1. In the present study we investigated, first, the effects of high Na+ intake and, second, the effects of water deprivation on plasma endothelin-1 concentration and urinary endothelin-1 excretion and on endothelin receptors in membranes of renal glomeruli and papillae and of aortic smooth muscle and lung tissue from 32 female Sprague-Dawley rats.
2. After 5 weeks of high Na+ intake (n = 8) urinary Na+ excretion was 10.5 + 1.3 compared with 1.6 + 0.2 mmol/24h in controls. Body weight, plasma osmolality, plasma endothelin-1 concentration (23 + 6 versus 28 + 3 fmol/ml) and urinary endothelin-1 excretion (6.1 + 13 versus 4.7 + 0.3 pmol/24 h) remained unchanged.
3. The characteristics of endothelin-1 receptors in glomeruli, papillae, aortic smooth muscle and lung tissue from salt-loaded rats were not different from those of controls.
4. After 48 h water deprivation (n = 8) body weight had decreased, whereas packed cell volume and plasma and urine osmolalities had increased compared with controls (n = 8) (P <0.05). Plasma endothelin-1 concentration (40 + 6 versus 21 + 2 fmol/ml) was higher (P <0.01) and urinary endothelin-1 excretion (1.0 + 0.2 versus 2.8 + 03 pmol/24 h) was lower than in controls (P <0.01).
5. Water deprivation was accompanied by increases in endothelin-1 binding sites in glomeruli (Bmax. 4.8 + 0.4 versus 3.6 + 0.2 pmol/mg of protein; P <0.05) with unchanged receptor affinity (Kd 56 + 9 versus 57 + 8 pmol/l), in papillae (Bmax. 8.0 + 0.7 versus 6.2 + 0.5 pmol/mg of protein; P <0.05) with unchanged Kd (78 + 6 versus 63 + 4 pmol/l) and in aortic smooth muscle cells (Bmax. 3.5 + 0.2 versus 2.8 + 0.2 pmol/mg of protein; P <0.05) in which Kd rose to 307 + 27 versus 180 + 22 pmol/l (P <0.05). Endothelin-1 receptors in lung tissue were unaltered (Bmax. 10.0 + 03 versus 103 + 0.8 pmol/mg of protein; Kd 152 + 12 versus 137 + 14 pmol/l).
6. Our results suggest that the peripheral endothelin-1 system may play a role in the adaptation to changes in body water content rather than in Na+ balance.
