IN-VITRO IMMUNONEUTRALIZATION OF A CLEAVED PROLACTIN VARIANT - EVIDENCE FOR A LOCAL PARACRINE ACTION OF CLEAVED PROLACTIN IN THE DEVELOPMENT OF GONADOTROPHS AND THYROTROPHS IN RAT PITUITARY

We have previously isolated a cleaved prolactin variant, secreted by r at pituitary cells in culture, that stimulated [H-3]thymidine incorpor ation into DNA in gonadotrophs and thyrotrophs when added to pituitary aggregate cell cultures of 14-day-old female rats. Using synthetic pe ptides homologous to the new C- and N-termini of the cleavage site, we made antisera recognizing this cleaved variant without significant cr ossreaction with native prolactin, Addition of these antisera to pitui tary aggregate cell cultures decreased [H-3]thymidine incorporation in to DNA in gonadotrophs and thyrotrophs but not in the other pituitary cell types. These data are further evidence that this prolactin varian t, cleaved between Tyr-145 and Leu-146, may have an important role as growth regulator of the gonadotrophs and thyrotrophs in the rat pituit ary.