The aims of this study were: (1) to examine whether the posterior pituitary contains prolactin releasing factor (PRF) activity, (2) to determine to what extent known neurohypophyseal peptides contribute to this activity, and (3) to compare posterior pituitary PRF activities of hens in different reproductive stages. Anterior pituitary cells derived from juvenile female turkeys were incubated with posterior pituitary extracts or test substances for 3 hr. Posterior pituitary extracts (0.1-0.8 equivalent) contained a potent substance(s) which stimulated PRL release in a concentration-dependent manner (2.4 ± 0.08 to 6.5 ± 0.23 μg/500 k cells). Arginine vasotocin (AVT) and vasoactive intestinal peptide (VIP) antisera (1:500) completely abolished the PRL-releasing activities of their respective peptides but partially reduced (P<0.05) the PRF activity of the posterior pituitary (AVT, 19.9%; VIP, 55.1%). Mesotocin antiserum did not alter (P>0.05) PRL release induced by posterior pituitary extract. Posterior pituitary cxtract (0.01-0.5 equivalent) from hens in each of the various stages of the reproductive cycle induced a concentration dependent PRL release. The 0.5 posterior pituitary equivalent dose from reproductively quiescent (nonphotostimulated), laying, photorefractory, and incubating hens increased PRL release 2.4-, 2.9-, 3.8-, and 11.1-fold, respectively. The turkey posterior pituitary contains a potent PRF activity, partially accounted for by VIP and AVT, at the assayed concentrations, which varies with the reproductive cycle.
Bibliographical noteFunding Information:
’ Minnesota Agricultural Experiment Station Scientific Journal Article. Research supported by USDA Grant 91-37203-6609 and NSF. 2 Send correspondence to M. E. El Halawani, 495 AnSci/VetMed Building, University of Minnesota, 1988 Fitch Avenue, St. Paul, MN 55108.