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H Ladinsky

Publications and source records attributed to H Ladinsky.

At least 37 records · Page 2Linked to original sources
PubMed1992

Characterization of a novel 5-HT4 receptor antagonist of the azabicycloalkyl benzimidazolone class: DAU 6285.

Three chemical classes of serotonin 5-HT4 receptor agonists have been identified so far: 5-substituted indoles (e.g. 5-HT), benzamides (e.g. renzapride) and benzimidazolones (e.g. BIMU 8). In a search for 5-HT4 receptor antagonists, we have discovered that the benzimidazolone derivative DAU 6285 (for structure see text), is 3-5 times more potent than tropisetron in blocking 5-HT, renzapride and BIMU 8 induced stimulation of adenylate cyclase activity in mouse embryo colliculi neurons. Schild plot analysis yielded Ki values of 220, 181 and 255 nmol/l, respectively. In addition, DAU 6285 showed poor activity as a 5-HT3 receptor ligand with respect to tropisetron, as demonstrated by in vitro binding studies (Ki, 322 vs 2.8 nmol/l) and by its antagonistic activity in the Bezold-Jarisch reflex test (ID50, 231 vs 0.5 micrograms/kg, i.v.). No significant binding (Ki greater than 10 mumol/l) of DAU 6285 to serotonergic 5-HT1A, 5-HT1B, 5-HT1C, 5-HT1D, and 5-HT2 receptors as well as to adrenergic alpha 1, alpha 2, dopaminergic D1, D2 or muscarinic M1-M3 receptor subtypes was found. The data indicate that DAU 6285 has a somewhat higher affinity than tropisetron for 5-HT4 receptors, a property confirmed in functional tests, and much lower affinity than tropisetron for 5-HT3 receptors. The compound represents a new interesting tool for investigating the pharmacological and physiological properties of 5-HT4 receptors.

Animals↗
PubMed1991

The orphan receptor cDNA RDC4 encodes a 5-HT1D serotonin receptor.

The cDNA of RDC4, a putative receptor of the G protein-coupled receptor family, has been cloned by PCR methodology. The primary structure of this receptor showed homology with the serotonin 5-HT1A receptor. In this work, RDC4 mRNA has been injected in Y1 adrenal cells and Xenopus oocytes and RDC4 cDNA has been transfected transiently in cos-7 cells. In all these systems serotonin elicited a rise in cyclic AMP levels. Binding studies on membranes of the transfected cos-7 cells using [3H]-LSD showed a pattern of drug affinities consistent with the known properties of a 5-HT1D receptor. RDC4 therefore codes for a 5-HT1D receptor which in the studied systems is positively coupled to adenylate cyclase.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1991

Azabicycloalkyl benzimidazolone derivatives as a novel class of potent agonists at the 5-HT4 receptor positively coupled to adenylate cyclase in brain.

Recent experimental evidence indicates that central 5-HT4 receptors which are positively coupled to adenylate cyclase, are stimulated by a family of 2-methoxy-4-amino-5-chloro substituted benzamide derivatives. These compounds are also potent stimulants of the gastro-intestinal motility. In this study the ability of three azabicycloalkyl benzimidazolone derivatives, BIMU 1, BIMU 8, and DAU 6215 (structural formulas are given in the text), to stimulate cAMP formation in colliculi neurons in primary culture have been tested. Two of the compounds, BIMU 1 and BIMU 8, which show prokinetic activity in various animal models, were also good agonists at the 5-HT4 receptors, whereas DAU 6215, a drug devoid of prokinetic activity, was only a weak, partial agonist at 5-HT4 receptors. The rank order of their potencies as compared with those of 5-HT and cisapride was as follows: BIMU 8 = cisapride greater than 5-HT greater than BIMU 1 greater than DAU 6215. The efficacies of BIMU 8 and cisapride were comparable (133 +/- 9% and 124 +/- 8% of the maximal 5-HT efficacy, respectively), whereas BIMU 1 and DAU 6215 elicited, respectively, only 72 +/- 11% and 16 +/- 4% of the maximal 5-HT effect. The activities of the azabicycloalkyl benzimidazolone derivatives and 5-HT on cAMP formation were not additive and ICS 205-930 antagonized the stimulatory effect of these compounds with low potency (pKi = 6.1-6.4), further strengthening the notion of interaction with 5-HT4 receptors. In addition, cross desensitization between the effects of 5-HT and the azabicycloalkyl benzimidazolones on adenylate cyclase was noted, another argument in favor of an interaction of these drugs on 5-HT4 receptors.

