Activation of Prolactin Releasing Activity of Pregnant Rat Hypothalamic Extract by Enzymatic Digestion

Purification of rat prolactin releasing factor by gel filtration.

“…The fact that the prolactin releasing response to PRF was relatively close in prolactin response to suckling stimulation implies a possibility that PRF may physiologically regulate the secretion of prolactin in lactation. Lactating rats, as compared with nonlactating ones, maintain high prolactin levels in the blood for not less than one week (Takahashi et al 1976b), and a similar phenomenon is observed in man, too (del Pozo et al 1975). However, suckling stimulation alone cannot explain the high prolactin levels.…”

“…Although it is common to investigate activities in all fractions of the effluents from Sephadex and other ion exchange resin columns, in the present study biologic activities were examined for only the fractions showing the distinct absorptions by peptides, since it had already been shown that the PRF prepared from rat would most probably be a relatively low molecular polypeptide by Takahashi et al (1976b) Eventually, this method proved adequate, demonstrating the presence of PRF in fraction P2 with molecular weight of less than 3,000, and also proving the PRF to be a polypeptide. It has already been proved in a study using the bovine material that PRF is a polypeptide (Dular et al 1974) .…”