Pharmacological characterisation of the enantiomers of BM-5, a muscarinic partial agonist with opposed enantioselectivity between affinity and efficacy.
The interaction of (R) and (S) enantiomers of the chiral oxotremorine analogue BM-5 with muscarinic acetylcholine receptors was studied in vitro using radioligand binding and isolated tissue preparations. The in vivo effects of (R)-BM-5 were also studied in anaesthetised cat. No receptor or tissue selectivity was found for either enantiomer in radioligand binding studies in cells expressing human muscarinic receptors (M1-M5) or in guinea pig tissues. The affinity of (R)-BM-5 was about 40 times, or 15-60 times higher than that of (S)-BM-5 in recombinant cells or in guinea pig tissues, respectively. Both enantiomers induced contraction of the guinea pig isolated urinary bladder and ileum. (R)-BM-5 was more potent than (S)-BM-5 in bladder (EC50 590 and 3500 nM, respectively) and in ileum (EC50 39 and 2600 nM, respectively). The maximal agonist effect was lower for (R)-BM-5 than for (S)-BM-5 in bladder (2.7% and 6.6%, respectively) and in ileum (32% and 48%, respectively). Contractions were completely inhibited by atropine (1 microM). In vivo, (R)-BM-5 induced bladder contraction and salivation after intravenous administration in the anaesthetised cat (ED50 4.1 and 6.2 microg kg(-1), respectively). In conclusion, (R)- and (S)-BM-5 act as partial muscarinic agonists in the isolated bladder and ileum. (R)-BM-5 was the more potent enantiomer but had a lower maximal agonist effect giving an opposed enantioselectivity for affinity and efficacy. (R)-BM-5 showed agonist activity in vivo, confirming in vitro findings. From affinity and efficacy data it can be concluded that the effects of racemic BM-5 are mediated by the (R)-enantiomer.
Sundquist
S
S
Department of Pharmacology, Pharmacia & Upjohn AB, Uppsala, Sweden. staffan.sundquist@eu.pnu.com
Modiri
A R
AR
Nilsson
B M
BM
Hacksell
U
U
Gillberg
P G
PG
Nilvebrant
L
L
D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D002415:Cats; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006801:Humans; D007082:Ileum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D018721:Muscarinic Agonists / Q000378:metabolism / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D010277:Parasympathomimetics / Q000378:metabolism / Q000494:pharmacology; D011759:Pyrrolidines / Q000378:metabolism / Q000494:pharmacology*; D011813:Quinuclidinyl Benzilate / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D011869:Radioligand Assay; D011976:Receptors, Muscarinic / Q000145:classification / Q000378:metabolism; D013237:Stereoisomerism; D014316:Tritium; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism / Q000502:physiology
D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010277:Parasympathomimetics; D011759:Pyrrolidines; D011976:Receptors, Muscarinic; D014316:Tritium; D011813:Quinuclidinyl Benzilate; C038672:N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide