylacetoxy-N-cyclohexylmethyl-piperidine HCl (hexahydro-benz-4DAP) is more active as an antagonist of carbachol at receptors in guinea-pig isolated ileum, log K (pA2) = 6.64 +/- 0.14 (s.e. 7 results), than at receptors in guinea-pig isolated atria, log K = 5.43 +/- 0.14 (7). In the presence of neostigmine bromide (0.2 microM) the value for atria was 5.62 +/- 0.19 (4), so the lower activity on atria cannot be attributed to hydrolysis of the compound by cholinesterases present in this tissue. 2. The limit of solubility of the free base in Krebs solution (pH 7.6) is about 50 microM for both hexahydrobenz-4DAP and benzyl-fourdapine (benz-4DAP). 3. In experiments on guinea-pig isolated ileum with hexahydro-benz-4DAP given together with 4-DAMP methobromide, the combined dose-ratio was consistent with competition: similar results were obtained with benz-4DAP. 4. In rats anaesthetized with pentobarbitone, hexahydro-benz-4DAP antagonized the effects of bethanechol on blood-pressure in doses that had little effect on heart rate or airflow. There was a limit to the effect which could be obtained, however, and the slopes of the Schild plots were less than one. The effects on rat blood-pressure had a half-life of at least 30 min. 5. In similar experiments with zamifenacin the slopes of the Schild plots were close to 1 and the compound was 10 to 20 times as active on blood-pressure at it was on heart-rate. 6. The limited solubility of the base probably accounts for the flat Schild plots obtained with hexahydro-benz-4DAP, which had about 10 fold selectivity for effects on blood-pressure and was more active than expected from tests on isolated ileum.

Role of muscarinic M2 and M3 receptors in guinea-pig trachea: effects of receptor alkylation

Muscarinic M2 receptors account for more than half the muscarinic receptor population in smooth muscles of a number of species and yet it is the smaller M3 receptor population that mediates contraction of many of these tissues. The role of the majority of M2 receptors in the control of smooth muscle tone is unclear. In guinea-pig ileal smooth muscle, an indirect contractile role (re-contraction) for M2 receptors has been demonstrated in tissues subjected to M3 receptor alkylation and stimulation of adenylyl cyclase. The present studies have employed the technique of irreversible receptor alkylation in order to investigate the role of muscarinic M2 and M3 receptors in the control of guinea-pig tracheal smooth muscle tone. Experiments were performed to determine (i) whether an indirect contractile role for M2 receptors can be demonstrated in tracheal smooth muscle as described for ileum, and (ii) whether stimulation of M2 receptors can inhibit isoprenaline-induced relaxations of histamine pre-contracted trachea after selective M3 receptor alkylation. Our results suggest (i) that there is no evidence of M2 receptor-mediated re-contraction of tracheal smooth muscle after M3 receptor alkylation and stimulation of adenylyl cyclase, but (ii) that activation of M2 receptors, after M3 receptor alkylation, has a small inhibitory effect on relaxant responses to isoprenaline in guinea-pig tracheal smooth muscle. Therefore, it appears that the major role of postjunctional muscarinic M2 receptors in guinea-pig trachea remains to be determined.

Cardioselective derivatives of 2,2-diphenyl-2-ethylthioacetate do not discriminate between m2 and m3 muscarinic receptors expressed in CHO cells

Characteristics of interaction of two derivatives of 2,2-diphenyl-2-ethylthioacetate with muscarinic receptors were studied in Chinese hamster ovary (CHO) cells stably transfected with the genes of human m2 and m3 muscarinic receptors. Data from radioligand-receptor binding assays and measurements of m2 receptor-inhibited cyclic AMP formation and m3 receptor-stimulated phosphoinositide (PI) hydrolysis showed that this new series of muscarinic receptor antagonists exhibited a middle range of affinities in binding to muscarinic receptors (Ki = 0.2-0.7 mumol/l), without being able to discriminate between m2 and m3 receptors. They completely displaced [3H]N-methylscopolamine ([3H]NMS) binding at equilibrium and inhibited receptor-mediated increase in PI turnover in m3 CHO cells and decrease in cyclic AMP synthesis in m2 CHO cells in an apparent competitive manner. However, higher concentrations of the compounds (> 10 mumol/l) decelerated the kinetics of atropine-induced dissociation of [3H]NMS at m2 and m3 receptors, indicating an allosteric interaction. Collectively, our results demonstrate that these derivatives of 2,2-diphenyl-2-ethylthioacetate display a mixed mechanism of interaction with muscarinic receptors, being competitive at low concentrations and allosteric at higher concentrations. In contrast to previous reports of a significantly higher affinity at cardiac M2 as compared to ileal M3 receptor, these compounds do not exhibit such selectivity when the two receptor subtypes are expressed in the same type of cells.

