L16a: Growth Hormone (GH) - Structure, Function & Dysfunction

what is another name for GH?

Somatotropin

what type of hormone is GH?

peptide hormone

Where is Growth Hormone produced?

The anterior pituitary gland.

What hypothalamic hormones regulate GH release?

GHRH (stimulates) and GHIH/somatostatin (inhibits).

Name stimuli that increase GH release.

1. Hypoglycemia/starvation

2. ghrelin (hunger hormone)

3. exercise/stress/trauma,sleep

4. n dogs progesterone during diestrus/pregnancy/contraception.

How is GH released over time?

In a pulsatile fashion with a background secretion and superimposed peaks.

When are GH levels highest?

During adolescence; they decline with age.

GH have what kind of metabolic effects?

direct metabolic effects via GH-receptors on target cells

What are IGFs and where are they produced?

Insulin-like growth factors;

• IGF-1 is produced in the liver and released into circulation

• IGFs 1–4 also act locally in tissues.

What is the role of IGF-1 in GH regulation?

elevated IGF-1 provides negative feedback on GH release.

List direct metabolic effects of GH.

Lipolysis and beta-oxidation of FFAs; gluconeogenesis; insulin resistance.

Describe GH action during low energy states.

Direct GH effects dominate

what processes are promoted by GH in low energy situations?

1. lipolysis

2. gluconeogensis

3. insulin resistance

Describe GH action during high energy states with adequate insulin.

IGF-1 is produced and IGF-mediated effects dominate, promoting protein anabolism.

in a great dane what would you expect IGF levels to be?

increased

What is acromegaly?

A condition of excessive GH production after puberty, leading to skeletal changes and possibly secondary diabetes mellitus.

what species have juvenile onset panhypopituitariism?

german sheperds

what are the effects of GH-IGF deficiency?

1. dwarfism

2. retained puppy coat

3. bilateral alopecia

4. delayted dentition

5. sterile

what hormone assays would you run for GH-IGH dysfunction?

1. IGF-1

2. GH

3. thyroid

4. cortisol

5. genetic testing

List common signs of feline acromegaly.

Joint problems, increased body weight, facial broadening, paw enlargement, prognathia with widened interdental spaces, laryngeal hypertrophy; possible organomegaly and secondary DM.

what causes acromegaly in cats?

functional pituitary tumors that secrete excess GH

what percentage of diabetic cats suffer from acromegaly?

25-30%

What causes GH excess in dogs during diestrus or with contraception?

Extended periods of high progesterone stimulating GH release from mammary glands.

Tx options for feline acromegaly.

1. Stereotactic radiation therapy

2. surgery

3. somatostatin analogs (GHIH),

4. insulin/DM management.

Which endocrine systems can be affected by GH-IGF axis dysfunction (deficiency)?

Thyroid (TSH), adrenal (ACTH), and reproductive (FSH/LH) c

What is hyposomatotropism?

Growth hormone deficiency (dwarfism).

Pituitary dwarfs are typically treated with what therapies?

Thyroid hormones and growth hormone replacement (e.g., porcine somatotropin).

What causes acromegaly in dogs?

Progestin exposure (diestrus or contraception) leading to GH release from mammary glands.