Renal Tubular Disease

Question 1

What’s the main function of the Loop of Henle?

Answer 1

to reabsorb Na+
- approx 30% of the filtered Na+ is reabsorbed
- generates the medullary gradient

Question 2

What’s the main function of the distal tubule and collecting tubule/duct?

Answer 2

• fine regulation of electrolytes (Na+, K+, Ca2+)
• acid/base regulation
• water resorption

Question 3

Define cystinuria.

Answer 3

Inheritable genetic defect leading to failure of particular non-essential amino acid reabsorption
- cystine is insoluble in acidic urine –> forms calculi

Question 4

What’s the clinical signs of cystinuria?

Answer 4

• calculi formation usually noted around 5y
• Lab and Newfies as young as 4-6m
• stranguria, pollakiuria, and hematuria
• urethral obstruction (male)

Question 5

What’s the treatment for cystinuria?

Answer 5

• protein restricted diet
• alkalinization of urine (usually done with diet, can be done with thiol drugs, like 2-MPG)

Question 6

What’s the significance of carnitinuria?

Answer 6

excessive loss will lead to deficiency –> cardiomyopathy

Question 7

How does carnitinuria happen and how is it treated?

Answer 7

Can occur with dogs with cystinuria, but a high fat diet would exacerbate carnitine loss

Question 8

What defect makes Dalmatian more prone to hyperuricosuria?

Answer 8

• defect in uric transport across the hepatic membrane –> limited uric metabolism
• also has less reabsorption in the proximal tubule
• a defective membrane transport –> active secretion in the distal tubule
• has normal uricase

Question 9

How common is hyperuricosuria in Dalmatians?

Answer 9

25% of male Dalmatians will show clinical signs
- autosomal recessive

Question 10

What’s another cause of hyperuricosuria, esp in non-Dalmatians/ cats?

Answer 10

primary liver disease

Question 11

How is hyperuricosuria treated in Dalmatians?

Answer 11

allopurinol

Question 12

What’s the MOA of allopurinol?

Answer 12

It’s a XO inhibitor –> blocs the metabolism of hypoxathine and xanthine to uric acid
- do NOT give allopurinol if not on purine restricted diet –> will lead to hyperxanthinuria

Question 13

How is liver-related hyperuricosuria treated?

Answer 13

NOT with allopurinol (also don’t give to cats)

Question 14

How is dilute urine accomplisehd?

Answer 14

protein restricted diet reduces renal medullary concentration ability

Question 15

What’s the max transport capacity for glucose in the proximal tubules?

Answer 15

Dogs: 10-12.2 mmol/L
Cats: 14.4-17.2 mmol/L

Question 16

Define Fanconi Syndrome.

Answer 16

• glucosuria with euglycemia
• also have amino acid in urine, and bicarbonate loss leading to systemic acidosis

Question 17

What are some causes of Fanconi Syndrome?

Answer 17

• Inherited: Basenji! 10-30% of them
• Acquired: toxins, hypoparathyroidism, cancer, gentamicin, toxins that cause proximal tubular necrosis

Question 18

What’s the MOA of Fanconi Syndrome?

Answer 18

• abnormal glucose absorption –> glucosuria –> osmotic diuresis
• amino acid resorptive abnormalities
• abnormal absorption of bicarbonate, Na+, K+ and urate

Question 19

What are some clinical signs of Fanconi Syndrome?

Answer 19

• PU/PD
• weight loss
• poor haircoat
• weakness
• dehydration
• weakness from hypokalemia

Question 20

What’s the treatment for Fanconi Syndrome?

Answer 20

Inherited = supportive therapy only
Acquired = resole underlying cause

Question 21

What’s the prognosis for Fanconi Syndrome?

Answer 21

with intensive supportive therapy = approx 5y

Question 22

How does the renal tubules maintain acid/base balance?

Answer 22

Proximal tubule: reabsorption of bicarbonate
Distal tubule: excretion of H+

Question 23

What’s the abnormalities noted with a proximal tubule renal tubular acidosis?

Answer 23

• hyperchloremic
• metabolic acidosis is self-limiting as the distal tubule can excrete H+
• acid urine pH
• normal GFR

Question 24

What’s the abnormalities noted with a distal tubule renal tubular acidosis?

Answer 24

• hyperchloremic
• metabolic acidosis, more severe than proximal tubule RTA

Question 25

What is nephrogenic diabetes insipidus?

Answer 25

Congenital (rare): deficiency of ADH receptors
Acquired: receptor interference - drugs, toxins (E coli), metabolic conditions (hypokalemia, hypercalcemia), tubular injury/ loss

Question 26

How is nephrogenic diabetes insipidus treated?

Answer 26

• Na+ and protein restricted diet –> less solutes to the kidneys, less urine produced
• diuretics! induce mild dehydration will promote proximal tubule water reabsorption –> reduces urine output by 20-50%