Adenylyl Cyclases↗
PubMed1991

Synthesis and biological evaluation of new muscarinic receptor antagonists bearing cyclic amidines as cationic heads.

Two classes of compounds, bearing a cyclic amidino moiety instead of the tertiary amino group of the classical antimuscarinic drugs like hexahydrodifenidol 3 were synthesized. Affinities (KD) for the three pharmacologically defined M1, M2 and M3 mAChR subtypes were measured in radioligand binding assays and in functional in vitro studies (KB) in guinea pig ileum and left atrium. The results showed that the replacement of the tertiary amino group in structural analogues of 3 with a cyclic amidino moiety afforded potent antimuscarinic compounds. The selectivity shown for smooth muscle preparations suggests their usefulness as antispasmodics.

Amidines↗
PubMed1990

Guanylpirenzepine distinguishes between neuronal ml and m4 muscarinic receptor subtypes.

Guanylpirenzepine, a polar, non-quaternary analog of pirenzepine, exhibited a novel binding behavior in rat brain regions: in competition binding experiments against [3H]pirenzepine labeling the M1 receptor in membranes from cerebral cortex, hippocampus and striatum, the compound, differently from pirenzepine, displayed heterogeneous binding curves. Computer assisted analysis of these curves, evidenced the existence of two populations of binding sites: a large proportion (84-89%) of high affinity receptors (KH = 64-92 nM) and a remainder with very low affinity (KL = 19-28 microM). Like pirenzepine, guanylpirenzepine showed low affinity for the glandular M3 and the cardiac M2 receptors when [3H]N-methylscopolamine was used to label the receptors in membranes from these two tissues; affinity values for guanylpirenzepine were 1336 and 5790 nM respectively, vs 323 and 683 nM for pirenzepine. We conclude that guanylpirenzepine is able to discriminate between m1 and m4 receptor subtypes and may represent a new tool for deeper studies on muscarinic receptors classification.

Animals↗
PubMed1988

Enhancement of opioid cataleptic response by cortical frontal deafferentation or intrastriatal injection of NMDA-receptor antagonists.

The cataleptic activity of morphine and methadone was markedly potentiated in frontally decorticated rats with no apparent changes in the onset or duration of action. Enhancement of the opioid cataleptic response was not due to changes in the availability of the drugs in the brain. The potentiation of methadone-induced catalepsy in decorticated rats was mimicked in naive rats by intrastriatal (i.s.) application of 2-amino-7-phosphonoheptanoic acid (AP7), a potent and selective antagonist of N-methyl-D-aspartate (NMDA) receptors. Therefore, degeneration of glutamatergic synapses following decortication could be responsible for the changes in behavioral effects caused by opioids. The failure of AP7 to elicit an effect after injection into the n. accumbens fits with the possibility of a selective involvement of the striatum in this phenomenon. That the striatum plays a critical role in the expression of opioid-induced catalepsy was substantiated by the findings that: (1) naloxone, an opioid antagonist, injected i.s., prevents the potentiation of catalepsy induced by methadone and morphine in decorticated animals, (2) oxotremorine, a muscarinic agonist, injected i.s., reverses the enhancement of opioid-catalepsy in decorticated rats, (3) earlier studies by others showed that ablation of the striatum had a facilitatory action on opioid-induced catalepsy. In conclusion, evidence is given that the corticostriatal pathway exerts an inhibitory effect upon narcotic-induced cataleptic behavior. The possibility that this effect is mediated through striatonigral GABAergic output is discussed. The data further suggest that the neuronal mechanisms through which the corticostriatal pathway mediates narcotic catalepsy is operative through activation of NMDA receptors within the striatum.

2-Amino-5-phosphonovalerate↗
PubMed1988

Characterization of the muscarinic receptor subtypes in the rat urinary bladder.

