ACTA ENDOCRINOLOGICA (BUC)

Background. Previous work has shown that the in vitro released prolactin (PRL) from the anterior pituitary (AP) of\r\nlactating rats, contains PRL variants i.e., from 7-14 to 70-97 kDa that when incubated with AP lactotrophs of male rats, and of rats in other conditions, they promoted the selective stimulation and/or inhibition of the in vitro release of PRL variants from APs of male rats and of rats in other conditions.\r\nMethods. In the present experiments, we sought to determine whether PRL variants, released in vitro from lactotrophs of\r\nlactating rats, non-suckled (NS) for 6h or suckled (S) for 15 min after NS, were electroeluted from SDS-PAGE, and then\r\nwere divided into 6 fractions, would influence the in vitro release of PRL variants from lactotrophs of NS and S rat APs.\r\nResults. The results obtained showed that, under non-reducing conditions, the fractions contained PRL variants of 7-23 to 97 kDa, and between 1 and more than 20 ng/μl of PRL protein. Thus similar amounts of total PRL (about 60 ng/μl), were released from each AP region of NS and S rats, except for the higher amount of PRL (80 ng/μl) released from the central AP region of NS rats. The effects of PRL variants\r\nreleased from lactotrophs of NS and S rat APs i.e., of stimulatory and/or inhibitory type were exerted upon the release of PRL variants, and of total PRL.\r\nConclusions. These results indicate that in addition to hypothalamic influence, the release of PRL variants from the\r\nlactating rat AP is regulated also by autocrine influences exerted upon the gland by the previously released PRL variants.