Increased bleeding tendency and decreased susceptibility to thromboembolism in mice lacking the prostaglandin E receptor subtype EP(3).
BACKGROUND
Among the prostanoids, thromboxane (TX) A(2) is a potent stimulator of platelets, whereas prostaglandin (PG) I(2) inhibits their activation. The roles of PGE(2) in the regulation of platelet function have not been established, however, and the contribution of PGE(2) in hemostasis and thromboembolism is poorly understood. The present study was intended to clarify these roles of PGE(2) by using mice lacking the PGE(2) receptor subtype 3 (EP(3)(-/-) mice).


RESULTS
Expression of mRNAs for EP(3) in murine platelets was confirmed by quantitative reverse transcription-polymerase chain reaction. PGE(2) and AE-248, a selective EP(3) agonist, showed concentration-dependent potentiation of platelet aggregation induced by U46619, a TXA(2) receptor agonist, although PGE(2) alone could not induce aggregation. PGE(2) and AE-248 increased cytosolic calcium ion concentration ([Ca(2+)](i)), and AE-248 inhibited the forskolin-induced increase in cytosolic cAMP concentration ([cAMP](i)), suggesting G(i) coupling of EP(3). The potentiating effects of PGE(2) and AE-248 on platelet aggregation along with their effects on [Ca(2+)](i) and [cAMP](i) were absent in EP(3)(-/-) mice. In vivo, the bleeding time was significantly prolonged in EP(3)(-/-) mice. Moreover, when mice were challenged intravenously with arachidonic acid, mortality and thrombus formation in the lung were significantly reduced in EP(3)(-/-) mice.


CONCLUSIONS
- PGE(2) potentiated platelet aggregation induced by U46619 via EP(3) by increasing [Ca(2+)](i), decreasing [cAMP](i), or both. This potentiating action of PGE(2) via EP(3) is essential in mediating both physiological and pathological effects of PGE(2) in vivo.
Ma
H
H
Department of Pharmacology Asahikawa Medical College, Asahikawa, Japan.
Hara
A
A
Xiao
C Y
CY
Okada
Y
Y
Takahata
O
O
Nakaya
K
K
Sugimoto
Y
Y
Ichikawa
A
A
Narumiya
S
S
Ushikubi
F
F
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D015232:Dinoprostone / Q000031:analogs & derivatives / Q000494:pharmacology; D004198:Disease Susceptibility; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D015870:Gene Expression; D006470:Hemorrhage / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D010974:Platelet Aggregation / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018078:Receptors, Prostaglandin E / Q000819:agonists / Q000235:genetics / Q000502:physiology*; D058308:Receptors, Prostaglandin E, EP3 Subtype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013923:Thromboembolism / Q000235:genetics / Q000517:prevention & control*
C121546:ONO AE 248; C545648:Ptger3 protein, mouse; D012333:RNA, Messenger; D018078:Receptors, Prostaglandin E; D058308:Receptors, Prostaglandin E, EP3 Subtype; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D015232:Dinoprostone