RAT RENAL, AORTIC AND PULMONARY ENDOTHELIN-I RECEPTORS - EFFECTS OF CHANGES IN SODIUM AND WATER-INTAKE

1. In the present study we investigated, first, the effects of high Na + intake and, second, the effects of water deprivation on plasma endot helin-1 concentration and urinary endothelin-1 excretion and on endoth elin receptors in membranes of renal glomeruli and papillae and of aor tic 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/24 h in controls. Body weight, p lasma osmolarity, plasma endothelin-1 concentration (23+/-6 versus 28/-3 fmol/ml) and urinary endothelin-1 excretion (6.1+/-1.3 versus 4.7/-0.3 pmol/24 h) remained unchanged. 3. The characteristics of endothe lin-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, whe reas packed cell volume and plasma and urine osmolarities had increase d compared with controls (n=8) (P<0.05). Plasma endothelin-I concentra tion (40+/-6 versus 21+/-2 fmol/ml) was higher (P<0.01) and urinary en dothelin-1 excretion (1.0+/-0.2 versus 2.8+/-0.3 pmol/24 h) was lower than in controls (P<0.01). 5. Water deprivation was accompanied by inc reases in endothelin-I binding sites in glomeruli (B(max.) 4.8+/-0.4 v ersus 3.6+/-0.2 pmol/mg of protein; P<0.05) with unchanged receptor af finity (K(d) 56+/-9 versus 57+/-8 pmol/l), in papillae (B(max.) 8.0+/- 0.7 versus 6.2+/-0.5 pmol/mg of protein; P<0.05) with unchanged K(d) ( 78+/-6 versus 63+/-4 pmol/l) and in aortic smooth muscle cells (B(max. ) 3.5+/-0.2 versus 2.8+/-0.2 pmol/mg of protein; P<0.05) in which K(d) rose to 307+/-27 versus 180+/-22 pmol/l (P<0.05). Endothelin-1 recept ors in lung tissue were unaltered (B(max.) 10.0+/-0.5 versus 10.3+/-0. 8 pmol/mg of protein; K(d) 152+/-12 versus 137+/-14 pmol/l). 6. Our re sults suggest that the peripheral endothelin-1 system may play a role in the adaptation to changes in body water content rather than in Nabalance.