Masatomi Harada

Pharmacological studies on novel muscarinic agonists, 1-oxa-8-azaspiro[4.5]decane derivatives, YM796 and YM954.

We have investigated the pharmacological profiles of the novel muscarinic agonists, 1-oxa-8-azaspiro[4.5]decane derivatives, YM796 (2,8-dimethyl-3-methylene) and YM954 (2-ethyl-8-methyl-3-oxo). These compounds, like the putative M1 agonists, RS86 and AF102B, inhibited [3H]pirenzepine binding to cerebral cortical membranes in the micromolar range and weakly inhibited [3H]quinuclidinyl benzylate binding to cerebellar membranes. Their (-) isomers had Hill coefficients lower than 1.0. (+/-)-YM796, (+/-)-YM954 and RS86, but not AF102B, stimulated phosphoinositide hydrolysis in hippocampal slices, an effect which is mainly linked to M1 receptors. (+/-)-YM796 (0.031 mg/kg p.o.) and (+/-)-YM954 (0.016 mg/kg p.o.) reversed the cognitive impairment in nucleus basalis magnocellularis-lesioned rats in a passive avoidance task more effectively than did RS86 and AF102B. Similar results were obtained in scopolamine-treated rats. Finally, (+/-)-YM796 was weaker than (+/-)-YM954 and RS86 in the induction of tremor, hypothermia and contraction of isolated ileum, which are mainly mediated by M2 and/or M3 receptors. These results suggest that (+/-)-YM796, (+/-)-YM954 and RS86 have M1 agonistic activity in central nervous system and that (+/-)-YM796 has relatively weak M2 and/or M3 agonistic activity.

Effect of a new potent H2-receptor antagonist 3[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]-N2-sulfamoylpropionamidine (YM-11170) on gastric mucosal histamine-sensitive adenylate cyclase from guinea pig

The effect of 3[[[2-[(diaminomethylene)amino]-4- thiazolyl]methyl]thio]-N2-sulfamoylpropionamidine (YM-11170), a new thiazole H2-receptor antagonist bearing propionamidine at the terminus of a side chain, on histamine-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] of gastric mucosa from the guinea pig was studied and compared with that of cimetidine. YM-11170 displaced the concentration-stimulation curve of histamine-sensitive adenylate cyclase to the right with a pA2 of 7.65 (Ki = 2.25 X 10(-8) M). Stimulation of gastric adenylate cyclase by 0.1 mM histamine was competitively inhibited by YM-11170 and cimetidine in a dose-dependent manner, with IC50 values of 5.9 X 10(-7) M and 1.4 X 10(-5) M respectively. Hippocampal histamine-sensitive adenylate cyclase in the presence of 0.1 mM histamine was also competitively inhibited by YM-11170 with an IC50 of 1.1 X 10(-7) M. YM-11170 did not affect Gpp(NH)p-, NaF-, PGE2-stimulated or basal activity of the gastric adenylate cyclase. These data, together with other results, indicate that YM-11170 is a highly selective and potent H2-receptor antagonist which competes with histamine at the receptor site on the histamine-sensitive adenylate cyclase.

Biochemical characteristics of a potential antidepressant, 2-(7-indenyloxymethyl)morpholine hydrochloride (YM-08054-1)

Abstract The effects of potential antidepressant, 2-(7-indenyloxymethyl)morpholine hydrochloride (YM-08054-1), on uptake, release and oxidative deamination of catecholamines and serotonin [5-hydroxytryptamine(5-HT)] were studied in vitro with rat brain, and compared with the effects of several tricyclic antidepressants and viloxazine a structural analogue of YM-08054-1. YM-08054-1 at concentrations of less than 1 μM. considerably inhibited 5-HT uptake by synaptosomes from rat whole brain as well as noradrenaline (NA) uptake by synaptosomes from rat hippocampus, similar to amitriptyline. Viloxazine and iprindole were weak inhibitors in both uptake reactions. In the release of either [14C] -5-HT from [14C]-5-HT-prelabeled hypothalamic slices or [14C]NA from [14C] NA-prelabeled hippocampal slices, YM-08054-1 and amitriptyline were much less potent than such typical potent releasers as methamphetamine and tyramine. YM-08054-1 was also found to be a weak inhibitor of both type A and type B monoamine oxidases, whereas the tricyclic antidepressants preferentially inhibited the type B enzyme. These biochemical results indicate that YM-08054-1 may be an amitriptyline-like antidepressant, but distinct from viloxazine.

Effect of guanine nucleotides on histamine-sensitive adenylate cyclase from the parietal cells of guinea pig

Abstract Histamine-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1.] of gastric parietal cell membranes from the guinea pig was at least 10-fold stimulated by histamine ( K a = 0.60 μ M) in the presence of 2 m m MgCl 2 and further potentiated by about 1.5-fold by the addition of 10 μ m GTP ( K a = 0.34 μ M). 5′-Guanylylimidodiphosphate (Gpp(NH)p), on the contrary, reduced markedly the histamine sensitivity with the K i of 0.038 μ m and this inhibition was abolished by the addition of GTP. Under the assay conditions using 1 m m 5′-adenylylimidodiphosphate (App(NH)p) as substrate in the presence of 2 m m MgCl 2 , adenylate cyclase was only 3-fold stimulated by histamine with the K a of 0.76 μ m . This histamine sensitivity was not affected by as much as 0.1 m m Gpp(NH)p while reduced markedly at the concentration of 1 m m without altering the basal activity. Half-maximal activation of the histamine-sensitive activity by GTP in the presence of App(NH)p as substrate occurred at 2.3 μ m , and GDP was as effective as GTP in the potentiation. Under the assay conditions in the presence of 21 m m MgCl 2 and ATP as substrate, 1 μ m Gpp(NH)p alone elevated the basal activity to the maximally histamine-stimulated level and this stimulation was almost entirely abolished by the addition of 10 μ m GTP. These results suggest that, in contrast to the general concept in the action of guanine nucleotides on other hormone-sensitive adenylate cyclases, GTP and Gpp(NH)p compete for a regulatory nucleotide binding site of histamine-sensitive adenylate cyclase from the gastric parietal cells with functionally reciprocal effects possibly through different conformational changes of the nucleotide binding protein.