Interactions between endothelin-1 and the renin-angiotensin-aldosterone system.

The renin-angiotensin-aldosterone (RAA) system and the endothelin (ET) system entail the most potent vasopressor mechanisms identified to date. Although they were studied in depth in relation to arterial hypertension and cardiovascular diseases, limited information on their interrelationships in causing hypertension and related target organ damage exists. The identification of consensus sequences for jun in the regulatory region of the preproendothelin-1 (ppET-1) gene raised the possibility of its transcriptional regulation by angiotensin II (Ang II). This was confirmed by the finding that stimulation with Ang II of cultured vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) induced expression of the ppET-1 gene and synthesis of ET-1. Endogenously produced ET-1 was found to contribute to the hypertrophic response of cardiomyocytes to Ang II and thereby to cardiac hypertrophy. Furthermore, ET-1 exerts multifaceted effects on the RAA system, such as dose-dependent inhibition of renin synthesis, and stimulation of aldosterone secretion. The finding of abundant specific ET-1 receptors in the adrenocortical zona glomerulosa (ZG) suggested a direct secretagogue effect of ET-1. In rats, ETB receptors mediate such an effect, whilst in humans, both ETA and ETB receptor subtypes intervene in regulating the transcription of the aldosterone synthase gene. In addition, ET-1 stimulates DNA synthesis and proliferation of ZG cells via ETA receptors and, therefore, might play a role in cell turnover of the normal adrenal cortex and in the onset of adrenal tumours. Studies on the in vivo interactions between ETs and the RAA system have given conflicting results, insofar as some suggested a participation of ET-1 in the pressor and cellular effects of exogenously administered Ang II, whereas others did not in the transgenic TGR(Ren 2m)27 rats and in the two-kidney, one clip.