ENDOTHELIN-1 AND ITS RECEPTOR-A AND RECEPTOR-B IN HUMAN ALDOSTERONE-PRODUCING ADENOMAS

Endothelin-1 stimulates aldosterone secretion by interacting with spec ific receptors. Accordingly, we wished to investigate endothelin-1, en dothelin-A (ET(A)) receptor, and endothelin-B (ET(B)) receptor gene ex pression, localization, and properties in aldosterone-producing adenom as and in the normal human adrenal cortex. We carried out I-125-endoth elin-1 displacement studies with cold endothelin-1, endothelin-3, the specific ET(A) antagonist BQ-123, and the specific ET(B) weak agonist sarafotoxin 6 C and coanalyzed data with the nonlinear iterative curve -fitting program LIGAND. We also studied gene expression with reverse transcription-polymerase chain reaction with specific primers for endo thelin-1, ET(A), and ET(B) complementary DNA. Normal adrenal cortices from consenting kidney cancer patients (n=2) and aldosterone-producing adenomas (n=4) were studied; for the latter, surrounding normal corte x and kidney biopsy tissue served as controls. To further localize the receptor subtypes, tissue sections were studied by autoradiography in the presence and absence of 500 nmol/L BQ-123, 100 nmol/L sarafotoxin 6 C, and 1 mu mol/L cold endothelin-1. In all tissues examined, endot helin-1, ET(A), and ET(B) messenger RNAs were easily detected. However , in aldosterone-producing adenomas, both receptors' genes were expres sed at a higher level than in the kidney. In aldosterone-producing ade nomas (F=9.49, P<.01) as well as in the normal adrenal cortex (F=8.57, P<.01), but not in adrenocortical tissue surrounding aldosterone-prod ucing adenomas (F=5.08, P=NS), the significantly best fitting of bindi ng data was provided by a two-site model indicating the presence of tw o receptor subtypes with density (B-max) and affinity (K-d) similar to those previously found in other tissues. Autoradiography confirmed th e presence of both ET(A) and ET(B) receptors on normal zona glomerulos a cells as well as on aldosterone-producing adenoma cells. Thus, the g enes of endothelin-1 and of its receptors, ET(A) and ET(B), are active ly transcribed in the human adrenal cortex, and both receptor subtypes are translated into proteins in zona glomerulosa and aldosterone-prod ucing adenoma cells. These data are consistent with an autocrine parac rine role of endothelin-1 in the regulation of aldosterone secretion, both under normal conditions and in aldosterone-producing adenomas.