Physiology of Pituitary hormones

Anterior Pituitary Hormones

1. Polypeptides/proteins – ACTH, prolactin, growth hormone


2. Glycoproteins – TSH, LH, FSH


3. Tropic hormones (ACTH, TSH, FSH, LH, GH) – stimulate secretion of hormonally active substances by other endocrine glands or in case of GH, the liver and other tissues.


4. A number of other peptides are synthesized and secreted from anterior pituitary together with ACTH: endogenous opiate beta endorphin, precursor of Melanocyte-stimulating hormone (Melanotropins).


5. Prolactin
a) Prolactin secretion may be influenced by PRH but is mainly controlled by PIH (probably dopamine).

b) During pregnancy, stimuli which reduce PIH release from hypothalamus raises prolactin levels- favouring development of breast ready for lactation and as part of suckling reflex during lactation.


6. Growth Hormone
Long arm of human chromosone 17 contains GH-hCS cluster genes:
a) hGH-N (normal)
b) hGH-V (variant)
c) hCS (2 codes)
d hCS pseudogene

Species specificty

7. Growth Hormone Receptor
Somatomedins – effects of GH on growth, cartilage and protein metabolism depend on interaction between GH and Somatomedins (peptide growth factors).


8. Actions of GH
a)Effects on growth -stimulates the growth of long bones, accelerated chondrogenesis, more matrix at the end of long bones, stature is maintained.

Abnormalities of GH may lead to gigantism.

When epiphyses are closed, GH produces pattern of bone & soft tissue deformity (Acromegaly)


b) Effects on protein & electrolyte metabolism
Produces positive nitrogen and phosphorus balance.

Fall in blood urea nitrogen and amino acid levels.

Increase in metabolic rate.

Fall in plasma cholesterol.

Gastrointestinal absorption of calcium is increased.

Sodium and potassium excretion is reduced.

Stimulates synthesis of soluble collagen.


c) Effects on carbohydrate & fat metabolism

Diabetogenic – increases hepatic glucose output and anti-insulin effect on muscle.

Ketogenic – increases circulating FFA levels.

Increases ability of pancreas to respond to insulinogenic stimuli such as arginine and glucose.


9. Regulation of GH

The secretion of GH undergoes marked and rapid spontaneous fluctuation in children and young adults before it declines in old age.

Hypothalamic control

a) Growth hormone-releasing hormone (GRH)
b) Growth hormone release-inhibiting factor (somatostatin)
c) ghrelin – has GH stimulating activity.