Upregulation of endothelin B receptors in kidneys of DOCA-salt hypertensive rats

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Abstract
Experiments were designed to elucidate the role of endothelin B receptors (ETB) on arterial pressure and renal function in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Male Sprague-Dawley rats underwent uninephrectomy and were treated with either DOCA and salt (0.9% NaCl to drink) or placebo. DOCA-salt rats given the ETB-selective antagonist, A-192621, for 1 wk (10 mg ⋅ kg−1⋅ day−1in the food) had significantly greater systolic arterial pressure compared with untreated DOCA-salt rats (208 ± 7 vs. 182 ± 4 mmHg) whereas pressure in placebo rats was unchanged. In DOCA-salt, but not placebo rats, A-192621 significantly decreased sodium and water excretion along with parallel decreases in food and water intake. To determine whether the response in DOCA-salt rats was due to increased expression of ETBreceptors, endothelin receptor binding was performed by using membranes from renal medulla. Maximum binding (Bmax) of [125I]ET-1, [125I]ET-3, and [125I]IRL-1620 increased from 227 ± 42, 146 ± 28, and 21 ± 1 fmol/mg protein, respectively, in placebo rats to 335 ± 27, 300 ± 38, and 61 ± 6 fmol/mg protein, respectively, in DOCA-salt hypertensive rats. The fraction of receptors that are the ETBsubtype was significantly increased in DOCA-salt (0.88 ± 0.07) compared with placebo (0.64 ± 0.01). The difference between [125I]ET-3 and [125I]IRL-1620 binding is consistent with possible ETBreceptor subtypes in the kidney. These results indicate that ETBreceptors in the renal medulla are up-regulated in the DOCA-salt hypertensive rat and may serve to maintain a lower arterial pressure by promoting salt and water excretion.

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