biochemstry of hormone

1. 1 .Hypothalamic Hormones
 At least seven hormones are secreted by the hypothalamus.
 They are involved with homeostatic mechanisms, their secretion is not constant,
rather they are released in bursts.
 Their secretion is under tight feedback control of;-
 the pituitary hormones or the hormones secreted by peripheral endocrine glands.
 Stimuli from the central nervous system also control the secretion of hypothalamic
hormones.
 Actions of the hypothalamic hormones on their target cells in the pituitary are
mediated by:

2. Cont......
a. calcium phosphoinositide system or
b.via the cAMP second messenger system.
1.1 Thyrotropin-releasing Hormone (TRH)
 it stimulates the synthesis and secretion of TSH.
 It binds to the cell surface receptors that are linked to phospholipase-C.
The resulting phosphoinositides stimulate the release of calcium from intracellular storage sites and
so lead to exocytosis of TSH.
The latter stimulates the synthesis and release of thyroid hormones (T3 and T4).

3. Cont......
1.2 Corticotropin-releasing Hormone (CRH)
 It acts via the cAMP second messenger system to stimulate the release of the pituitary ACTH.
The latter in turn acts on the adrenal cortex to stimulate the release of adrenocorticosteroids,
mainly cortisol.
1.3 Arginine Vasopressin (AVP)
 It elicits an inhibitory effect on the pituitary opposite to that of CRH,
• by altering the intracellular calcium-ion channels.
1.4 Gonadotropin-releasing Hormone (GnRH)
 it stimulates the synthesis and secretion of both FSH and LH.
 Its action is mediated via a calcium-phosphoinositide system.

4. Cont......
1.5 Growth Hormone-releasing Hormone (GHRH)
It binds to its receptor on the pituitary somatotroph cell.
It triggers both adenylate cyclase and the intracellular calcium- calmodulin system.
It stimulate GH transcription and release.
1.6 Growth Hormone Release-inhibiting Hormone (GHRIH)
GHRIH, also called somatostatin.
They inhibit GH secretion by lowering intracellular cAMP concentration.
 Inhibition of TSH secretion is also brought about by somatostatin.

5. Cont......
1.7 Prolactin Release-inhibiting Factor (PRIF)
Prolactin is unique among the pituitary hormones in that it is under predominant inhibitory control
from the hypothalamus.
 PRIH is a very simple molecule, dopamine, which works by inhibiting adenylate cyclase.
Dopamine inhibits both prolactin synthesis and secretion.
Some of these hypothalamic hormones are synthesized in other tissues also.
Somatostatin, for example, is found in the cells of the pancreas in higher concentrations than in the
hypothalamus,
 and it plays an important role in regulating the secretion of insulin and glucagon .

6. 2. Anterior Pituitary Hormones
The anterior pituitary or adenohypophysis is an endocrine target organ for hypothalamic hormones.
hypothalamic hormones reach the pituitary via the portal system and induce cause it to release its
hormones into the general circulation.
The hormones are secreted as either peptides (ACTH, GH, PRL, chorionic somatomammotropin)
or glycoproteins (TSH, LH, FSH).
Classification of Anterior Pituitary Hormones
 The anterior pituitary hormones have been divided into three broad groups:
1.The growth hormone-prolactin-chorionic somatomam-motropin group:
2.The glycoprotein hormones:
3. The pro-opiomelanocortin peptide family (POMC):

7. (GH) Cont......
2.1 Growth Hormone, (GH)
A single peptide made up of 191 amino acids.
Produced by somatotrophs under the control GHRH from the hypothalamus.
Plays an important role both at birth and at puberty .
 Coordinates normal growth and development.
Receptors that respond to GH exist on cells and tissues throughout the body.
The most pronounced effect of GH is on linear skeletal development, but GH also greatly
increases lean muscle mass.

8. (GH) Cont......
 Actions of Growth Hormone
• GH has many diverse effects on metabolism.
• It is considered an amphibolic hormone because it directly influences both anabolic and catabolic
processes.
• It enhance protein synthesis in skeletal muscle and other tissues, decreases protein catabolism
• GH directly antagonizes the effect of insulin on glucose metabolism,
• It promotes hepatic gluconeogenesis, and stimulates lipolysis.
– Effect on fats: it has a lipolytic effect: to give energy.
– Effect on CHO: It has diabetogenic effect.

9. (GH) Cont......
• Decrease glucose utilization, Increase glycogen deposition,
• Decrease number of insulin receptors, Decrease glucose uptake by the cells.
• GH also has indirect effects that are mediated by factors that were initially called somatomedins
• Causes the liver to form somatomedins that strongly increase all aspects of bone growth
- stimulation of osteoblasts, increased protein deposition by chondrocytic & osteogenic cells
• Effects of somatomedins on growth are similar to that of insulin
• So, it is called Insulin like growth factors( IGFs).
• It cause increase glucose & amino acids uptake by the cells.

10. (GH) Cont......