A tropin or tropic hormone is the one which influences the activities of the other endocrine gland. Principally those involved in stress and reproduction. These are carried by the blood to the other target gland.
The pituitary tropins are under the positive & negative control of peptide factors from hypothalamus
- It is secreted as a large precursor molecule, known as Pro-opio-Melanocortin (POMC), with a molecular weight of 32 kD.
- It is cleaved to give about 30 different endorphins & several hormones.
- The active adrenocorticotropic hormone (ACTH) is a polypeptide with 39 amino acids.
- The secretion of POMC is under the control of CRH.
- It is a stress hormone which is released from the pituitary in a pulsatile manner with a definite diurnal rhythm
- Its secretion is highest in the early morning and minimum at midnight
- Factors that increase ACTH secretion include Stress such as pain, cold exposure, acute hypoglycemia, trauma, depression, and surgery
- It binds to specific receptors on the adrenal gland
- Activates Adenylate cyclase which activates cAMP. The cAMP level is raised
- ACTH induces adrenocortical steroidogenesis through the melanocortin-2 receptor
- Steroid hormones in turn cause feedback inhibition of HPA (hypothalamopituitary adrenal axis)
- ACTH secreting tumors of pituitary will cause Cushing’s disease
- Deficiency of ACTH secretion may occur as a part of Panhypopituitarism
Metabolic role of ACTH
- The principal actions of corticotropin are exerted on the adrenal cortex and extra-adrenal tissue
- It Increases the synthesis of
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