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The following statements are made for the effect of hormones on the glomerular filtration rate (GFR):

A. Norepinephrine, epinephrine, and endothelin constrict renal blood vessels and decrease GFR.
B. Endothelin dilates renal blood vessels to increase GFR.
C. Norepinephrine and endothelin constrict renal blood vessels and decrease GFR, while epinephrine dilates renal blood vessels to increase GFR.
D. Prostaglandin (PGE₂) and bradykinin decrease renal vascular resistance and increase GFR.

Correct option is D

Statement A: "Norepinephrine, epinephrine, and endothelin constrict renal blood vessels and decrease GFR."  (Correct)

• Norepinephrine (NE) and epinephrine (from the sympathetic nervous system and adrenal medulla) cause vasoconstriction of renal arteries, reducing renal blood flow (RBF) and GFR.
• Endothelin, a potent vasoconstrictor, is released in response to stress and injury, further reducing GFR.
  

Statement B: "Endothelin dilates renal blood vessels to increase GFR."  (Incorrect)

• Endothelin is a vasoconstrictor, not a vasodilator.
• It reduces renal blood flow and GFR, particularly in disease conditions (e.g., acute kidney injury).
  

Statement C: "Norepinephrine and endothelin constrict renal blood vessels and decrease GFR, while epinephrine dilates renal blood vessels to increase GFR."  (Incorrect)

• The first part is correct (NE and endothelin cause vasoconstriction).
• However, epinephrine does not always dilate renal blood vessels.
  • At low doses, epinephrine increases renal perfusion slightly.
  • At high doses, epinephrine causes vasoconstriction, decreasing renal blood flow and GFR.
• Since epinephrine’s effect is dose-dependent, the statement is not fully correct.
  

Statement D: "Prostaglandin (PGE₂) and bradykinin decrease renal vascular resistance and increase GFR."  (Correct)

• Prostaglandins (PGE₂, PGI₂) are vasodilators that help maintain GFR by counteracting excessive vasoconstriction caused by angiotensin II and norepinephrine.
• Bradykinin is also a vasodilator that increases renal blood flow and GFR.
  

Information Booster

Here are some key concepts related to hormonal regulation of GFR:

1. Vasoconstrictors (Decrease GFR & Renal Blood Flow):

   • Norepinephrine & Epinephrine (sympathetic activation) → constrict afferent arterioles, reducing GFR.
   • Endothelin → a powerful vasoconstrictor, reducing renal blood flow.
   • Angiotensin II → at high levels, it constricts efferent arterioles, reducing GFR.

2. Vasodilators (Increase GFR & Renal Blood Flow):

   • Prostaglandins (PGE₂, PGI₂) → dilate renal arterioles, preventing excessive vasoconstriction.
   • Bradykinin → increases renal perfusion and GFR.
   • Atrial Natriuretic Peptide (ANP) → dilates afferent arterioles, increasing GFR.

3. Epinephrine’s Role:

   • Low doses → mild dilation of renal vessels, increasing GFR.
   • High doses → vasoconstriction, reducing renal blood flow and GFR.

4. Glomerular Filtration Regulation:

   • Autoregulation mechanisms (myogenic response, tubuloglomerular feedback) help stabilize GFR.
   • Hormonal control fine-tunes filtration based on the body's needs.

5. Clinical Relevance:

   • Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandins, potentially reducing GFR.
   • ACE inhibitors (e.g., enalapril) block angiotensin II, preventing excessive vasoconstriction.