Endothelial cells which form the innermost layer of blood vessels secrete many vasoactive substances. The formation and functions of some of these vasoactive substances are proposed in the following statements: A. Prostacyclin produced by the endothelial cells promotes vasoconstriction. B. Inhibitors of the cyclooxygenase increase the production of prostacyclin. C. When endothelial cells are stimulated by acetylcholine or serotonin, nitric oxide (NO) is released that causes relaxation of vascular smooth muscle. D. NO is short-lived and inactivated by haemoglobin. Which one of the following options represents the combination of correct statements?
C and D
Endothelial Cell Vasoactive Substances Analysis
Endothelial cells, which form the inner lining of blood vessels, play a crucial role in regulating vascular tone and function by producing and releasing various vasoactive substances. These substances can cause either vasoconstriction (narrowing of blood vessels) or vasodilation (widening of blood vessels).
Let's evaluate each statement provided:
- Statement A: Prostacyclin produced by the endothelial cells promotes vasoconstriction.
Analysis: Prostacyclin (PGI${_2}$) is a potent vasodilator. It relaxes vascular smooth muscle, leading to vasodilation. It also inhibits platelet aggregation. Therefore, this statement is incorrect.
- Statement B: Inhibitors of the cyclooxygenase increase the production of prostacyclin.
Analysis: Cyclooxygenase (COX) enzymes are essential for the synthesis of prostaglandins, including prostacyclin, from arachidonic acid. Inhibiting COX enzymes would therefore decrease or block the production of prostacyclin, not increase it. Therefore, this statement is incorrect.
- Statement C: When endothelial cells are stimulated by acetylcholine or serotonin, nitric oxide (NO) is released that causes relaxation of vascular smooth muscle.
Analysis: Substances like acetylcholine and serotonin can stimulate endothelial cells to activate endothelial nitric oxide synthase (eNOS). eNOS produces nitric oxide (NO). NO diffuses to the underlying vascular smooth muscle cells, where it causes relaxation, leading to vasodilation. This mechanism is known as endothelium-dependent relaxation. Therefore, this statement is correct.
- Statement D: NO is short-lived and inactivated by haemoglobin.
Analysis: Nitric oxide (NO) is a highly reactive molecule with a very short half-life in biological systems. It is rapidly inactivated, primarily by reacting with haemoglobin and other heme-containing proteins, which effectively scavenges NO. This rapid inactivation is important for localizing its effects. Therefore, this statement is correct.
Based on the analysis, statements C and D are correct.
Important Questions from Cell signaling
In the table below Column A lists ligands and Column B lists classes of receptors
Column A Column B A Serotonin i Binding activates a G-protein which activates or inhibits an enzyme that generates a specific second messenger and opens ion channel B Interferons ii Binding causes receptor monomers to dimerize. Dimeric receptor then interacts with and activates one or more cytosolic tyrosine protein kinases C Glycine iii Binding changes the conformation of the receptor so that specific ions flow through it D Insulin iv Binding leads to activation of intrinsic tyrosine kinase activity Which one is the correct match?
Receptor for which one of the following proteins spans the plasma membrane of target cells but DOES NOT contain intrinsic protein kinase activity?
Which one of the following amino acids is characteristic of and is conserved in response regulator of plant two-component systems?
Which one of the following signaling molecules is NOT a protein or a peptide?
Receptor tyrosine kinases (RTKs) form a large and important class of cell surface receptors whose ligands are soluble or membrane bound protein or peptide hormones. Which of the following statement is INCORRECT?
