Superiority of plasma 11-dehydro-TXB2 to TXB2 as an index of in vivo TX formation in rabbits after dosing of CS-518, a TX synthase inhibitor.
We compared plasma 11-dhTXB2 and TXB2 for their ability to reflect in vivo TX formation in rabbits treated with AA and CS-518, a TX synthase inhibitor. The average plasma level of TXB2 in rabbits was much higher than that of 11-dhTXB2, probably because of artificial formation of TXB2 during blood sampling. CS-518 (1 mg/kg, p.o.) caused a long-lasting suppression of the 11-dhTXB2 level, and its inhibitory effect on 11-dhTXB2 was much more extensive than that on TXB2. AA-infusion for 5 min resulted in transient and remarkable increases of both TXs, and prevention of such increases by CS-518 pretreatment (1 mg/kg, i.v.) was shown: inhibitions of 11-dhTXB2 and TXB2 were 85% and 40%, respectively. The inhibitory effect caused by CS-518, which was more clearly observed on plasma 11-dhTXB2 than on TXB2, was due to not only the completely inhibited levels without artificial formation but also the durable high levels based on the long half-life of 11-dhTXB2 in AA-infused rabbits. CS-518 injection during sustained AA-infusion also resulted in a 2-fold faster disappearance of plasma 11-dhTXB2 than was seen without CS-518, despite its long half-life. Considering the absence of artificial formation, the long half-life, and the good response to change of TX formation, plasma 11-dhTXB2 is superior to TXB2 as an index for monitoring in vivo TX synthase activity and its pharmacological modification with AA and CS-518.
Takasaki
W
W
Analytical and Metabolic Research Laboratories, Sankyo Co., Ltd., Tokyo, Japan.
Nakagawa
A
A
Asai
F
F
Ushiyama
S
S
Sugidachi
A
A
Matsuda
K
K
Oshima
T
T
Tanaka
Y
Y
D000818:Animals; D016718:Arachidonic Acid / Q000008:administration & dosage; D015777:Eicosanoids / Q000097:blood; D007124:Immunoenzyme Techniques; D007262:Infusions, Intravenous; D008297:Male; D011817:Rabbits; D011863:Radioimmunoassay; D013876:Thiophenes / Q000494:pharmacology*; D013929:Thromboxane B2 / Q000031:analogs & derivatives* / Q000097:blood*; D013930:Thromboxane-A Synthase / Q000037:antagonists & inhibitors*; D013931:Thromboxanes / Q000096:biosynthesis*
D015777:Eicosanoids; D013876:Thiophenes; D013931:Thromboxanes; C055806:RS 5186; D016718:Arachidonic Acid; D013929:Thromboxane B2; C049235:11-dehydro-thromboxane B2; D013930:Thromboxane-A Synthase