The hormone, ACTH, stimulates the adrenal gland to secrete large amounts of cortisol into the bloodstream. This action causes a euphoric response in the brain as well as a potent anti-inflammatory effect at the tissue level.
Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It is an important component of the hypothalamic pituitary adrenal axis and is often produced in response to biological. Its principal effects are increased production and release of corticosteroids.
ACTH stimulates secretion of the glucocorticoid steroid hormones from the adrenal cortex cells, especially in the zona fasciculata of adrenal glands. ACTH acts by binding to cell surface ACTH receptors, which are located primarily on the adrenocortical cells of the adrenal cortex. The ACTH receptor is a seven membrane-spanning G protein- coupled receptor. Upon ligand binding, the receptor undergoes conformation changes to stimulate the enzyme adenylyl cyclase, which does lead to an increase in intracellular cAMP and subsequent activation of protein kinase.
ACTH influences steroid hormone secretion by both rapid short term mechanisms that take place within minutes and slower long term actions. The rapid actions of ACTH include stimulation of cholesterol delivery to the mitochondria where the P450scc enzyme is located. P450scc catalyzes the first step of steroidogenesis and is cleavage of the side chain of cholesterol. ACTH also stimulates lipoprotein uptake into the cortical cells. This increases the bioavailability of cholesterol in cells of the adrenal cortex.
The long term actions of ACTH include stimulation of the transcription of the genes coding for steroidogenic enzymes, especially the P450scc, the steroid 11?-hydroxylase along with their associated electron transfer proteins. The effect is observed over several hours.
In addition to steroidogenic enzymes, ACTH also enhances transcription of the mitochondrial genes that encode for subunits of mitochondrial oxidative phosphorylation systems. These actions may actually be necessary to supply the enhanced energy needs of adrenocortical cells stimulated by ACTH.
Dosage and Administration: Adult Horses: The recommended dosage is 2.5 to 5.0 ml 4-6 hrs prior to the event given by intramuscular .
Storage: Store below 3 degrees C (REFRIGERATE), do not freeze and protect from light.