A thromboxane A (2) system in the Atlantic stingray, Dasyatis sabina

Cabrera, D.M.; Janech, M.G.; Morinelli, T.A.; Miller, D.H.

General and Comparative Endocrinology 130(2): 157-164

2003


ISSN/ISBN: 0016-6480
PMID: 12568793
DOI: 10.1016/s0016-6480(02)00586-5
Accession: 010104926

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Abstract
Thromboxane B2 (TXB2) is the stable metabolite of thromboxane A2 (TXA2) and thromboxane B2-like immunoreactivity (iTXB2) has been identified in the plasma of the Atlantic stingray, Dasyatis sabina (0.57±0.03 ng/ml). Plasma levels of iTXB2 increase if the blood is allowed to clot (3.0±0.27 ng/ml). When clotting occurs in the presence of indomethacin, this increase is partially inhibited (1.5±0.17 ng/ml), indicating the presence of a cyclooxygenase activity. Radioligand binding analysis using the TXA2 analog BOP binding was displaced by the TXA2 receptor (TP receptor) agonists U46619 (IC50=106.4±15.7 nM) and U44069 (IC50=88.7±13.0 nM), and the antagonist SQ29548 (IC50=51.0±12.9 nM). Binding was also displaced stereoselectively by the antagonists (-)L657925 (IC50=18.9±3.8 nM) and (+)L657926 (IC50=2025±280 nM). Tissue bath studies revealed that U46619, a stable TXA2 mimetic, elicited concentration-dependent contractions in the ventral aorta which were inhibited in a concentration-dependent manner by the TP receptor antagonist SQ29548. Using a human TP receptor riboprobe, Northern blotting of mRNA isolated from the stingray kidney identified transcripts of 2.8 and 6 kb. The 2.8 kb transcript is similar to a 2.8 kb transcript found in human cells or tissues, but the 6 kb transcript may be unique. These data indicate the presence of a TXB2-like substance in the blood, a TP receptor in the kidney, TXA2 biological activity in the ventral aorta, and expression of a TP receptor-like gene.