physiology of hypoadrenocoticism

Question 1

explain how low blood pressure is detected in the kidneys

Answer 1

• renin release stimulated by baroreceptors in the wal of the afferent arteriole
• cells of the macula densa in the early distal tubule which are stimulated by reduction in NaCl delivery

Question 2

give an overview of the RAAS system

Answer 2

Question 3

there are 3 classifications of hypoadrenocorticism. what are they? which ones are important?

Answer 3

1. primary hypoadrenocorticism (addisons disease) = loss of adrenal cortex
2. secondary hypoadrenocorticism (deficiency of ACTH) = rare
3. iatrogenic hypoadrenocorticism (from exogenous steroids)

primary = CR
iatrogenic occurs but usually due to overzealous tx of cushings or acute stop of steroid use

Question 4

what is addisons disease and what are the causes in dogs

Answer 4

• deficiency of glucocorticoids (cortisol) and mineralcorticoids (aldosterone)
• occurs with loss of 85-90% of adrenal cortex
• caused by idiopathic atrophy (probably immune mediated destruction) or iatrogenic (by drugs or surgery)

Question 5

briefly describe secondary hypoadrenocorticism

Answer 5

• rare deficiency of ACTH
• cortisol deficiency as result

Question 6

what is the signalment of cushings. name breeds which are predisposed

Answer 6

• young-middle aged dogs (median age = 4-6 years)
• 70% females
• any breed but certain predispositions
• extremely rare in cats

breeds:
- standard poodles
- bearded collies
- portuguese water dog
- leonberger
- great dane
- rottweiler
- WHWT and soft coated wheaten terriers

Question 7

what is the history and clinical signs of addisons

Answer 7

• usually nothing (pathognomonic)
• waxing and waning with non specific signs (chronic) worsened by stress
• if acute usually come in collapsed with marked hypovolaemia and azotaemia
• anorexia,
• vomiting,
• diarrhea,
• PU/PD
• weakness
• lethargy
• depression

Question 8

explain the pathophysiology of addisons if the deficiency is caused by aldosterone. glucocoticoid?

Answer 8

aldosterone
- loss of Na+, Cl- and H20
- retention of K and H
- pre renal failure (due to low circulation, not issue of kidney themselves)

glucocorticoid
- decreased stress tolerance
- GI signs
- weakness
- appetitie loss
- anaemia
- impaired gluconeogenesis

Question 9

name common clinical pathology seen in blood analysis in addisons

Answer 9

• lack of stress leukogram on CBC
• anemia (due to erythtocytosis due to lack of cortisol or GI blood loss)
• hyperkalaemia (high K)
• hyponatraemia (low Na)
• hypochloridaemia (low Cl)
• low Na:K ratio
• renal tubular resorption of Na and Cl
• excretion of K and H
• increased renal parameters (due to azotaemia)
• hypoglycemia
• low USG (inappropriately for dehydrated animal)

Question 10

how do you diagnose addisons

Answer 10

ACTCH stim test
cortisol levels wont change in diseased animal
- sensitive and specific if no prior steroid use (except dex as it doesnt interfere with assay)

Question 11

how do you treat addisons

Answer 11

• mineralcorticoids (desoxycortone pivalate) to replace aldosterone
• glucocorticoids during crisis or times of stress, not usually needed long term