Dialkylaminoalkyl esters of 2,2-diphenyl-2-alkylthioacetic acids: a new class of potent and functionally selective muscarinic antagonists

The synthesis and pharmacological activity as muscarinic antagonists of a number of 2-alkylthio-2,2-diphenylacetic acid esters are reported. The compounds studied are potent muscarinic antagonists and many of them show from moderate to high selectivity toward M2 or toward M1 and M2 receptors when tested on tissues but lack selectivity on five muscarinic human receptors (m1-m5) cloned and expressed in CHO-K1 cells. As a consequence, the compounds behave as functionally selective antagonists. Those showing M2 selectivity appear to be good drug candidates for the treatment of cognitive disorders connected with central cholinergic deficit.

The effect of muscarinic receptor alkylation on endothelium-dependent vasodilation in SHR

Possible hypertension-related alterations in the nature- and receptor reserve of the muscarinic (M) receptors mediating endothelium-dependent vasodilation remain to be elucidated. Therefore we used 4-diphenylacetoxy-N-(2-chloroethyl)-piperidine (4-DAMPmustard), an irreversible M3-receptor antagonist, to estimate the receptor reserve for the methacholine (MCh)-induced endothelium-dependent vasodilation in perfused mesenteric vascular bed preparations obtained from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) rats, respectively. The concentration-response curve parameters for the MCh-induced vasodilation were similar in both types of preparations. 4-DAMPmustard concentration-dependently decreased the maximal effect (Emax) of MCh without altering (N.S.) the pD2 in either type of preparation. The Emax was decreased to the same extent (N.S.) in both types of preparations. The dissociation constants of MCh for the response to muscarinic stimulation were comparable in preparations from SHR and WKY rats. The receptor reserve for this response, which is relatively low, does not appear to differ between vessels from SHR and WKY. It is concluded that an endothelial dysfunction does not seem to occur in perfused mesenteric resistance vessels from SHR. Also, the nature- and M-receptor reserves to not appear to differ. Therefore there are no important hypertension-related alterations in the M-receptor mediating endothelium-dependent vasodilation, at least in the experimental model used.

[The participation of the cholinergic systems in the bulbar mechanisms regulating breathing]

An unequal distribution of M- and N-cholinergic systems was revealed in symmetrical medullary structures. The data obtained suggest involvement of a cholinergic transmission in the mechanisms of integration of parts of the bulbar respiratory centre for the control of respiration.

Selective inactivation of muscarinic M2 and M3 receptors in guinea-pig ileum and atria in vitro

1. The role of muscarinic M2 and M3 receptors in ileal smooth muscle has been evaluated by use of selective receptor alkylation. The alkylating agents, 4-diphenylacetoxy-N-(2-chloroethyl)-piperidine (4-DAMP mustard) was studied for effects against (+)-cis-dioxolane, at muscarinic M2 and M3 receptors in guinea-pig atria or ileum, respectively. 4-DAMP mustard (10 nM, 40 min exposure) did not discriminate between these muscarinic receptors. In ileum, 4-DAMP mustard, at 100 nM, resulted in a large dextral shift (197 fold) and depression in maxima. In atria there was a smaller dextral shift (14 fold) but no depression in maxima. 2. The muscarinic antagonists, atropine (non-selective), methoctramine (M2-selective) and para-fluorohexahydro-siladiphenidol (pFHHSiD; M3 selective) were studied in protection studies against alkylation by phenoxybenzamine. Washout studies following equilibration of the tissues with atropine (30 nM), methoctramine (0.3 microM) or pFHHSiD (3 microM), showed the compounds to be reversible. No temporal changes in sensitivity to (+)-cis-dioxolane were observed. 3. Exposure, for 20 min, of atria and ileum to phenoxybenzamine (3 and 10 microM respectively) caused dextral shifts and depressions in the maxima of the concentration-response curve to (+)-cis-dioxolane. These effects were inhibited by prior equilibration with atropine (30 nM) and methoctramine (0.1 microM) in atria or atropine (30 nM) and pFHHSiD (3 microM) in ileum. Similar results in ileum were obtained when pilocarpine was used as the agonist. 4. These data were consistent with muscarinic M2 receptors mediating responses in atria and M3 receptors mediating responses in ileum. No evidence was provided for a direct role of muscarinic M2 receptors in ileal contraction.5. It is concluded that receptor protection by reversible antagonists for muscarinic M2 or M3 receptors provides a means to isolate pharmacologically a single subtype in a tissue possessing heterogeneous populations. This technique may prove useful in defining the role of the respective subtypes in smooth muscle contraction.

