Pituitary hormones

Question 1

What is macroprolactin, why and how is it measured?*

Answer 1

Complex of prolactin & IgG that causes interpretive difficulties when present at Hi [ ]
When prolactin >700 mU/L, -> Precipitate macroprolactin with PEG and measure the prolactin on the supernatant.

Question 2

Detail some of the methodological issues in measurement of complex molecules using prolactin as an example. E.g. Lack of “harmonization” or standardization

Answer 2

• difficult to know what to use as gold std & difficult to find gold std for Hi MW
• in accuracies in assigning values to callibrators used by reagent & manufacturers

Question 3

Role of GH, ADH & Prolactin

Answer 3

GH: stimulate rowth and protein synthesis in all cells
ADH: inc permeability of CD to water (kidney)
Prolactin: stimulate mammary glands to produce milk

Question 4

How is GH regulated?

Answer 4

1. GH Releasing Hormone in hypothalamus
2. stimulates Ant. Pit. to secrete GH
3. Stimulates growth in cells & stimulate liver to release IGF (also stimulates growth)
4. IGH -ve FB on GHRH

Question 5

How do we investigate GH deficiency?

Answer 5

Conduct at least 2 provocative tests bc likely 1 test will fail

• Excercise GH stimulation test (measure GH at 0min, 2 min & 20 min)
• IV arganine over 30min, measure 60-120 min
• Insulin induced hypoglycemia: (*gold std)

Question 6

When can you use to measure IGF-I?

Answer 6

GH in excess NOT in DEFICIENCY

Question 7

investigation of excess GH

Answer 7

• Elevated IGF-1 (age related RR)

- Provocative testing w glucose tolerance test = target R to <5mU/L GH (hypergly. suppresses GH secretion)

Question 8

Assays used for measuring GH & IGF-1

Answer 8

GH: immunochemiluminometric assay: heterogenous & immunometric. but lack stdisation bw assays
IGF-1: Immunochemiluminometric assay. but lack lack stdisation bw assays, and lack data to make RR for age/gender

Question 9

Role of ADH (arginine vasopreessin)

Answer 9

Water balance in blood

• inc H2O absorption in DCT & CD in nephron
• inc vasoconstriction => inc aterial pressure

Question 10

Regulation of ADH (arginine vasopreessin)

Answer 10

• Regulated by osmoreceptors in hypothalamus (very sensitive to change in plasma osmolality
• Baroreceptors

Question 11

What is SIADH?

Answer 11

Syndrome of inappropriate ADH secretion

=> overload water absorbed = inc blood vol & hyponatremia = [ ]ed urine

Question 12

Tests conducted w diabetes insipidus

Answer 12

• water deprivation test: not eat or drink from 6pm to 7am. If urine osmolality is <850 mmol/Kg & plasma osmo if normal-high = imparied renal [ ]trating power. U/P ratio >3
• Pitressin stimulation test: injected w/ Synthetic ADH & sample 0min, 30-60min. <10% urine osmolality

Question 13

Stimulation of GH (4)

Answer 13

• Excercise
• Hypoglycemia
• Stress
• deep sleep

Question 14

Suppression of GH (5)

Answer 14

• Somatostatin (produced by stomach)
• IGF-1 (produced by stimulated cells)
• Hyperglycemia
• Obesity
• Hypothyroidism

Question 15

List causes of hypopituitarism ( failure to secrete 1 - all pit. hormones

Answer 15

• 1 or 2dary tumour: pituitary origin (damaged pit. stalk), or hypothalamic disease
• Infarction due to low blood circulation
• Iatrogenic: radio/chemo therapy

Question 16

How is Prolactin regulated?

Answer 16

regulated by inhibitory mechanism by PIF (dopamin)

Question 17

Stimulation of ADH (posterior ant. hormone)

Answer 17

nuerons in hypothalamus send signals to release ADH from post. anterior into portal circulation

Question 18

Cause of hyperprolactinaemia

Answer 18

• Physiological: Stress, suckling, preg, menopause
• Pathological: hypothalamic lesions, damage pit. stalk, hypothyroidism, chronic renal failure
• Macroprolactinaemia

Question 19

Ix of prolactinoma:

Answer 19

• Iatrogenic?stress/Hypothyroidism ruled out => do CT/MRI scan
• Check macroprotinaemia when [ ] is > 700mU/L

Question 20

Besides growth on cells, what are the other effects of GH to insulin in relation to

a) protein metabolism
b) glucose

Answer 20

a) promotes protein synthesis & transport of aa to cells (GH similar effects to insulin)
b) Hi glu = secretion of insulin & GH [IGNORE: opposite effects to insulin - cells not uptake glu = Hi glu = dec GH secretion (look like D.mellitus) ]

Question 21

What is IGF

Answer 21

Insulin like Growth Factor aka somatomedin

Question 22

causes of diabetes insipidus

Answer 22

• Hypothalamic disease by head injury, or pituitary tumour

- Chronic renal failure

Question 23

effect of pituitary stalk lesion to pituitary hormones

Answer 23

decrease except prolactin elevated

Question 24

How do labs screen for elevated prolactin

Answer 24

Precipitation of macroprolactin with PEG and measuring the prolactin on the supernatant.