Characterization of lactogen binding sites in choroid plexus

Area of Science:

• Neuroscience
• Endocrinology
• Biochemistry

Background:

• Prolactin binding sites were previously identified in the rat choroid plexus.
• The specificity of these binding sites requires further characterization.

Purpose of the Study:

• To characterize the binding specificity of prolactin receptors in the rat choroid plexus.
• To investigate the presence and characteristics of prolactin binding sites in the brains of various species, particularly pigs.

Main Methods:

• In vivo radioautography using radiolabeled human growth hormone (125I-hGH) and ovine prolactin (125I-oPRL).
• In vitro binding assays with 125I-oPRL on choroid plexus from rat, rabbit, sheep, and pig.
• Detailed characterization of 125I-oPRL binding to pig choroid plexus, including protein concentration, temperature, time, pH, and cell fractionation.
• Competition assays using unlabeled lactogens and unrelated peptides.

Main Results:

• Intense radioautographic reaction in rat choroid plexus with 125I-hGH and 125I-oPRL, inhibited by unlabeled hGH and oPRL, but not by bovine growth hormone (bGH).
• Specific 125I-oPRL binding demonstrated in choroid plexus of multiple species, with the highest concentration found in the pig brain.
• Optimal binding conditions for pig choroid plexus identified (4°C, 30-40h incubation, pH 5.5-7.5), with binding sites enriched in microsomes.
• High-affinity binding of 125I-oPRL and 125I-hGH, with hGH and oPRL showing equipotent inhibition, while bGH and other peptides were non-inhibitory.

Conclusions:

• The choroid plexus contains specific, high-affinity binding sites for prolactin and human growth hormone.
• These binding sites exhibit characteristics consistent with lactogen receptors and are highly concentrated in the pig choroid plexus.
• The findings suggest a potential role for prolactin and growth hormone in the choroid plexus across species.