Functional role for the M2 muscarinic receptor in smooth muscle of guinea pig ileum

A functional role for the M2 muscarinic receptor in smooth muscle contraction was investigated in isolated guinea pig ileum. Contractile responses to the muscarinic agonist oxotremorine-M (oxo-M) were measured in isolated ilea that had been pretreated with histamine (0.32 microM) and isoproterenol (0.64 microM) to achieve conditions of elevated cAMP. The resulting concentration-effect curve was biphasic, consisting of high (0-50 nM) and low (> 50 nM) potency components. The reversible M2-selective antagonist AF-DX 116 ([[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11- dihydro-6H-pyrido[2,3b][1,4]benzodiazepine-6-one) (1 and 10 microM) shifted this curve in a manner that was inconsistent with competitive antagonism at a single receptor site; the high affinity component was significantly blocked, whereas there was little effect on the low affinity portion of the curve. To inactivate the M3 muscarinic receptors selectively, ilea were incubated with the irreversible M1/M3-selective muscarinic antagonist 4-DAMP mustard [N-(2-chloroethyl)-4-piperidinyldiphenylacetate] (40 nM) for 1 hr in the presence of AF-DX 116 (1 microM) and were then washed extensively. Under these conditions, the contractile responses to oxo-M, in the presence of histamine and isoproterenol or forskolin, were antagonized by AF-DX 116 (1 microM) in a manner consistent with that mediated by an M2 receptor. AF-DX 116 caused 6.6- and 11-fold increases in the EC50 value for oxo-M for ilea pretreated with isoproterenol and forskolin, respectively, and a significant increase in the Hill coefficient in both cases. Under basal conditions, AF-DX 116 caused only a 1.34-fold increase in the EC50 value and no change in the Hill coefficient. In addition, under basal conditions 4-DAMP mustard treatment shifted the oxo-M contractile response curve to the right approximately 20-fold. However, when histamine was present in combination with isoproterenol or forskolin 4-DAMP mustard treatment shifted the concentration-effect curves for oxo-M to the right only about 3.5-fold. Oxo-M produced an M3-mediated stimulation of phosphoinositide hydrolysis in the longitudinal muscle of rat ileum with an EC50 value of 30 microM. 4-DAMP mustard (10 nM; 1 hr) prevented this response, resulting in a 6.6-fold increase in the EC50 value with a 65% reduction of the maximal response. In contrast, this treatment blocked M2-mediated inhibition of isoproterenol-stimulated adenylate cyclase with only a 2-fold increase in EC50, without affecting maximum inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of a smooth muscle antagonist on contraction of patched intestinal defects

Growing new intestinal mucosa on serosal patches may potentially increase intestinal surface area but is limited by contraction of the serosal patch. Since this might be related to smooth muscle contraction or altered collagen metabolism, our aim was to determine whether the smooth muscle antagonist thiphenamil inhibits contraction. Fifty rabbits had two 2 x 5-cm full-thickness intestinal defects patched with adjacent cecum. Group I (n = 25) received saline and Group II (n = 25) 0.02 M thiphenamil at 10 cc/hr intraluminally. Animals were sacrificed at 1, 3, 5, 7, and 10 days. Group II had significantly less contraction of the proximal patch until the 10th day after patching (84 +/- 8 vs 66 +/- 20% Day 1, 67 +/- 4 vs 52 +/- 9% Day 5, 42 +/- 14 vs 42 +/- 7% Day 10). Epithelialization of patches was significantly less in Group II animals at 10 days (88 +/- 8 and 86 +/- 11% vs 47 +/- 20 and 50 +/- 16%, P less than 0.05) but crypt cell production rate and villus height were similar. The hydroxyproline content of regenerating tissue increased significantly 7 and 10 days after patching but was similar in the two groups (30.8 +/- 5.9 micrograms/mg tissue Day 10 vs 12.8 +/- 2.8 Day 1). Smooth muscle antagonism by thiphenamil inhibited contraction of serosal patches but had a deleterious effect on epithelialization and mucosal enzyme activity. The transient effect of thiphenamil and the associated increase of hydroxyproline content suggest that collagen may have the predominant role in contraction.

