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

Area of Science:

• Marine biology
• Biochemistry
• Pharmacology

Background:

• Thromboxane A2 (TXA2) is a potent mediator of platelet aggregation and vasoconstriction.
• Thromboxane B2 (TXB2) is the stable metabolite of TXA2.
• The presence and function of the TXA2 pathway in elasmobranchs remain largely unexplored.

Purpose of the Study:

• To investigate the presence and characteristics of thromboxane B2-like substance and its receptor in the Atlantic stingray (Dasyatis sabina).
• To determine the biological activity of TXA2 mimetics and antagonists in stingray tissues.
• To identify the expression of thromboxane-prostanoid (TP) receptor genes in stingray kidney.

Main Methods:

• Measurement of thromboxane B2-like immunoreactivity (iTXB2) in plasma.
• Radioligand binding assays using [125I]BOP to characterize the TXA2 receptor in kidney membranes.
• Tissue bath studies to assess the effects of TXA2 receptor agonists and antagonists on aortic contractions.
• Northern blotting to detect TP receptor mRNA transcripts in kidney tissue.

Main Results:

• Plasma iTXB2 levels increased upon blood clotting, indicating cyclooxygenase activity.
• A TXA2 receptor with specific binding affinities for agonists and antagonists was identified in kidney membranes.
• TXA2 mimetic U46619 caused concentration-dependent aortic contractions, inhibited by TP receptor antagonist SQ29548.
• Two TP receptor-like mRNA transcripts (2.8kb and 6kb) were detected in stingray kidney, with the 6kb transcript potentially being unique.

Conclusions:

• Atlantic stingrays possess a TXB2-like substance in their blood and a functional TP receptor in their kidneys.
• TXA2 signaling exhibits biological activity in stingray vasculature.
• The identification of TP receptor gene expression suggests a conserved role for this pathway in elasmobranchs.