High affinity histamine H3 receptors regulate ACTH release by AtT-20 cells

Area of Science:

• Neuroendocrinology
• Pharmacology
• Cell Biology

Background:

• Histamine H3 receptors are primarily found in the central nervous system.
• Previous studies indicated the presence of H3 receptors in the pituitary gland.
• The AtT-20 cell line, derived from a murine anterior pituitary tumor, serves as a model for studying pituitary hormone regulation.

Purpose of the Study:

• To identify and characterize histamine H3 receptors on the AtT-20 cell line.
• To investigate the role of histamine H3 receptors in regulating adrenocorticotropic hormone (ACTH) release from AtT-20 cells.

Main Methods:

• Radioligand binding assays using [3H]N alpha-methylhistamine to quantify H3 receptor binding sites.
• Competition binding studies with selective H1, H2, and H3 receptor ligands to confirm receptor identity.
• Dose- and time-dependent experiments measuring ACTH release in response to H3 receptor agonists and antagonists.

Main Results:

• High-affinity histamine H3 receptors (KD = 0.7 nM) were identified on AtT-20 cells, with approximately 5000 sites per cell.
• The H3 receptor-specific agonist (R)-alpha-methylhistamine dose-dependently increased ACTH release.
• This increase in ACTH release was specifically blocked by the H3 antagonist thioperamide, confirming the involvement of H3 receptors.

Conclusions:

• The AtT-20 cell line expresses functional high-affinity histamine H3 receptors.
• Histamine H3 receptors play a regulatory role in controlling ACTH release from pituitary cells.
• This study provides the first cell line model for investigating H3 receptor function in the pituitary gland.