66 - Pituitary Hormones

somatotrophs

What secretes growth hormone (somatotropin)?

single chain polypeptide

How can we describe the growth hormone (somatotropin)?

fish & mammals

GH secretion is pulsatile and in a circadian patter in in what species?

humans, rodents, & fish

There is sexual dimorphism in GH secretion in what species?

males

There are large nocturnal pulses of GH in what sex (humans, rodents, and fish)?

females

There are more sustained secretion of GH in what sex (humans, rodents, and fish)?

growth spurt

What occurs at puberty, related to the growth hormone?

age

Does GH decreases with what factor?

1. GHRH

2. Decreased glucose

3. Decreased FFA

4. Increased AA (ex: arginine)

5. Hypoglycemia/fasting/starvation

6. Puberty (estrogen/testosterone)

What are the 6 stimulators of GH?

1. Somatostatin

2. Increased glucose, FFA

3. GH

4. Obesity

5. Somatomedins (IGFs)

What are the 5 inhibitors of GH?

GH

The following are actions of what?

-Metabolic actions on liver, muscle, adipose, bone

-Affects linear growth, protein synthesis, organ growth, carbohydrate and lipid metabolism

-Direct anabolic actions → Increased Ca absorption from gut, P reabsorption from kidney, protein synthesis in liver

-Indirect anabolic actions via somatomedins (insulin-like growth factors - IGF)

direct anabolic actions

What actions are associated with GH increasing Ca absorption from the gut, P reabsorption from the kidney, and protein synthesis in the liver?

indirect anabolic actions

What actions are associated with somatomedins (insulin-like growth factors - IGF)?

IGF-1

What is associated with somatomedin C?

IGF-2

What is associated with somatomedin A?

1. increased lean muscle mass

2. linear bone growth

3. organ size/function

What are 3 factors/events associated with indirect anabolic actions of GH?

IGF-1

Which insulin-like growth factor is associated with cartilage and bone growth, as well as protein synthesis and growth of muscle and other organs?

1. increased gluconeogenesis in the liver

2. increase lipolysis in adipose tissue

What are the 2 direct catabolic effects of GH?

maintain blood glucose within normal range

What does increased gluconeogenesis do in the liver?

causes temporary insulin resistance

How does decreased glucose uptake in muscle affect insulin?

1. Release of FFA into blood

2. Increased formation of ketones

What 2 things does an increase in lipolysis in adipose tissue achieve?

growth hormone

What causes lipolysis and release of fatty acids in adipose tissue and decreased glucose utilization in most tissues?

dwarfism

What does a deficiency of GH cause?

acromegaly

What does excessive GH secretion cause?

pituitary tumor

In cats, what can excessive GH secretion cause?

increased progesterone

During diestrus in dogs, excessive GH secretion causes what?

diabetic ketoacidosis

Increased growth hormone can lead to insulin resistance, ultimately leading to what?

antidiuretic hormone (ADH; vasopressin/arginine vasopressin)

Which posterior pituitary hormone is associated with the following?

-Synthesized primarily by neurons in supraoptic nuclei of hypothalamus

-Peptide precursor = prepropressophysin

prepropressophysin

What is the peptide precursor for antidiuretic hormone?

neurons in supraoptic nuclei of hypothalamus

Where is antidiuretic hormone primarily synthesized?

oxytocin

The following are associated with what posterior pituitary hormone?

-Synthesized primarily by neurons in paraventricular nuclei of hypothalamus

-Peptide precursor = prepro-oxyphysin

prepro-oxyphysin

What is the peptide precursor of oxytocin?

neurons inparaventricular nuclei of hypothalamus

Where is oxytocin primarily synthesized?

cell body in hypothalamus

The secretion of vesicles in the posterior pituitary is associated with action potentials from where?

suckling

What is the major stimulus for stimulation of oxytocin secretion?

milk let-down

What does suckling result in?

sensory receptors on myoepithelial cells of alveoli in mammary gland

Stimulation of oxytocin secretion is associated with what receptors and where are they located?

uterine contractions

What does stimulation of the cervix by a fetus result in?

smooth muscle

What muscle does oxytocin act on in the uterus?

sperm movement and ejaculation

Oxytocin also acts on tests, epididymis, and prostate to aid in what?

1. Increased plasma osmolarity

2. Decreased blood volume (hypovolemia)

3. Decreased blood pressure

4. Pain

5. Nausea

6. Hypoglycemia

7. Nicotine, opiates

What are the 7 stimulators of ADH secretion?

1. Decreased plasma osmolarity

2. Increased blood volume (hypervolemia)

3. Increased blood pressure

4. Ethanol

5. Glucocorticoids

What are the 5 inhibitors of ADH secretion?

reabsorb water

What do stimulators of ADH secretion do?

excreted in urine

Since inhibitors of ADH secretion dont reabsorb water, where do they end up?

ADH

Under what influence can water be reabsorbed into the blood, associated with the distal convoluted tubule and collecting duct being permeable to water?

ADH

Kidney and vascular smooth muscle are associated with actions of what?

kidney

What structure is associated with free water absorption?

ADH -> free water reabsorption

What is responsible for increasing water permeability of principle cells in the distal convoluted tubules and collecting ducts of the kidney?

V2

The ADH receptor is equivalent to what receptor?

principal cells

Aquaporin 2 is inserted into the membrane of what cells?

V1

Vascular smooth muscle contraction is associated with what receptor?

arterioles

Vascular smooth muscle contraction is associated with constricting what?

central diabetes insipidus

What condition is associated with lack of ADH secretion?

peripheral or nephrogenic diabetes insipidus

What condition is associated with the posterior pituitary being normal, but the principal cells in collecting duct being unresponsive to ADH?

syndrome of inappropriate ADH secretion

The following are associated with what condition?

-Excess ADH released from posterior pituitary (Ex: disorders in brain, certain medications)

-Hypervolemia and hyponatremia

-Urine very concentrated

syndrome of inappropriate ADH secretion

Urine is very concentrated in what condition?