Inactivation of brain cortex muscarinic receptors by 4-diphenylacetoxy-1-(2-chloroethyl) piperidine mustard

We demonstrated in this study that 4-DAMP [4-diphenylacetoxy-1-(2- chloroethyl) piperidine] mustard, which cyclizes to the aziridinium ion, behaved as a non-selective, non-competitive inhibitor of muscarinic receptors in rat brain cortex. It inactivated to the same extent the M1, M2 and M4 muscarinic receptors present in this tissue, as well as receptors accessible or not accessible to quaternary antimuscarinic drugs. Under mild incubation conditions, the muscarinic receptors in a state with super high affinity for agonists (SH receptors) were less affected by preactivated 4-DAMP mustard than the receptors in the states with lower affinity for agonists (H and L receptors).

Rapid evaluation of the efficacy of pharmacologic agents and their analogs in enhancing bladder capacity and reducing the voiding frequency

We report here the results of a simplified screening method to rapidly compare the pharmacologic action of drugs relevant to the urinary tract. This method avoids the use of anesthesia and of external infusion into the bladder relying on the physiological stimulation of the volume-evoked micturition reflex (VEMR) by diuresis. Mature female rats weighing 240-310 g were placed in restrainer cages that afforded access to food and water but limited movement. Under the rear of the rat, a collecting funnel and weight measuring device was secured. For each VEMR, the weight of the volume voided was recorded on a polygraph which also provided a record of the time of voiding. To evaluate the relative pharmacologic efficacy of the drug under study, 1 mg/kg furosemide along with the drug to be evaluated was diluted in 5 ml of saline and injected subcutaneously. Rats received approximately equimolar concentrations of thiphenamil and 15 other analogs, Ca2+ channel blockers, and K+ channel openers. The furosemide was given to obtain a controlled level of diuresis and avoid the effects of circadian variations in urine flow. Parameters considered were 1) mean volume voided per VEMR, 2) frequency, 3) output, and 4) latency. This model allows the rapid evaluation of drugs designed to increase bladder capacity and decrease the frequency of voiding, and it is particularly useful in evaluating the relative efficacy of drugs that are chemical analogs.

Relaxant effect of thiphenamil HCl on upper urinary tract frequency of contraction of healthy asymptomatic volunteers

The pharmacologic effect of thiphenamil HCl on the upper urinary tract as a relaxant of renal pelvic contractions was studied. A total of 17 subjects with no known upper urinary tract abnormalities were scanned. A Diasonics ultrasound scanner at 3.5 MHz was used to visualize the kidney and renal pelvis with the subject in the supine position. Control recordings of renal pelvic and calyceal contractility were made on videotape for approximately 30 min. The subject was then given a single dose of 400 mg thiphenamil HCl and visualization of contractility continued for approximately 60-90 min. Criteria for the evaluation of the data were the mean frequency of pelvic contraction cross-section of the pelvis, and velocity and direction contraction. Ultrasonic images were filtered by a video filtering process and averaged using the digital conversion and summation in real time. The results show that under control conditions renal pelvic contractions are at a frequency of 2 +/- 1.8 min-1. Contractions are initiated with the intrarenal pelvis and continue towards the ureter at a rate of 1.3 +/- 0.8 cm/s. Following thiphenamil HCl, there is a significant reduction in pelvic contraction frequency, 0.6 +/- 0.6 min-1, and the opposing walls of the renal pelvis do not completely close in the formation of a bolus. The results obtained from this study demonstrate that thiphenamil suppresses upper urinary tract contractility. As a consequence of this observation, it is postulated that this agent may be of use in the acute relaxation of the upper urinary tract for renal colic and stone management.

