Chronic ouabain treatment induces vasa recta endothelial dysfunction in the rat

Area of Science:

• Nephrology
• Cardiovascular Physiology
• Cellular Biology

Background:

• Descending vasa recta (DVR) are crucial for renal medulla perfusion.
• Ouabain is known to modulate endothelial cytoplasmic calcium signaling ([Ca(2+)](CYT)) in DVR.

Purpose of the Study:

• To investigate the expression of the ouabain-sensitive Na-K-ATPase alpha2 subunit in rat renal vasculature.
• To determine the effects of acute and chronic ouabain exposure on DVR function and endothelial signaling.

Main Methods:

• Immunostaining to verify alpha2 subunit expression in DVR pericytes and endothelium.
• Microperfusion studies to assess DVR responses to acetylcholine, angiotensin II, and L-NAME.
• Generation of ouabain-hypertensive (OH) rats via chronic ouabain treatment.
• Measurement of endothelial [Ca(2+)](CYT) responses to ouabain, acetylcholine, and bradykinin in OH rats.

Main Results:

• Alpha2 subunit expression confirmed in DVR endothelium and pericytes.
• Acute ouabain (100-500 nM) augmented acetylcholine-stimulated nitric oxide generation; higher concentrations (1 mM) caused constriction.
• Chronic ouabain treatment induced hypertension and abolished acute ouabain-induced [Ca(2+)](CYT) elevation in DVR endothelium.
• DVR endothelial responses to acetylcholine (low concentration) and bradykinin were attenuated in OH rats.

Conclusions:

• Endothelial responses may counteract acute ouabain-induced DVR vasoconstriction.
• Chronic in vivo ouabain exposure leads to hypertension and DVR endothelial dysfunction, impairing vasodilatory signaling.