True regarding endothelin-1 are all except
**Core Concept**
Endothelin-1 (ET-1) is a potent vasoconstrictor peptide produced by the endothelium, playing a crucial role in vascular tone regulation. It is a member of the calcitonin gene-related peptide family and exerts its effects through two main receptor subtypes: ETA and ETB.
**Why the Correct Answer is Right**
Endothelin-1 acts by binding to its receptors on the smooth muscle cells of blood vessels, leading to vasoconstriction and an increase in blood pressure. This is mediated through a G-protein coupled receptor pathway, which ultimately results in the activation of phospholipase C and the release of intracellular calcium. ET-1 also has a role in promoting cell proliferation and migration, which is involved in the pathogenesis of various diseases, including atherosclerosis and pulmonary hypertension.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because ET-1 is not primarily involved in vasodilation, although it can have some vasodilatory effects under certain conditions, such as in the presence of endothelial dysfunction.
* **Option B:** This option is incorrect because ET-1 is not primarily involved in the regulation of cardiac function, although it can have some effects on cardiac contractility and rhythm.
* **Option C:** This option is incorrect because ET-1 is not primarily involved in the regulation of renal function, although it can have some effects on renal blood flow and glomerular filtration rate.
**Clinical Pearl / High-Yield Fact**
Endothelin-1 is a key player in the pathogenesis of pulmonary arterial hypertension, and its levels are often elevated in patients with this condition. Inhibition of the ETA receptor has been shown to be an effective treatment strategy for this disease.
**Correct Answer:** C.