Endothelin binding in brain of normotensive and spontaneously hypertensive rats

The endothelins (ETs) are a recently discovered family of peptides which appear to be involved in hemodynamic regulation; they have potent vasoconstrictor properties and dose-related effects on blood pressure when administered peripherally. Little is known about the role of ET in the brain. The purpose of this study was to characterize the binding properties of various ETs in the brain of normotensive (Wistar-Kyoto) and hypertensive (spontaneously hypertensive) rats. [125I]ET 1 was prepared using the enzymobead lactoperoxidase method and purified by high-pressure liquid chromatography. Membrane fractions were prepared from homogenates of various brain regions. A differential distribution of ET binding was found among the 14 brain regions studied. The cerebellum, brainstem and area postrema/nucleus tractus solitarius had the highest binding, whereas the cortex, pituitary and septum had the least binding. Competition experiments performed with hypothalamus, brainstem and cerebellum demonstrated different Ki values for the ET studied. ET 2 had the highest affinity with a Ki of 4 x 10(-1) M, whereas the ET analog, Ala3,11-ET 1, had the lowest affinity with a Ki of 3 x 10(-10) M. Saturation experiments indicated a single class of high-affinity receptors in cerebellar (Kd = 2.5 x 10(-11) M, maximal binding Bmax = 1.25 x 10(-12) mol/mg) and hypothalamic membranes (Kd = 1.9 x 10(-11) M, Bmax = 0.93 x 10(-12) mol/mg). No differences in Kd or Bmax were detected between Wistar-Kyoto and spontaneously hypertensive rats hypothalamic and cerebellar tissues. The results of this study suggest a role for ET in the brain, but revealed no differences between normotensive and hypertensive strains.