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Mechanism of Drug Action > Renal pharmacology (Concepts) > Flashcards

Renal pharmacology (Concepts) Flashcards

1
Q

What are diuretics?

A

Drugs that increase urine output

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2
Q

What are the general mechanisms of diuretics?

A

Increased excretion of Na+, which causes an increased volume of accompanying urine in order to maintain osmotic pressure.

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3
Q

What are the classes of diuretics?

A
  1. Loop diuretics
  2. Thiazide diuretics
  3. K+-sparing diuretics
  4. Carbonic anhydrase inhibitors
  5. Osmotic diuretics
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4
Q

Which is the most powerful class of diuretic?

A

Loop diuretics

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5
Q

What are the mechanisms of action of loop diuretics?

A
  1. They act on the TAL of LoH and inhibit the action of the NKCC2 (Na+/K+/2Cl-) cotransporter, which is involved in reabsorption of Na+.
  2. In addition, they may also have venodilatory effects, which has 2 benefits:
    - Decreases MSFP and thus preload on heart
    - Reduces filtration fraction at glomerulus by causing dilation of efferent arterioles
  3. Weak inhibitory effect on carbonic anhydrase
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6
Q

What are the side effects of loop diuretics?

A
  1. Hypokalaemia: As a result of increased K+ excretion due increased absorption of Na+ in DCT through ENaC and thus K+ excretion through ROMK as result of increased –ve lumen potential.
  2. Increased excretion of Ca2+ and Mg2+ as their reabsorption is dependent on the +ve lumen potential set up by K+ recycling through ROMK, which is disrupted.
  3. Reduced uric acid excretion, leading to hyperuricaemia and acute gout.
  4. Excess water loss and reduction in ECF volume results in hypovolaemia and hypotension.
  5. Contraction metabolic alkalosis as a result of increased H+ excretion in DCT due to increased Na+ delivery, driving H+ secretion through NHE3.
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7
Q

Which part of the renal tubules do loop diuretics act on?

A

TAL of LoH

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8
Q

How can excess K+ loss be treated when using loop diuretics?

A
  1. Use in conjunction with K+-sparing diuretics
  2. Giving K+ supplements
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9
Q

What are the clinical uses of loop diuretics?

A
  1. Pulmonary oedema
  2. Chronic cardiac failure
  3. Ascites due to portal hypertension caused by liver cirrhosis
  4. Renal failure
  5. Nephrotic syndrome
  6. Hypertension
  7. Hypercalcaemia
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10
Q

What are the mechanisms of action of thiazide diuretics?

A
  1. Blocking Na+-Cl- cotransporter (probably by binding to the Cl- site)
  2. Small inhibitory effect on the action of carbonic anhydrase
  3. Causes vasodilation
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11
Q

What are the side effects of thiazide diuretics?

A
  1. Hypokalaemia and metabolic alkalosis via the same mechanisms as loop diuretics.
  2. Increased Mg2+ excretion but decreased Ca2+ excretion.
  3. Decreased excretion of uric acid, potentially causing gout.
  4. Impaired glucose tolerance, possibly as a result of altered KATP activity in the pancreatic islet cells.
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12
Q

Which part of the renal tubules do thiazide diuretics act on?

A

Cortical TAL and early DCT

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13
Q

What are the clinical uses of thiazide diuretics?

A
  1. Hypertension
  2. Mild cardiac failure
  3. Resistant oedema
  4. Nephrotic diabetes insipidus
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14
Q

What is the mechanism by which loop and thiazide diuretics cause hypokalaemia?

A
  1. In the DCT, Na+ is reabsorbed through ENaC down concentration gradient created by the Na+/K+-ATPase.
  2. This creates a lumen-negative potential that drives excretion of K+ through ROMK.
  3. Decreased absorption of Na+ due to loop and thiazide diuretics causes more Na+ to be delivered to DCT.
  4. More Na+ reabsorbed through ENaC and so greater lumen-negative potential created, driving more K+ secretion through ROMK.
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15
Q

What are the mechanisms of K+-sparing diuretics?

A
  1. Amiloride and triamterene block ENaC
  2. Spironolactone is an antagonist of aldosterone activity (which promotes K+-excretion in DCT by increasing expression of Na+/K+-ATPase and ROMK).
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16
Q

What is the product of spironolactone metabolism and its function?

