Abstract 33: Participation of Prostaglandin E2 and EP4 Receptors in Connecting Tubule Glomerular Feedback (CTGF).

Abstract

The afferent arteriole (Af-Art) accounts for most of renal vasculature resistance, thus controlling glomerular filtration rate. The connecting tubule (CNT) is in close contact with the Af-Art. Connecting tubule glomerular feedback (CTGF) is a mechanism in which Na reabsorption in the CNT causes Af-Art dilation. We have shown that CTGF is mediated by eicosanoids, including prostaglandins and epoxyeicosatrienoic acids (EETs), however their exact source and nature remain unknown. Here we tested the hypothesis that during CTGF the CNT releases prostaglandin E 2 (PGE 2 ), which binds EP4 receptors and dilates the Af-Art. Rabbit Af-Arts with the adherent CNT intact were microdissected and perfused. The Af-Arts were preconstricted with norepinephrine. CTGF was elicited by increasing luminal NaCl in the CNT from 10 to 80 mM. To identify the source of the vasodilator prostaglandins we first disrupted the vascular endothelium by adding anti-Factor-VIII antibody to the Af-Art lumen. This did not affect CTGF (control: 7.9±0.9, endothelium disrupted: 8.6±0.6 μm, n=7). We then added arachidonic acid (AA) to the lumen of the CNT while maintaining zero NaCl in the perfusate, and found that AA caused dose-dependent dilation of the attached Af-Art (from 7.9±2.2 to 15.5±1.3 μm, P <0.01, n=4). This cannot be explained by AA diffusing to the Af-Art because AA is a vasoconstrictor for the Af-Art. Taken together, these data indicate that CTGF-induced vasorelaxation is endothelium-independent, and that prostaglandins originate from the CNT. To study which specific prostaglandin and receptor mediate CTGF, we added the EP4 receptor blocker L161982 (10 μM) to the bath in the presence of the EET synthesis inhibitor MS-PPOH. EP4 receptor blockade abolished CTGF (control: 8.5±0.9, MS-PPOH+L161982: 0.8±0.4μm, P <0.001, n=6). To confirm these results we used a different, specific EP4 blocker, ONO-AE-208 (100 nM), which also abolished CTGF (control: 9.4±0.5, MS-PPOH+ONO-AE-208: -0.6±0.2 μm, P <0.001, n=6). We conclude that increasing luminal Na stimulates release of prostaglandin E 2 from the CNT, which acts on EP4 on the Af-Art inducing endothelium-independent dilation during CTGF. Our studies provide a better understanding of the mechanisms by which CTGF controls Af-Art resistance.