Mesangial cells are specialized contractile cells located within the glomerulus of the kidney, regulating capillary blood flow and filtration surface area. Their ability to contract or relax modulates glomerular filtration rate and renal blood flow, playing a vital role in kidney function.

Overview of Mesangial Cell Contraction and Relaxation

Mesangial cell contraction reduces glomerular capillary surface area, decreasing filtration, while relaxation increases capillary diameter and filtration. Contractility depends on intracellular calcium levels and is affected by vasoactive substances. Relaxation is often mediated by cyclic nucleotides like cAMP and cGMP, as well as by vasodilatory factors.pubmed.ncbi.nlm.nih+1

Agents Affecting Mesangial Cells

1. Histamine

   • Primarily a vasoactive mediator causing contraction of mesangial cells through elevated intracellular calcium.

   • Generally associated with contraction and pro-inflammatory responses.sciencedirect

2. Thromboxane A2

   • A potent vasoconstrictor and platelet aggregator.

   • Promotes mesangial cell contraction via G-protein coupled receptor signaling and calcium mobilization.sciencedirect

3. Norepinephrine

   • Acts through alpha-adrenergic receptors.

   • Stimulates contraction of mesangial cells by increasing intracellular calcium and activating vasoconstrictive pathways.sciencedirect

4. Dopamine

   • Acts as a vasodilator in the renal circulation.

   • Causes relaxation of mesangial cells by increasing intracellular cAMP or cGMP levels, leading to decreased intracellular calcium and cell relaxation.

   • Dopamine reduces mesangial cell tone, promoting increased glomerular blood flow.revistanefrologia+2

Physiological Significance

Dopamine’s role in mesangial cell relaxation helps maintain optimal glomerular filtration and renal blood flow, especially in conditions demanding enhanced filtration. In contrast, agents like histamine, thromboxane A2, and norepinephrine contribute to vasoconstriction and reduced filtration.

Conclusion

Among the given agents, dopamine is the one that causes relaxation of mesangial cells.

Correct answer: (4) Dopamine