A
  • Spironolactone is metabolised to canrenone in the liver.
  • Both itself and canrenone act as competitive inhibitors of aldosterone binding onto its cytoplasmic receptors.
17
Q

Which part of the renal tubules do K+-sparing diuretics act?

A

DCT

18
Q

What are the mechanisms of action of CA inhibitors?

A
  1. Inhibition of CA causes ↓ in luminal [H+] and decreases absoprtion of HCO3-, trapping Na+ in lumen as NaHCO3.
  2. This increases amount of secreted Na+ and thus amount of urine produced.
19
Q

What is a problem with effective dosages of CA inhibitors?

A

They need to be high as there needs to be 99% inhibition of CA to produce appreciable diuretic effects.

20
Q

What are the clinical uses for CA inhibitors?

A
  1. Glaucoma
  2. Altitude sickness
21
Q

Which part of the renal tubule do CA inhibitors act?

A

PCT

22
Q

What is the mechanism of action of osmotic diuretics?

A
  1. Molecules that are filtered in the glomerulus but not absorbed in the renal tubules (e.g. inulin, mannitol).
  2. They increase osmotic potential of filtrate and so decreases water reabsorption and consequently Na+ reabsorption in PCT due to decreased filtrate [Na+].
23
Q

Which part of the renal tubule do osmotic diuretics act?

A

Along whole length

24
Q

What is gout?

A

Arthritis caused by deposition of sodium urate crystals in the joints and th surrounding tissues. It is caused by excess levels of uric acid in blood.

25
Q

How is the release of renin stimulated?

A
  1. Intrarenal baroreceptors (walls of afferent arteriole): Decreased stretch.
  2. Renal sympathetic nerves: Reflex increase in sympathetic tone due to reduced MAP.
  3. Macula densa: Reduced delivery of Na+ to DCT due to reduced GFR.
26
Q

What is the mechanism of action of the RAAS?

A
  1. Renin is secreted from the juxtaglomerular apparatus in the kidneys in response to reduced MAP.
  2. Renin is an enzyme that cleaves angiotensinogen to ATI.
  3. ATI is cleaved to ATII via action of ACE (mainly in pulmonary circulation).
  4. ATII has numerous functions, one of which is to stimulate release of aldosterone from adrenal cortex.
  5. Aldosterone acts on the DCT to increase absorption of Na+ and secretion of K+.
27
Q

What are the main types of angiotensin II receptors?

A
  1. AT1
  2. AT2
28
Q

What are the main functions of AT1 receptors?

A

AT1 is the main receptor responsible for mediating cardiovascular and renal responses such as vasoconstriction and increased Na+ reabsorption.

29
Q

What are the main functions of AT2 receptors?

A

AT2 is mainly found in the brain and adrenal medulla and has number of functions not directly related to cardiovascular system:

  1. Vasodilation via NO and cGMP
  2. Inhibition of cellular proliferation, neuronal differentiation and apoptosis
30
Q

How is ATIII formed and what are its functions?

A
  • Formed from cleavage of ATII by brain aminopeptidase-A
  • Has the same effects as ATII through AT1 and AT2 receptors
31
Q

How is ATIV formed and what are its functions?

A
  • Formed from cleavage of ATII by aminopeptidase-N
  • Acts through AT4 receptors, which are transmembrane insulin-regulated membrane aminopeptidases (IRAPs) and may be involved with memory, learning and long-term potentiation
32
Q

Why do ACE inhibitors cause coughing?

A
  1. ACE in involved in breakdown of bradykinin to inactive metabolites.
  2. Inhibition of ACE causes increases in blood levels of bradykinins.
  3. This induces coughing (possibly via inflammatory process in airways).
33
Q

When is ANP released?

A

In response to increased RAP due to MSFP and thus MAP

34
Q

What is the overall effect of ANP?

A

Reduces MAP and TBV

35
Q

What are the mechanisms of action of ANP?

A
  1. Vasodilation
  2. Reduced release of NA and sympathetic vasoconstriction
  3. Inhibits Na+ reabsorption in CD and increases GFR to cause natriuresis
  4. Inhibits RAAS by inhibiting renin release

Mechanism of Drug Action (28 decks)

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