We investigated the nature of the muscarinic receptors present in the rat urinary bladder by performing binding studies with various selective (pirenzepine, AF-DX 116, hexahydrosiladifenidol, benzhexol, 4-diphenyl-acetoxy-N-methyl piperidine methiodide, dicyclomine, secoverine) and classical (N-methylscopolamine, atropine) antagonists. Competition experiments were carried out against [3H]N-methyl scopolamine at 30 degrees C in Na+/Mg2+ HEPES buffer; non-specific binding was determined in the presence of 1 microM 3-quinuclidinyl benzilate. Of all the antagonists examined, only AF-DX 116 exhibited a heterogeneous binding profile (nH less than 1). Computer-assisted analysis showed that the data fitted best to a two-binding site model, revealing the existence of high and low affinity receptors. The affinity values of AF-DX 116, determined in binding experiments carried out in heart and gland homogenates, allowed us to classify the rat urinary bladder receptors into cardiac and glandular subtypes. We suggest that the glandular receptor subtype is involved in smooth muscle contraction, since AF-DX 116 was equally potent in inhibiting smooth muscle contraction and the secretion of saliva.

Animals↗
PubMed1988

Characterization of muscarinic receptor subtypes in human tissues.

The affinities of selective, pirenzepine and AF-DX 116, and classical, N-methylscopolamine and atropine, muscarinic cholinergic receptor antagonists were investigated in displacement binding experiments with [3H]Pirenzepine and [3H]N-methylscopolamine in membranes from human autoptic tissues (forebrain, cerebellum, atria, ventricle and submaxillary salivary glands). Affinity estimates of N-methylscopolamine and atropine indicated a non-selective profile. Pirenzepine showed differentiation between the M1 neuronal receptor of the forebrain and the receptors in other tissues while AF-DX 116 clearly discriminated between muscarinic receptors of heart and glands. The results in human tissues confirm the previously described selectivity profiles of pirenzepine and AF-DX 116 in rat tissues. These findings thus reveal the presence also in man of three distinct muscarinic receptor subtypes: the neuronal M1, the cardiac M2 and the glandular M3.

Brain↗
PubMed1988

Pharmacokinetics of mifentidine after single and multiple oral administration to healthy volunteers.

1. The pharmacokinetics of mifentidine, a new long acting histamine H2-receptor antagonist, were studied using two protocols. 2. In one study, on 5 different days six normal male subjects were given 2.5, 5, 10, or 20 mg mifentidine or placebo orally 60 min before starting a 3 h continuous gastric aspiration during which time blood samples were taken for measurement of mifentidine concentration. 3. The area under the curves of mifentidine plasma levels (AUC) vs time for the four doses was linearly related to the dose for each individual subject (r = 0.972, P less than 0.001). After doses of 2.5, 5, 10 and 20 mg, mifentidine reduced hydrogen ion output by respectively 36, 37, 60 and 75% and secretory volume by 1, 17, 40, and 47%. The effects at the two highest doses were statistically significant. AUC was correlated positively with the percentage reduction in hydrogen ion output (r = 0.802, P less than 0.001) and volume (r = 0.834, P less than 0.001) over a 3 h period. 4. In the second study, the pharmacokinetics were evaluated after once-daily treatment for 14 days in seven subjects given 10 mg and in seven others subjects given 20 mg. 5. After multiple dosing, renal clearance was similar for the two doses (11.6 +/- 2.11 l h-1 for the low dose and 17.0 +/- 2.0 l h-1 for the high dose). Plasma half-life (t1/2 lambda 2) was 16.0 +/- 3.0 h after the 10 mg dose and 11.9 +/- 1.2 h after 20 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1988

Serotonergic control of phenylephrine-induced cyclic 3,5'-adenosine monophosphate and inositol phosphates formation in rat hippocampus.

