Purification of rat prolactin releasing factor by gel filtration.

Pregnant rat hypothalamic fragments were extracted with 30 mM Tris-HCl buffer at pH 7.8, subjected to enzymatic digestion, and applied to gel filtration on Sephadex G-25 for purification of the prolactin releasing factor. Effect of the eluted fractions on the release of prolactin were tested by the determination of serum and pituitary prolactin after the injection in lactating rats. Prolactin was estimated by radioimmunoassay. One fraction (tube number 61--73) eluted later than synthetic ACTH enhanced release of prolactin 30 min after injection, but other fractions had no effect on the release of prolactin. Prolactin releasing factor would be quantitatively predominant over prolactin inhibiting factor in pregnant rat.