Pharmacologic effect of thiphenamil HCl on lower urinary tract function of healthy asymptomatic volunteers

The effect of thiphenamil HCl on the urodynamic parameters of bladder filling, voiding and isometric contraction was examined in controls. Data were obtained from 25 control female subjects with a mean age of 27.6 +/- 6.6 years. Three urodynamic studies were done on each subject on 3 different days. These studies were: (1) control study, (2) drug study with a single oral dose of 400 mg thiphenamil HCl and (3) another with 800 mg. Each urodynamic study involved filling and voiding cystometrograms to characterize stability, sensations of fullness and urgency, bladder capacity, urethral opening pressure, maximum flow rate, maximum detrusor pressure and residual urine. In addition, isometric detrusor pressure measurements were made at bladder volume increments of 100 ml. Each urodynamic study was done in the sitting position using medium fill water cystometry at 20 ml/min. Isometric pressures were made by catheterizing the subject with an 18-french three-way Foley catheter with a 30-ml balloon. One lumen was used to fill the bladder and the second to measure pressure. The results show that bladder capacity and the volume at which sensations of fullness and urgency are expressed are not significantly changed under the influence of thiphenamil HCl. Significant differences were seen in the maximum pressure generated by the detrusor during voiding and in the maximum urine flow rate. These differences were most pronounced at the 800-mg thiphenamil HCl dose. The isometric data show a highly significant increase in the maximum isometric pressure developed at the low bladder volumes.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacologic treatment of detrusor incontinence with thiphenamil HCl

A controlled double-blind crossover study is reported in which quantitative urodynamic data and qualitative information are combined to evaluate the treatment of detrusor incontinence using thiphenamil HCl in patients with detrusor instability. Patients placed on the treatment protocol were randomized to placebo or thiphenamil 400 mg q.i.d. Two weeks of thiphenamil HCl or placebo administration were followed by 1 week of washout followed by a cross-over to an additional 2 weeks of placebo or thiphenamil HCl administration. Of the 23 patients 7 dropped out at various stages of the study. The mean age of patients studied was 44 +/- 14 years old. Throughout the study, patients were asked to complete a formalized diary card of the amount and time of voiding and the incidence of incontinence. Three urodynamics studies were done in the following sequence: pretreatment, postwashout, and posttreatment. Parameters of bladder capacity, sensations, stability and pressure/flow were obtained. In addition, resting urethral closure pressures were recorded. The results show that the frequency of incontinence, which was based on the patients' responses, decreased significantly (0.01 less than p less than 0.025). There was an insignificant decrease in the number of voidings and increase in the amount voided each time. Patients on thiphenamil reported that their pads were significantly drier from baseline (p = 0.01). In response to questions comparing problems caused by urine loss during baseline and thiphenamil treatment, analysis shows a significant decrease of problems due to loss of urine (p = 0.01) when the patient was taking the drug compared to the placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxation mechanisms of antispasmodics papaverine and thiphenamil on the human corpus cavernosum

The relaxation mechanism of the antispasmodics, papaverine and thiphenamil on isolated human corpus cavernosum (CC) was investigated. CC tissues were obtained from 12 impotent men undergoing surgery for insertion of penile prostheses. CC preparations were mounted in a tissue bath and the isometric tension was recorded. Papaverine and thiphenamil consistently inhibited high-potassium ([K])-induced contractions in a dose-dependent manner. Noradrenaline (NA)-induced contractions were inhibited by both agents in a non-competitive manner. The pD'2 values were 4.77 +/- 0.20 for papaverine and 4.58 +/- 0.13 for thiphenamil. Papaverine at 10(-4) M, the concentration at which high-[K]-induced contraction was abolished, suppressed NA-induced contraction by approximately 85%. In the Ca2(+)-free solution containing two mM EGTA, NA-induced contraction was suppressed by approximately 90%. This contraction was inhibited by papaverine or thiphenamil in a dose-dependent manner and was abolished by papaverine at 10(-4). These results suggest that papaverine and thiphenamil relax CC tissue by the inhibition of extracellular Ca2+ influx (mainly voltage-dependent Ca2+ influx) and by the inhibition of release and/or storage of intracellular stored Ca2+.