Chemical lesion of serotonergic afferents to the hippocampus resulted in a potentiation of phenylephrine (PHE) stimulation of cyclic AMP (cAMP) formation in rat hippocampal slices. The concentration-response curve of the alpha-1-agonist in lesioned rats was shifted markedly to the left with the peak increase occurring at a concentration 200 times lower (500 nM) than that required to raise cAMP to the same extent in slices of the sham-operated controls. Adenylate cyclase activity measured on crude homogenate preparations was increased by the lesion, too. The alpha-1 antagonist WB-4101 (dimethyloxyphenoxy-ethylamino-methyl benzo-1,4-dioxan) was the most potent inhibitor of PHE in lesioned rats with an IC50 of 125 nM, 110 times lower than that of prazosin (14 microM); yohimbine and propranolol, respectively, alpha-2 and beta-antagonists caused inhibition only at very high concentrations. Serotonin (10 microM) induced a marked rightward shift in the concentration response of PHE in lesioned rats, without any effect of its own on the cAMP level. PHE stimulated inositol phosphates accumulation in hippocampal slices in a concentration-dependent manner with an EC50 of 20 microM. Chemical lesion of the serotonergic median raphe nuclei caused a significant reduction of PHEs maximal effect on inositol phosphate accumulation by 50% with no change detectable in the EC50. The results imply that both second messenger responses to PHE stimulation are modulated by serotonin. Whether cAMP and phosphatidylinositol-4,5-bisphosphate generated second messengers act in a cooperative manner, or independently, is discussed.

5,7-Dihydroxytryptamine↗
PubMed1988

Binding and functional characterization of the cardioselective muscarinic antagonist methoctramine.

The antimuscarinic properties of the newly synthetized polymethylene tetramine derivative, methoctramine, were investigated in binding and functional assays. Methoctramine displaced the specific binding of [3H]-N-methylscopolamine [( 3H]NMS) and [3H] pirenzepine from membranes of rat tissues with the following order of affinities: heart = cerebellum greater than cortex greater than submandibular glands, the ratio of the affinities of the compound for the heart and the glands amounting to about 130. Computer fits of binding curves generated in cardiac and cortical membranes were compatible with an interaction at one binding site, whereas those in submandibular glands and cerebellum had slopes significantly lower than 1. Experiments performed in cardiac membranes to investigate the effect of methoctramine on the dissociation kinetics of [3H]-NMS showed that concentrations of compound up to 1 microM did not affect the dissociation of [3H]-NMS elicited by an excess of NMS. At greater concentrations (10-100 microM), methoctramine dose dependently inhibited [3H]-NMS dissociation, thus revealing an allosteric interaction. In in vitro functional assays, methoctramine displayed more than 100 times greater affinity for the muscarinic receptors mediating negative inotropic and chronotropic effects in guinea pig atria than for those responsible for tracheal contraction. Similarly, the compound was a more potent antagonist of the bradycardial response to bethanechol than of the bladder tonus increase, saliva secretion and hypotension induced by the muscarinic agonist in anesthetized cats. Finally, in the pithed rat, methoctramine preferentially inhibited cardiac M2 (vagal bradycardia) over ganglionic M1 (McN-A-343-induced hypertension) responses. The evidence appears to characterize methoctramine as being the most selective M2 muscarinic antagonist described to date.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Characterization of muscarinic receptors in guinea pig ileum longitudinal smooth muscle.

Heterogeneity in the muscarinic receptor population of guinea pig ileum longitudinal smooth muscle was found in competition binding experiments against N-methyl[3H]scopolamine using either a cardioselective (AF-DX 116) or a smooth muscle-selective (hexahydrosiladifenidol) antimuscarinic compound. AF-DX 116 recognized 65% of the total receptors with high affinity and 35% with low affinity. Hexahydrosiladifenidol distinguished 24% of the total receptors with high affinity and 76% with low affinity. The two affinity binding constants displayed in smooth muscle by the compounds were similar to those of heart and glands, suggesting that the muscarinic receptor population in the smooth muscle is formed of about 30% glandular type and 70% cardiac type of the M2 receptors. In dissociation experiments, the rate of breakdown of the N-methyl[3H]scopolamine receptor complex in the smooth muscle was rapid and similar to the dissociation of N-methyl[3H]scopolamine from muscarinic receptors in cardiac membranes, supporting the evidence for the presence of a large fraction of the cardiac receptor type in smooth muscle. To further characterize the population of the smooth muscle receptors recognized as glandular type, we performed protection experiments with hexahydrosiladifenidol, which binds to glandular M3 receptors with high affinity. Smooth muscle membranes were initially incubated with this compound and then phenoxybenzamine was added to irreversibly alkylate the remaining unprotected receptors. Data from competition and dissociation binding experiments showed that, under these conditions, this protected fraction of the total receptor population in ileum smooth muscle had all the characteristics of the glandular type, i.e., slow N-methyl[3H]scopolamine dissociation and affinity constants for a series of selective and nonselective muscarinic antagonists in the same order of magnitude as those found in the glandular tissue. These findings, together with the known observation that hexahydrosiladifenidol is more potent in inhibiting the functional activation of muscarinic receptors in smooth muscle relative to heart, lead to the hypothesis that smooth muscle contractility is mediated by a muscarinic receptor subtype similar to that found in glandular tissue.

