Upregulation of endothelin-1 binding in tissues of salt-loaded stroke-prone spontaneously hypertensive rats.

Upon maintained on a 1% NaCl drinking solution beginning at 7 weeks of age, the stroke-prone spontaneously hypertensive rat (SHRsp) developed severe hypertension and stroke; most died by 16 weeks. The mechanism by which these diseases evolve remains unclear. Endothelin-1 (ET-1) is a potent, peptidic vasoconstrictor and is implicated in the pathogenesis of various cardiovascular, renal, and central nervous system diseases. The purpose of the present study was to compare the binding of [125I]ET-1 to the brain, heart, kidney, liver, and spleen membrane preparations of 16-week-old SHRsp and age-matched normotensive Wistar-Kyoto rats (WKY). The KD values for [125I]ET-1 binding to the corresponding tissues of the two strains were not significantly different, except in the brain (SHRsp: 17 +/- 1 pM; WKY: 24 +/- 1 pM). In contrast, the Bmax values measured in the brain, heart, kidney, and liver of SHRsp were 1.5- to 2.1-fold greater than those of their WKY counterparts. Competition of [125I]ET-1 binding to the membrane preparations by the specific ETA receptor antagonist BQ-123 or the specific ETB receptor agonist sarafotoxin S6c revealed a similar proportion of ETA and ETB receptor subtypes in the corresponding tissues of the two rat strains. These results indicate that ET-1 binding is upregulated in SHRsp and suggest that ET-1 may play a pathophysiological role in this animal model of genetic hypertension.