In vitro characterization of a novel TXA2/PGH2 receptor ligand (S-145) in platelets and vascular and airway smooth muscle.
The stereoisomers of S-145, a novel thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor ligand, were compared to TXA2/PGH2 receptor antagonists, SQ29548 and BM13505 in guinea pig platelets, aortas and trachea. Equilibrium binding assays in platelets yielded Kd values (nanomolar) for (+)-S-145 (0.57 +/- 0.04), (-)-S-145 (9.2 +/- 1.3), SQ29548 (11.1 +/- 0.70) and BM13505 (118 +/- 16). In aortas, the corresponding Kb values (nanomolar) were (0.014 +/- 0.002), (1.90 +/- 0.31), (16.8 +/- 3.3) and (142 +/- 29), respectively, whereas in trachea, the Kd values (nanomolar) were (0.019 +/- 0.004), (1.12 +/- 0.18), (1.94 +/- 0.30) and (18.99 +/- 2.59), respectively. S-145 stereoisomers elicited platelet shape change stereoselectively that was characterized by EC50 values 8 to 16-fold higher than the EC50 values for these ligands to block aggregation induced by TXA2/PGH2 mimetic, U44069. S-145 (+)- and (-)-isomers stereoselectively induced transient aortic contraction at concentrations 214,000- and 16,000-fold higher, respectively, than the corresponding Kb values in this tissue. S-145-induced platelet shape change and aortic contraction were inhibitable by low concentrations of SQ29548. We postulate that S-145 may elicit partial agonist activity in platelets and aorta via lower affinity for the active than inactive state of the TXA2/PGH2 receptor in those tissues. S-145 had no agonist activity in isolated trachea possibly indicating different TXA2/PGH2 recognition sites in aorta and trachea or a smaller preligand ratio of active to inactive TXA2/PGH2 receptors in trachea than in aorta.
Dubé
G P
GP
Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, Indiana.
Mais
D E
DE
Jakubowski
J A
JA
Brune
K A
KA
Utterback
B G
BG
True
T A
TA
Rinkema
L E
LE
Kurtz
W L
WL
D000818:Animals; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D004305:Dose-Response Relationship, Drug; D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated; D006168:Guinea Pigs; D006834:Hydrazines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D011982:Receptors, Prostaglandin / Q000187:drug effects*; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013237:Stereoisomerism; D014132:Trachea / Q000187:drug effects* / Q000502:physiology
D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D011450:Prostaglandin Endoperoxides, Synthetic; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; C056566:S 145; C028429:U 44069; C045749:SQ 29548