[Effect of M and N-cholinoblockers on the excitability of the dorsal hippocampus in acute alcoholic intoxication]

It has been established in chronic experiments on rabbits that acute alcohol intoxication increased the after-discharge thresholds in response to electrical stimulation of dorsal hippocampus. It has been shown that neurotropic agents selectively blocking M- or N-cholinoceptors exerted various effects. M-cholino-blocker methamizol (1 mg/kg, i. p.) decreased the excitability of dorsal hippocampus, potentiated EEG and behavioural effects of alcohol intoxication. N-cholinoblocker etherophen (IEM-506, 20 mg/kg, i. p.), on the contrary, increased the excitability of dorsal hippocampus and reduced behavioural effects of alcohol administration.

Functional and direct binding studies using subtype selective muscarinic receptor antagonists

1. Muscarinic receptor antagonists were examined in direct binding studies on guinea-pig cardiac and cortical muscarinic receptors. Pirenzepine, dicyclomine and hexahydroadiphenine were shown to be selective ligands for the putative M1-muscarinic receptor. 2. Functional affinity estimates of the muscarinic ligands studied was determined from their ability to inhibit carbachol-stimulated inositol phosphate (IP) accumulation in guinea-pig cortical slices. 3. The affinity estimates for the inhibition of muscarinic agonist-stimulated IP accumulation were better correlated with affinity estimates obtained from binding studies on the M1 than the M2 muscarinic receptor. 4. These data provide additional evidence, both from direct binding and functional studies, for the presence of M1 and M2 muscarinic receptor subtypes.

Analysis of the in vitro pharmacologic response of renal pelvis and detrusor smooth muscle to thiphenamil, oxybutynin and verapamil

A new computerized methodology was used to acquire and analyze the relative pharmacologic sensitivity of the renal pelvis and urinary bladder of the rabbit to pharmacologic stimulation. Comparison was made of the effects of thiphenamil, verapamil and oxybutynin on the spontaneous contractions of isolated detrusor and renal pelvis. Data collected by computer were evaluated in terms of amplitude, frequency, and tension change to varying concentration of pharmacologic stimulation. Data were analyzed using a frequency/time domain algorithm developed specifically to evaluate the contribution of the oscillatory components of tension associated with smooth muscle tissues. For the renal pelvis the results show 6 X 10(-5) M thiphenamil, 10(-3) M oxybutynin, and 5 X 10(-6) M verapamil resulted in a 50% inhibition of the phasic contractions. Thiphenamil significantly increased the contractile frequency of the renal pelvis. For the bladder 10(-3) M thiphenamil resulted in a 50% inhibition of the phasic contractions, while 3 X 10(-4) M oxybutynin and 3 X 10(-6) M verapamil were needed to achieve the same level of inhibition. Thiphenamil at lower doses (10(-4) M to 5 X 10(-4) M) showed a biphasic effect--an increase of the bladder tissue activity followed by a relaxation phase--that oxybutynin and verapamil failed to produce. The results show that the calcium blocker suppresses the spontaneous activity of the upper and lower urinary tract at lower concentrations than the anticholinergic or thiphenamil.

[Structure of the pressor reaction to angiotensin]

In anesthetized rats, 1938 blood pressure (BP) responses to i.v. injections of angiotensin II were studied. 6 types and 21 subtypes of responses were distinguished: vasopressor response followed by BP normalizing (type 1; 42%) or by a transitory BP drop (type 2; 7%); BP elevation without its subsequent decrease (type 3; 3%) preliminary sharp increase of BP followed by a "classic" angiotensin pressor effect (type 4; 3%); biphasic response--a depressor response followed by a pressor one (type 5; 27%); depressor response alone (type 6; 18%). Depressor phases were increased by phentolamine and indomethacin, and were inhibited by atropine and spasmolytin. The responses to angiotensin II seem to have a vector character, cholinergic system attenuating this response.

The use of thiphenamil hydrochloride (Trocinate) to control wound contraction after radial keratotomy

We studied the efficacy of a topical smooth muscle antagonist, thiphenamil hydrochloride (Trocinate), in inhibiting wound contraction in ocular tissue. Fifteen New Zealand white rabbits underwent standard eight-incision radial keratotomy (RK), and eyes were randomly assigned to treatment or control groups. As demonstrated by slit lamp corneal photographs and by ocular histology, transient inhibition of wound contraction lasted approximately one week in all treatment eyes. We conclude that thiphenamil has a temporary, but specific, effect in controlling wound contraction after ocular surgery. Smooth muscle antagonists may be useful for managing cicatricial conditions of the eye.

Determinants of pulmonary fibrosis and lipidosis in the silica model

The conditions which might favour development of the fibrotic or the lipid component of the pulmonary reaction to inhaled quartz were examined in rats. Smaller particle size and freedom from surface contamination by amorphous silica or iron oxide, status of the animals whether specific pathogen-free or conventional, and the resistance of cell membranes to damage appeared to bear on fibrogenesis. Increased membrane stability by treatment with polyvinylpyridine-N-oxide abolished not only the fibrosis but also the response of type II cells and hence lipidosis. The rate and intensity of quartz deposition may also affect the response, a low concentration inhaled over a long period favouring nodulation. No other manipulations, environmental or pharmacological, succeeded in inhibiting lipidosis to the benefit of fibrosis. Guinea pigs, however, behaved differently, their reaction being characterized by massive alveolar accumulation of dust-bearing macrophages and type II cell hyperplasia but not by lipidosis. The species variation is unexplained but macrophage predominance may represent a phase that later transforms to lipidosis. The experimental findings may have implications for forms of pneumoconiosis other than silicosis.

[Effect of N- and M-cholinergic-potentiating and cholinergic-blocking agents on the epileptogenesis of a penicillin focus in the dorsal hippocampus]

Chronic experiments on rabbits with penicillin epilepsy have shown that intravenous injections of the ACHE inhibitor galanthamine (1 mg/kg), and N-cholinergic-blockers, ganglerone (3 mg/kg) and eterofen (8 mg/kg), decreased or suppressed completely epileptogenesis manifestations. Combination of galanthamine with one of the N-cholinergic-blockers markedly increased their anticonvulsive actions. On the contrary, combination of galanthamine with the M-cholinergic-blocker metamizil (0.5 mg/kg) enhanced epileptogenesis activity. It is postulated that both M- and N-cholinergic mechanisms take part in the genesis of penicillin epilepsy. The use of N-cholinergic-blockers and their combinations with M-cholinomimetics as anticonvulsants seems expedient.

[Effect of parasympathetic agents on renin secretion in vitro]

A study was made of the effect of the parasympathetic agents on renin secretion by rat kidney sections after blockade of alpha- and beta-adrenoreceptors by obsidan and dihydroergotamine. The substances under study were administered at the concentrations 10(-8), 10(-6) or 10(-4) M. Renin activity was determined by radioimmunoassay. n-Cholinomimetics (nicotine, cytiton) were discovered to have a marked inhibitory action on renin secretion, reducing it to almost zero at a concentration of 10(-4) M. n-Cholinolytics (spasmolytin, benzohexonium) produced a dose-dependent stimulation of renin secretion with a 10-20-fold maximal increase. m-Cholinomimetics (aceclidin, proserin) and quateron provoked a 3-5-fold increase in secretion without a dose-dependent effect, whereas galanthamine exerted a negligible effect. Pilocarpine and m-cholinolytics (platyphylline, atropine) reduced the secretion by 2 times without a dose-dependent effect. It is assumed that the renal cortex contains n-cholinoreactive systems that have a direct or mediated action on renin secretion and m-cholinoreactive systems that modulate the activity of the former systems.

[Determination of retinol in human blood plasma using high pressure liquid chromatography]

A quantitative procedure for estimation of retinol in human blood plasma using high pressure liquid chromatography involved separation of the retinoids on an reversed phase analytical column. C19-retinoid aldehyde was used as an internal standard. The procedure enabled to detect up to 0.015 microgram of retinol/ml of blood plasma and may be used for routine clinical analyses.

[Neuropharmacological analysis of electroacupuncture analgesia]

It was established in experiments on conscious rats using concurrent recording of pain sensitivity and evoked potentials that the leading part in electroacupuncture analgesia is played by endogenous opioid peptides. However, numerous pharmacological substances can alter the level of electroacupuncture analgesis suggesting the participation in its genesis of different mediator cerebral systems. In the animals resistant to acupuncture, administration of morphine did not produce marked analgetic effect.

