Prolactin levels and molecular heterogeneity in rat strains with high and low incidence of DMBA-induced mammary tumors.

We compared the following parameters in Long-Evans (LE) and Sprague-Dawley (SD) female rats: 1) mammary tumor incidence after DMBA, 2) plasma prolactin (PRL) during the estrous cycle before and after DMBA, 3) plasma PRL in immature females from 0900 hr on day 29 to 0900 hr on day 30, 4) plasma PRL from 1200 to 1700 hr and before and 10 min after i.p. TRH administration in ovariectomized (OVX) rats treated with 200 micrograms polyestradiol phosphate (PEP), 5) anterior pituitary (AP) PRL concentration in OVX rats treated with 200 micrograms PEP, and 6) levels and Sephadex G-100 gel filtration patterns of plasma PRL 10 min after i.p. TRH administration in OVX rats treated with 200 micrograms PEP. We observed marked mammary tumor incidence in SD rats from one supplier (S-SD, Spartan) (96%) compared to SD from another supplier (CR-SD, Charles River) (40%) or LE rats (10%). Plasma PRL was significantly decreased on metestrus-diestrus and increased on proestrus-estrus in SD (both suppliers) but not in LE rats 90 days after DMBA compared to rats not given DMBA and sacrificed at same stages of the estrous cycle on day 55 of age. Immature LE and SD-CR females exhibited significant late afternoon and early morning prolactin surges on days 29-30 whereas SD-H rats had either no surges or poorly synchronized surges at the same times.(ABSTRACT TRUNCATED AT 250 WORDS)