The adrenomedullary venous vasculature as a target for endothelins: comparison of the porcine and bovine central adrenomedullary veins

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Endothelin regulation of adrenal function

1. The goal of the present review is to recount the evidence that endothelin (ET) has a significant influence on the peripheral sympathetic nervous system by regulating the function of the adrenal medulla. 2. The presence of an active ET system in the adrenal medulla has been clearly demonstrated. Endothelin protein, mRNA, binding sites and ET-converting enzyme have been identified in adrenal tissue and medullary chromaffin cells, suggesting that this peptide may contribute to the regulation of adrenal medullary function. 3. Studies investigating the function of ET in the adrenal gland have demonstrated that ET has a stimulatory effect on the adrenal medulla. Endothelin elicits an increase in catecholamine release from perfused intact adrenal glands as well as from cultured chromaffin cells. This effect has been shown to be mediated by ETA and ETB receptors. 4. The mechanism by which ET causes an increase in catecholamine release from the adrenal medulla appears to be independent of cholinergic activation of chromaffin cells. Endothelin has been shown to act directly at chromaffin cells to increase intracellular calcium, which results in catecholamine release. 5. Endothelin can indirectly affect catecholamine release by its effect on adrenal blood flow. Studies indicate that ET has both vasoconstrictor and vasodilator effects in the adrenal gland, which suggests a role for ET in the regulation of adrenal blood flow. Endothelin has also been proposed to participate in the selective contraction of the adrenomedullary veins, which enhances the discharge of catecholamines from the adrenal gland during activation.