title: Rat milk inhibits the mitogenic response of Nb2 lymphoma cells to prolactin.
abstract: Prolactin-like bioactivity in the rat milk was observed using the lactogen specific Nb2 lymphoma assay. The water soluble fraction (infranatant) of pooled milk samples obtained on days 2, 12 or 22 postpartum stimulated Nb2 cell growth in the range of 0.08-2.5 microliters/well. Higher concentrations of day-12 and day-22 (but not day-2) milk infranatant, however, decreased Nb2 proliferation in a dose-dependent fashion. [3H]-thymidine incorporation used as an indicator of cell growth was decreased by 21%, 49% and 83% at the doses of 5, 10, 20 microliters/well concentrations of day-22 milk infranatant, respectively. Milk infranatant did not reduce cell viability as assessed by Erythrosin B exclusion test. Addition of exogenous rat PRL (NIH B-6) at concentrations of ED50-ED90 did not restore the Nb2 proliferation rate decreased by milk infranatant. Saturating doses of PRL (ED100-ED400) resulted in maximal cell growth, but failed to counteract the inhibitory effect of milk infranatant. The relative molecular weight of the putative Nb2 cell inhibitor of rat milk is between 10 kDa and 30 kDa as determined by ultrafiltration and dialysis. The inhibitory activity of milk infranatant is stable at physiological pH, but is destroyed upon acidification. Thirty min of incubation at 37 degrees C enhanced but 30 min of incubation at 100 degrees C only slightly decreased the calculated total inhibitory effect of milk infranatant. These initial results indicate the presence of a water-soluble antimitogenic factor in rat milk (rMAF) which inhibits the Nb2 lymphoma cell response to prolactin in a non-competitive manner.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802.
authors.forename: B E
authors.initials: BE
authors.lastname: Tóth
authors.forename: B
authors.initials: B
authors.lastname: Kacsóh
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamuro
authors.forename: L M
authors.initials: LM
authors.lastname: Avery
authors.forename: C E
authors.initials: CE
authors.lastname: Grosvenor
mesh_terms: D000818:Animals; D016923:Cell Death / Q000502:physiology; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D004273:DNA, Neoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D008223:Lymphoma / Q000378:metabolism / Q000473:pathology*; D008892:Milk / Q000502:physiology*; D008934:Mitogens / Q000494:pharmacology*; D011388:Prolactin / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
chemical_list: D004273:DNA, Neoplasm; D008934:Mitogens; D014316:Tritium; D011388:Prolactin; D013936:Thymidine