Commercial dry extract of Hedera helix L. is used for the treatment of disorders of the respiratory tract; it is standardized towards papaverine (papaverine equivalent value, PE, activity of 1 g test substance equivalent to the activity of x mg papaverine) by in vitro antispasmodic activity on isolated guinea-pig ileum with acetylcholine as spasmogen. In order to determine the phytochemical basis for the antispasmodic activity, bioassay guided fractionation and subsequent isolation of phenolic compounds (flavonols, caffeoylquinic acids) and saponins (hederacoside C, alpha-hederin, hederagenin) was carried out. Fractions and isolates obtained were investigated for antispasmodic activity and their contribution to the activity of the extract was calculated. Significant activity was found for both saponins and phenolic compounds, the PE values being approx. 55 and 49 for alpha-hederin and hederagenin, 54 and 143 for quercetin and kaempferol, and 22 for 3,5-dicaffeoylquinic acid, respectively. In view of their relative high concentration the saponins contribute most to the anti-spasmodic activity, followed by dicaffeoylquinic acids and the flavonol derivatives. The results indicate that the summed PE value of the compounds mentioned is an acceptable agreement with the PE value of the whole extract determined biologically.

The aim of the present study was to characterize the muscarinic receptor subtype mediating nonadrenergic noncholinergic (NANC) relaxations in the rabbit anococcygeus muscle (RAM) by the use of muscarinic receptor agonists and a battery of key muscarinic antagonists. In addition, experiments were carried out to identify the NANC neurotransmitter(s) involved in the inhibitory NANC neurotransmission. In preparations with histamine-raised tone, the nonselective muscarinic agonists (pD2 values) (+)-muscarine (5.23), cis-dioxolane (5.16), oxotremorine M (4.95) and carbachol (4.06) produced concentration-dependent relaxations corresponding to 72.6-85.0% of the histamine-induced precontraction. In contrast, the subtype-preferring (M1/M4 over M2 and M3 receptors) agonists 4-(3-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343), (S)-4-(dimethylamino)-1-methyl-2-butynyl-N-(3-chlorophenyl)carbamate methobromide [(S)-BN 228], (R)- and (S)-N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide [(R)- and (S)-BM 5] showed no or rather low [(S)-BN 228] muscarinic activity. The low potencies, together with the ineffectiveness of some agonists, indicated a low effective receptor reserve associated with the relaxant response. No contractile responses to (+)-muscarine were observed neither in unstimulated nor in precontracted preparations suggesting that the existence of an excitatory postjunctional muscarinic receptor may be excluded. The nicotinic antagonist hexamethonium had no influence on relaxant responses to (+)-muscarine, but abolished relaxations elicited by (-)-nicotine. This demonstrates that the RAM contains also nicotinic acetylcholine receptors (AchRs) mediating inhibitory NANC responses. Relaxations induced by the stimulation of muscarinic and nicotinic AchRs as well as by electrical field stimulation (EFS) were completely abolished by tetrodotoxin and were also sensitive to the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (L-NOARG), indicating that NO plays an important role as an inhibitory NANC transmitter in RAM. All muscarinic antagonists investigated did not influence the histamine-induced precontraction, but shifted the concentration-response curve of (+)-muscarine to the right in a parallel fashion. Schild analysis yielded regression lines of unit slope, indicating competitive antagonism. The following rank order of antagonist potencies (pA2 values) was found: 11-([4-[4-(diethylamino)-butyl]-1-piperidinyl]-acetyl-5,11-dihydro-6H-py rido (2,3-b) (1,4)-benzodiazepine-6-one hydrochloride (AQ-RA 741; 8.08) = himbacine (8.03) > or = tripitramine (7.69) > or = p-fluorohexahydro-sila-difenidol (p-F-HHSiD; 7.48) > or = methoctramine (7.30) > or = pirenzepine (7.18) > or = guanylpirenzepine (6.24). A comparison of the pA2 values determined in the RAM with published data from binding studies at muscarinic M1-M4 and m5 receptors suggests that the functional muscarinic receptor mediating NANC relaxation in the RAM is of the M4 subtype. Taken together, the results obtained in the present...

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Starting from trichloro(vinyl)silane (0 3 SiCH=CH 2 ), the musearlnie antagonists sila-biperiden and endosila-biperiden [rac-(SiRS,C2SR)-endo-2] were prepared by a seven-step synthesis. Both silanols are configurationally stableininert organic solvents but undergo slow epimerization in aqueous solution (pH 7.4, 32°C) by inversion of the configuration at the silicon atom. The relative configurations of sila-biperiden and endo-sila-biperiden were detennined by single-crystal X-ray diffraction. Both compounds form intennolecular 0-H · · · N hydrogen bonds in the crystal leading to the fonnation of centrosymmetric dimers (sila-biperiden) and infinite chains (endo-sila-biperiden), respectively. Sila-biperiden is a silicon analogue (C/Si exchange) of the antiparkinsonian drug biperiden . In functional phannacological experiments, as weil as in radioligand competition studies, biperiden, sila-biperiden and endo-sila-biperiden behaved as simple competitive antagonists at muscarinic Ml-, M2-, M3-and M4-receptors. The three compounds displayed thc highest affinity for Ml-receptors (pA 2 values: 8.72-8.80; pKi values: 8.8-9.1), intermediate affinity for M4-and M3-receptors, and lowest affinity for M2-receptors (pA 2 values: 7.57-7.79; pKi values: 7.7-7.8). The affi.nity profile (Ml >. M4 > M3 > M2) of biperiden, sila-biperiden and endo-sila-biperiden is qualitatively similar to that of the M1-selective muscarinic antagonist pirenzepine. The antimuscarinic properlies of the C/Si analogues biperiden and sila-biperiden are almost identical. ZusammenfassungDie Antimuscarinica Sila-biperiden C2SR) (CRS,. Sowohl in funktionellen pharmakologischen Untersuchungen als auch in Radioligand-Kompetitionsexperimenten erwiesen sich Biperiden, Sila-biperiden und endo-Sila-biperiden als rein kompetitive Antagonisten an muscarinischen Ml-, M2-, M3-und M4-Rezeptoren. Alle drei Verbindungen zeigten die höchste Affinität zu den Mt-Rezeptoren (pA 2 -Werte: 8.72-8.80; pKrWerte: 8.8-9.1), eine deutlich geringere Affinität zu den M4-und M3-Rezeptoren und die niedrigste Affinität zu den kardialen M2-Rezeptoren (pArWerte: 7.57-7.79; pKi-Werte: 7.7-7.8). Das Affinitätsprofil (Ml > M4 > M3 > M2) von Biperiden, Sila-biperiden und endo-Sila-biperiden ist dem des Mt-selektiven Antimuscarinicums Pirenzepin qualitativ sehr ähnlich. Die antimuscarinischen Eigenschaften der CjSi-Analoga Biperiden und Sila-biperiden sind nahezu identisch.