Investigation of the prostacyclin (IP) receptor antagonist RO1138452 on isolated blood vessel and platelet preparations.
OBJECTIVE
The current study examined the utility of the recently described prostacyclin (prostanoid IP) receptor antagonist RO1138452 (2-(4-(4-isopropoxybenzyl)-phenylamino) imidazoline) as a tool for classifying prostanoid receptors.


METHODS
pA(2) values were determined on isolated smooth muscle and platelet preparations.


RESULTS
RO1138452 antagonized relaxation of human pulmonary artery, guinea-pig aorta and rabbit mesenteric artery induced by the selective IP agonist cicaprost. Schild plots had slopes close to unity, generating pA(2) values of 8.20, 8.39 and 8.12 respectively. Non-surmountable antagonism was sometimes found with the higher concentrations of RO1138452, attributable to the EP(3) contractile action of cicaprost. RO1138452 did not block relaxation of guinea-pig trachea induced by the EP(2)-selective agonist butaprost. In contrast, there was a modest inhibition of butaprost-induced relaxation of human pulmonary artery by RO1138452, implying activation of both EP(2) and IP receptors by butaprost. RO1138452 did not affect relaxation induced by PGE(2) (EP(4) agonist) and substance P (NK(1)/endothelium-dependent agonist) in rabbit mesenteric artery. In human and rat platelet-rich plasmas, RO1138452 antagonized cicaprost-induced inhibition of platelet aggregation in a surmountable manner; pA(2) values may have been affected by binding of RO1138452 to plasma protein. RO1138452 did not affect the inhibitory actions of PGD(2) (DP(1) agonist) and NECA (adenosine A(2A) agonist) in human platelets.


CONCLUSIONS
The data indicate that RO1138452 is a potent and selective IP receptor antagonist. RO1138452 represents an important addition to our armoury of prostanoid receptor antagonists and a potential clinical agent in situations where prostacyclin has a pathophysiological function.
Jones
R L
RL
Department of Pharmacology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, Hong Kong SAR, China. robert.l.jones@strath.ac.uk
Wise
H
H
Clark
R
R
Whiting
R L
RL
Bley
K R
KR
D000527:Alprostadil / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001593:Benzyl Compounds / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects*; D015232:Dinoprostone / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D011485:Protein Binding; D011817:Rabbits; D044006:Receptors, Epoprostenol / Q000037:antagonists & inhibitors*; D013373:Substance P / Q000494:pharmacology
C514222:(2-(4-(4-isopropoxybenzyl)-phenylamino) imidazoline); D001593:Benzyl Compounds; D004791:Enzyme Inhibitors; D007093:Imidazoles; D044006:Receptors, Epoprostenol; D013373:Substance P; D000527:Alprostadil; C048491:butaprost; D015232:Dinoprostone; D019331:NG-Nitroarginine Methyl Ester