For example, the binding of epinephrine to a β adrenergic-receptor subtype activates (through a stimulatory G protein) the enzyme, adenylyl cyclase. Adenylyl cyclase catalyzes the conversion of adenosine triphosphate (ATP) to the second messenger, 3', and 5'-cAMP.
Peptide or protein hormones, such as insulin, pituitary, hypothalamic, and parathyroid, are water soluble and circulate in free (unbound) forms. When insulin binds its receptors on muscle cells, an increase in glucose uptake by the muscle cells is the result.
ADH was originally named vasopressin because, in extremely high doses, it causes vasoconstriction and a resulting increase in arterial blood pressure. However, significant vasoconstriction may only be achieved pharmacologically.
Several different mechanisms, one of which is neural control (e.g., stress-induced release of catecholamines from the adrenal medulla), ...
Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates TSH secretion from the anterior pituitary. Secretion of TSH stimulates the synthesis and secretion of THs. Increasing levels of T4 and triiodothyronine (T3) then generate negative feedback on the pituitary and hypothalamus to inhibit TRH and TSH synthesis. ...
Releasing and inhibitory hormones are synthesized in the hypothalamus and are secreted into the portal blood vessels through which they travel to the anterior pituitary hormones.
ADH and oxytocin are synthesized in hypothalamic neurons but are stored and secreted by the posterior pituitary.