Multiple prolactin-releasing activity in the bovine hypothalamic extract

Area of Science:

• Endocrinology
• Neuroscience
• Biochemistry

Background:

• Prolactin (PRL) secretion is regulated by hypothalamic factors.
• Bovine hypothalamic extract (BHE) is known to possess prolactin-releasing activity (PRA).
• The precise nature of PRL-releasing substances in BHE remains to be fully elucidated.

Purpose of the Study:

• To compare the PRA of BHE with known PRL-releasing substances.
• To characterize the active components within BHE using chromatographic techniques.
• To identify novel PRL-releasing factors in bovine hypothalamus.

Main Methods:

• In vitro bioassay using cultured rat adenohypophysial cells to measure PRL secretion.
• Dose-response studies with BHE and known peptides: vasoactive intestinal peptide (VIP), thyrotropin-releasing hormone (TRH), and beta-endorphin (END).
• Gel filtration (Sephadex G-100) and two-step reversed-phase high-performance liquid chromatography (RP-HPLC) for purification and separation of active components.

Main Results:

• BHE demonstrated marked, dose-dependent stimulation of PRL secretion.
• VIP, TRH, and END showed significant PRA, but their dose-response slopes suggested they did not account for the major active elements in BHE.
• Gel filtration and RP-HPLC resolved BHE into multiple PRA peaks, distinct from known peptides, indicating the presence of unique PRL-releasing factors.

Conclusions:

• Bovine hypothalamic extract contains unique factors responsible for prolactin-releasing activity.
• These novel factors are distinct from previously characterized PRL-releasing peptides such as VIP and TRH.
• Further investigation is warranted to isolate and identify these unique bovine hypothalamic PRL-releasing peptides.