ROLE OF ENDOTHELIN IN THE DEVELOPMENT OF DAHL HYPERTENSION

To evaluate the possible role of endothelin in the development and/or maintenance of hypertension in Dahl rats, we examined the responsiveness of isolated vascular smooth muscle and glomerular mesangial cells, as well as deendothelialized vascular ring preparations to endothelin-1 (ET-1). Production of immunoreactive endothelin (ir-ET) was studied in freshly isolated glomeruli and renal medullary slices. Both glomerular mesangial cells and vascular smooth muscle cells obtained from prehypertensive Dahl-S rats exhibited an exaggerated [Ca2+]i response to ET-1, as compared with cells obtained from Dahl-R rats. This was paralleled by the enhanced isometric contraction of vascular rings obtained from pre-hypertensive Dahl-S rats. ir-ET production was doubled in response to 0.1 mM ouabain in tissue samples obtained from prehypertensive Dahl-S, but not Dahl-R rats. This effect was not observed in tissues obtained from animals fed a 4% NaCl diet (hypertensive). Immunocytochemistry of ET distribution in the outer medullary stripe showed approximately a 40% higher fluorescence intensity in sections obtained from Dahl-S rats fed 4% NaCl diet as compared with Dahl-R rats fed the same diet. Northern blot analysis of poly(A)+RNA extracted from medullae of prehypertensive Dahl-S and -R rats using a full-length cDNA probe for rat ET-1 revealed a marginal induction of pre-pro-ET-1 message in Dahl-S samples after 30 and 60 min of incubation with 0.1 mM ouabain. In conclusion, increased responsiveness of target cells to ET-1 and inducibility of ir-ET production in prehypertensive Dahl-S rats are in favor of a possible role of this peptide in the pathogenesis of Dahl hypertension. We hypothesize that ouabain-like factor(s) may trigger production of ET, thus serving as a link between high-salt intake and the development of hypertension in Dahl-S rats.