Concomitant expression of receptor subtype and isopeptide of endothelin by human adrenal gland

We studied whether specific receptors for endothelin (ET) isopeptide exist in human aldosterone-producing adenoma and normal adrenal cortex, and whether ET isopeptides are produced by human adrenal gland. Competitive binding studies using [¹²⁵I]ET-1 as a radioligand revealed the presence of a single class of high-affinity binding sites for ET-1 with the apparent Kd of 70 ± 31 pM and B_max of 226 ± 139 fmol/mg protein in adenoma membranes almost comparable to those in adjacent normal cortex. The apparent K_i for ET-2 and ET-3 were 89 ± 33 pM and 82 ± 16 pM, respectively. Northern blot analysis of poly(A)⁺ RNA of adenoma and adjacent normal cortex using cDNAs for ET receptor subtype (ETa, ETb) and ET isopeptide (ET-1, ET-3) as probes revealed that ETa and ETb receptors as well as ET isopeptides (prepro-ET-1, preproET-3) are concomitantly expressed in both tissues. Our data demonstrate for the first time that ET receptor subtype (ETa and ETb) and ET isopeptide (ET-1 and ET-3) are concomitantly expressed by human adrenal cortex, suggesting the potential role of ETs as a local mediator in human adrenal gland.