[Role of cholinergic mechanisms in the regulation of ATPase activity and the intensity of glycolysis in the rat neocortex, hippocampus and brain stem]

It was shown in experiments in rats that the increase in the level of endogenous acetylcholine induced by galanthamine entails a reduction in Na+, K+-ATPase of neocortical, hippocampal and truncus cerebri microsomes, and in the content of lactic acid in the brain structures in question. Blockage of M-cholinoreceptors with metamisyl is accompanied by the decreased activity of Na+, K+-ATPase in the neocortex and by its elevation in the truncus cerebri. At the same time the content of lactic acid in the cortex rises and that in the truncus cerebri diminishes. No substantial changes in both the biochemical indicators were recorded in the hippocamp. Inhibition of the central N-cholinoreceptors with eterofen reduces the glycolysis intensity in the truncus cerebri and hippocamp. Meanwhile Na+, K+-ATPase activity in the brain structures remains unchanged.

Binding of 2,2-diphenylpropylamine at the aldehyde site of bacterial luciferase increases the affinity of the reduced riboflavin 5'-phosphate site

We have found a new class of inhibitors of the bacterial bioluminescence reaction, the N,N-diphenylalkylamines and acids. We have studied the action of one of these compounds 2,2-diphenylpropylamine. The amine was competitive with the long-chain aliphatic aldehyde substrate (Ki congruent to 0.1 mM) but caused an increase in the affinity of the enzyme for reduced riboflavin 5'-phosphate (FMNH2). The inhibitor was attached to Sepharose 6B by a bis(oxirane) spacer, and the interactions of bacterial luciferase with the immobilized ligand were analyzed. The binding of luciferase to the immobilized inhibitor was enhanced by FMNH2 and was decreased by decanal. The results of these studies showed that the 2,2-diphenylpropylamine-luciferase complex has an increased affinity for FMNH2. Likewise, the FMNH2-luciferase complex has an increased affinity for 2,2-diphenylpropylamine. The inhibitor also binds to the enzyme-4a-peroxydihydroflavin complex to block the binding of the aldehyde substrate, while binding of the aldehyde substrate to either the free enzyme or the enzyme-4a-peroxydihydroflavin complex blocks binding of 2,2-diphenylpropylamine.

[Role of M- and N-cholinergic biosystems of the brain in the mechanisms responsible for optokinetic, postoptokinetic, and reversed postoptokinetic nystagmus]

In rabbits, the effects of different inhibitors: of Achesterase--nivalin, of M-cholinergic receptors--metamizyl and N-cholinergic receptor--eterophen on the optokinetic nystagmus (OKN), positive optokinetic afternystagmus (OKAN) and reversed postoptokinetic nystagmus (RPN) revealed that in mechanism of the OKH, OKAN and RPN both colinergic systems took part: N-cholinergic system in the OKH and OKAN and M-cholinergic system in RPN formation.

[Effect of synaptically active substances on the hyperthermic effect of prostaglandin E2 in rats]

It was established in experiments on unanesthetized rats given intraventricular injections of drugs that hyperthermic effect of prostaglandin E2 (PGE2) was markedly weakened by administering clofelin while isoproterenol had no appreciable effect on PGE2 effects were not prevented by noradrenaline, 5-hydroxytryptamine, phenoxybenzamine, propranolol, deseril, nicotine, metamyzyl and IEM-506. Preliminary administration of oxotremorine and hemicholinium-3 averted PGE2 effect. The disorders of the thermo-regulation centers caused by excess PGE2 are likely to be counterbalanced by the central effect of some synaptically active drugs which affect in particular the function of cholinergic synapses and alpha-adrenoreceptors.

[Effect of cholinolytics on the functional lability of the visual analyzer in cats]

The effect of aminoethers of derivates of glycolic acid (glipine and amizil) in doses of 0.1--5 mg/kg and of derivates of acetic acid (diphacyl and thropacin) in doses of 10--40 mg/kg on bioelectrical activity of the retina was studied in experiments on 10 intact cats. To control the effect of cholinolytics, electrodes were chronically implanted in the visual cortex and EEG ws recorded. It was noted that the frequency of white, yellow, green and blue photic stimuli is reproduced on ERG within the range from 1 to 23 c/s both before the administration of cholinolytics and during their action in all of the used doses. Flash rhythm reproduction was not disturbed (in spite of an increase in the waves' amplitudes in the retinal background bioelectrical activity) following administration of cholinolytic substances. All cholinolytics in all of the studied doses caused in the EEG of the visual cortex an increase in waves' amplitude, i. e. a synchronization.