Animals↗
PubMed1987

Striatal cholinergic function reflects differences in D-2 dopaminergic receptor activation.

The ergot derivatives, bromocriptine, lisuride and quinpirole (Ly-171555), activators of D-2 receptors, increased striatal acetylcholine (ACh) content by about 40% and induced a 30% inhibition of ACh evoked release from striatal slices, similar to the effects of the dopaminergic agonist apomorphine. These actions were a consequence of dopaminergic activation since they were antagonized by pretreatment with the neuroleptic agent, pimozide. In contrast, pretreatment with L-sulpiride (100 mg/kg), a specific antagonist for the D-2 dopaminergic receptor only, prevented the rise of ACh levels induced by apomorphine or quinpirole but did not interfere with the lisuride- or bromocriptine- induced ACh increases. Similarly, inhibition of the ACh evoked release produced by lisuride (3 microM) was prevented by pimozide (1 mg/kg) but not by pretreatment with L-sulpiride. Addition of L-sulpiride (5 microM) to the Krebs solution had no effect on the inhibition of ACh-evoked release induced by lisuride, but a lower concentration (1 microM) antagonized the inhibition induced by quinpirole. Lisuride and bromocriptine responses were both insensitive to sulpiride. These results are discussed in terms of different interaction with the dopaminergic D-2 receptors by the drugs studied.

Acetylcholine↗
PubMed1987

Muscarinic receptor heterogeneity in guinea pig intestinal smooth muscle: binding studies with AF-DX 116.

Muscarinic receptor subtypes in longitudinal and circular smooth muscles of the guinea pig ileum were characterized with the use of the cardioselective antagonist AF-DX 116 in binding competition experiments against 0.3 nM [3H] N-methylscopolamine [( 3H]NMS). This compound recognized a heterogeneous receptor population in both smooth muscles, revealing the existence of different percentages of the cardiac (KD = 92-110 nM) and the glandular (KD = 1150-2541 nM) muscarinic receptor subtypes. These results, together with the low potency displayed by AF-DX 116 to inhibit the agonist-stimulated smooth muscle contraction and salivary secretion allow the suggestion that the glandular muscarinic receptor subtype, showing a low affinity for AF-DX 116, is involved in smooth muscle contraction.

Animals↗
PubMed1987

Characterization of the muscarinic receptor subtype in isolated gastric fundic cells of the rabbit.

The characteristics of the muscarinic receptor in isolated gastric fundic cells from rabbit were determined by radioligand binding techniques and functional tests. The dissociation constants (KDS) of selective (hexahydrosiladifenidol and pirenzepine) and non-selective (N-methylscopolamine and atropine) muscarinic receptor antagonists obtained in competition experiments vs [3H]-N-methylscopolamine were compared with the pA2 values of the drugs as inhibitors of carbachol-stimulated [14C]-aminopyrine accumulation (an index of acid secretion) in the gastric fundic cells. Good correlations were found between the ability of the drugs to inhibit acid secretion and their affinity for muscarinic receptors in the gastric fundic cells. The rank order of potency in both tests was N-methylscopolamine greater than atropine greater than hexahydrosiladifenidol greater than pirenzepine. The character of the muscarinic receptor subtype present on gastric fundic cells was established by comparing the affinity values of the compounds for this receptor with those for the receptors in other rabbit tissues. It was found that only pirenzepine and hexahydrosiladifenidol displayed tissue selectivity in their binding profiles. The KDS for pirenzepine were 13nM for the M1 receptor of the cerebral cortex and about 500 nM for the M2 receptors of the submandibular and gastric glands and heart. Differently from pirenzepine, hexahydrosiladifenidol showed about 10-fold discrimination between the M2 subtype of the gland (KD = 31 nM) and the M2 subtype of the heart (KD = 330 nM).

Aminopyrine↗