The glomerular ultrafiltration coefficient (Kf) can be changed by the mesangial cells producing a decrease in Kf largely due to a reduction in the area available for filtration. The following statements are made about some agents that affect the mesangial cells:

• A. Norepinephrine causes contraction of mesangial cells.
• B. Angiotensin II causes relaxation of mesangial cells.
• C. Histamine causes relaxation of mesangial cells.
• D. Atrial natriuretic factor (ANF) causes relaxation of mesangial cells.

Which one of the following options represents the combination of all correct statements?

Correct option is D

Detailed Explanation:

Statement A: Norepinephrine causes contraction of mesangial cells.

• Correct: Norepinephrine causes contraction of mesangial cells via alpha-1 adrenergic receptors, which reduces the surface area for filtration. This ultimately leads to a decrease in the glomerular filtration rate (GFR). This effect helps in regulating blood pressure.

Statement B: Angiotensin II causes relaxation of mesangial cells.

• Incorrect: Angiotensin II causes contraction of mesangial cells, not relaxation. It binds to AT1 receptors and triggers the contraction of mesangial cells, which reduces the filtration surface area and subsequently lowers the glomerular filtration rate (GFR).

Statement C: Histamine causes relaxation of mesangial cells.

• Incorrect: Histamine does cause relaxation of mesangial cells, but it also works as a vasodilator that helps increase the glomerular filtration rate (GFR). However, it is important to note that this statement contradicts Statement B, as histamine works in opposition to Angiotensin II, which is a vasoconstrictor.

Statement D: Atrial natriuretic factor (ANF) causes relaxation of mesangial cells.

• Correct: ANF (Atrial natriuretic factor) also causes relaxation of mesangial cells by binding to NPR-A receptors and increasing glomerular filtration. This is another mechanism that helps in sodium and fluid balance by increasing the surface area for filtration and raising GFR.

Correct Answer:

• Option 4 (A and D) is the correct answer because Statement A and Statement D are both correct:
  • Statement A: Norepinephrine causes contraction of mesangial cells.
  • Statement D: ANF causes relaxation of mesangial cells.

Information Booster:

1. Norepinephrine works by constricting mesangial cells, which reduces the surface area for filtration.
2. ANF works by relaxing mesangial cells, thus increasing the filtration area and increasing GFR.
3. Angiotensin II has the opposite effect of ANF; it causes contraction of mesangial cells, leading to a reduction in the glomerular filtration rate.
4. Histamine, while causing relaxation, works in a manner that contrasts with Angiotensin II and increases filtration by relaxing mesangial cells.