PRELIMINARY CHARACTERIZATION OF BOVINE PINEAL PROLACTIN RELEASING (PPRF) AND RELEASE-INHIBITING FACTOR (PPIF) ACTIVITY

Bovine pineal glands were subjected to extraction with dilute acetic acid, gel filtration on Sephadex G-25 and subsequent ultrafiltration through Diaflo membranes PM10, UM2 and UM05. Various fractions derived at each step were tested for the presence of substances which stimulate or inhibit prolactin secretion in vitro and in vivo. Both prolactin releasing (PPRF) and release-inhibiting (PPIF) activities were observed. PPRF activity was present in certain fractions derived from Sephadex G-25 and in the PM10 residue (MW≃<10,000). Whereas both the UM2 residue (MW>1000) and UM05 filtrates (MW<500) was seen to inhibit pituitary prolactin release in vitro, the UM05 residue (MW>500 and <1000) inhibited prolactin release in vivo, possibly by stimulating the secretion of the hypothalamic prolactin inhibiting factor. On the basis of its inactivation by trypsin it was concluded that PPIF may be a peptide or contain a peptide moiety indispensible for its biological activity. Experiments are in progress to characterize pineal prolactin-regulating activities and to elucidate further the physiological role of the pineal gland in the regulation of prolactin secretion. © 1979 Springer-Verlag.