Autocrine Regulation of Prolactin Secretion by Prolactin Variants Released from Lactating Rat Adenohypophysis

Abstract

Background. Previous work hasshown that the in vitro released prolactin (PRL) from the anterior pituitary (AP) of lactating 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.Methods. In the present experiments, we sought to determine whether PRL variants, released in vitro from lactotrophs of lactating rats, non-suckled (NS) for 6h or suckled (S) for 15 min after NS, were electroeluted from SDS-PAGE, and then were divided into 6 fractions, would influence the in vitro release of PRL variants from lactotrophs of NS and S rat APs.Results. 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 released 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.Conclusions. These results indicate that in addition to hypothalamic influence, the release of PRL variants from the lactating rat AP is regulated also by autocrine influences exerted upon the gland by the previously released PRL variants.

Autocrine and Paracrine Regulation of Prolactin Secretion by Prolactin Variants and by Hypothalamic Hormones

“…Moreover, the present results confirm previous findings (Huerta-Ocampo, 2007;Mena et al, 2010;Mena et al, 2011;Möderscheim et al, 2007, Mena et al, 2012a, that CM from lactating rats, contain prolactin variants capable of inducing rapid release of PRL from the untreated male rat pituitary, and that they can also activate of astrocytes and neurons in different areas of the central and peripheral nervous system (Mena et al, 2012b …”

“…Also, as shown previously (Mena et al, 2010) our results obtained by Western blotting confirm that CM from lactating rat pituitary contains several prolactin variants, i.e., 37-46 kDa as well as 16-25 kDa, capable of stimulating PRL release from male rat pituitary. In addition, CM obtained from male rat pituitary regions as well as PRL standard have no significant stimulatory effect on PRL secretion of pituitary regions from either lactating or male rats (Huerta-Ocampo, 2007;Mena et al, 2010), this suggests that the male pituitary gland is deficient in the same PRL variants, and of other possible factors, that are released by the lactating rat AP, even though it does contain receptors for stimulating factors released from the anterior pituitary of lactating rats (Mena et al, 2011;Mena et al, 2012a).…”