Related Experiment Video
Updated: May 5, 2026

Isolation of Peritoneum-derived Mast Cells and Their Functional Characterization with Ca2+-imaging and Degranulation Assays
Published on: July 4, 2018
Inhibitory action of a met-enkephalin on ACTH release in man
Abstract:
In order to study the mechanism of action of a Met-enkephalin (FK 33824) on the pituitary-adrenal axis eight normal male volunteers were subjected to an ACTH stimulation test. Lysine-vasopressing (LVP), 5 IU, was injected intramuscularly after pretreatment with 0.5 mg FK 33824 i.m. or a placebo. In six of the subjects the opiate was again administered preceding a single injection of 0.25 mg ACTH beta 1-24 i.m. Blood was collected at regular intervals and ACTH and cortisol concentrations analyzed in all samples. LVP induced significant plasma ACTH (P < 0.05) and cortisol (P < 0.001) increases. Pretreatment with FK 33824 completely antagonized the effect of LVP. Furthermore, the cortisol elevation after exogenous ACTH was not modified by previous administration of FK 33824. It is concluded that the Met-enkephalin derivative FK 33824 directly suppresses ACTH release from the pituitary without influencing adrenal synthesis of cortisol.
Related Concept Videos
GPCRs Regulate Adenylyl Cylase Activity
Indirect-Acting Cholinergic Agonists: Mechanism of Action
Reversible inhibitors like edrophonium bind to a specific part of the enzyme called the anionic catalytic site. They form noncovalent bonds, which means they are not strongly attached to the enzyme. This creates a temporary and less stable enzyme–inhibitor complex,...
Indirect-Acting Cholinergic Agonists: Pharmacological Actions
At the neuromuscular junction, these agents work by inhibiting the breakdown of acetylcholine, allowing it to remain bound to the receptor and bind to nearby receptors. This process leads to repetitive firing of the endplate, causing muscle...
Adrenergic Agonists: Indirect-Acting Agents
One mechanism involves depleting stored catecholamines by displacing them from synaptic vesicles. These agents, known as "displacers," are transported into vesicles at the expense of noradrenaline. Examples include amphetamine and tyramine, which lack a catechol moiety, resulting in prolonged action, improved oral...
Drugs Affecting Neurotransmitter Release or Uptake
Cushing Syndrome II: Pathophysiology

