Abstract P344: Increased Expression and Function of Endothelin Receptors in Aorta of (mRen2)27 Hypertensive Rats

Endothelin-1 (ET-1) contributes to various cardiovascular diseases including hypertension. ET-1 is produced in the endothelium and acts via ET A receptors, located in smooth muscle cells, and via ET B receptors, located in both endothelium and smooth muscle cells. Activation of ET A produces vasoconstriction, whereas endothelial ET B activation mediates vasodilation, with previous studies showing that ET-1-mediated vasoconstriction is enhanced in hypertension. We hypothesized that increased ETA-mediated function is present in vasculature of the (mRen2)27 hypertensive rat. Western blotting of total protein extracts from thoracic aorta was used to determine expression of ET A and ET B from Sprague-Dawley (SD n=4) and (mRen2)27 hypertensive (n=5) rats. Specificity of western blot signals for ET A and ET B was assessed by using pre-absorption of primary antibody with the corresponding antigenic peptide and intensity of signals was measured by densitometry (NIH-J Image). Contractile responses to ET-1 (10 -11 -10 -7 M) in intact and denuded aorta were determined by wire myography (Multi Myograph, DMT-USA) in the presence of the ET A blocker BQ123 (10 -6 M) or the ET B blocker BQ788 (10 -6 M). Contraction to ET-1 was expressed as maximal response (ET MAX as %K MAX ) and sensitivity (pD 2 =-Log [EC 50 ]). In aortae from (mRen2)27 rats ET A and ET B receptor expression (48 and 31 kDa bands) was greater relative to aortae of SD rats (p<0.05). ET-1 contraction showed increased sensitivity in (mRen2)27 vs SD aortae (pD 2 , 8.17±0.15 vs 7.76±0.12, p<0.05) with similar ET MAX (157±16 vs 145±6 %K MAX , p>0.05). In intact arteries, blockade of ET B increased ET-1 sensitivity (pD 2 8.4±0.3, p<0.05) in SD without effect on intact arteries from (mRen2)27 rats. In denuded arteries, ETB blockade increased ET MAX only in aortae from (mRen2)27 (205±12 vs 152±5, p<0.05). Thus, increased ET A expression mediates greater ET-1-dependent contraction in vasculature of (mRen2)27 rats. In (mRen2)27 rats, loss of endothelial ET B receptor function in intact arteries may contribute to enhanced constrictor responses to ET-1, whereas increased ET B receptors in smooth muscle cells provide a counterbalancing vasodilation to offset maximal contractile effects of ET-1 in this model of hypertension.