M. Lkhider et al., RAT PROLACTIN IN SERUM, MILK, AND MAMMARY TISSUE - CHARACTERIZATION AND INTRACELLULAR-LOCALIZATION, Endocrinology, 137(11), 1996, pp. 4969-4979
To study the localization of PRL in mammary epithelial cells (MEC) and
to characterize PRL forms in serum, milk, and mammary tissue, two gro
ups of lactating rats, a control group and a bromocriptine-treated gro
up, were compared. In serum and milk from control rats, two forms of P
RL (25 and 23 kDa) were detected by immunoblotting. In bromocriptine-t
reated rats, only the 25-kDa form was present. In mammary tissues from
control rats, 25-, 23-, and 14-kDa forms of the hormone were detectab
le, whereas only 25- and 14-kDa forms were present in bromocriptine-tr
eated rats. Immunofluorescence and immunogold electron microscopy reve
aled that in MEC from control rats, PRL was located in the organelles
involved in endocytosis and was also present in rough endoplasmic reti
culum, Golgi apparatus, secretory vesicles, and lumen of the acini. In
bromocriptine-treated rats, a decrease in the labeling was evidenced
in endosomes and multivesicular bodies. On the contrary, labeling asso
ciated with the rough endoplasmic reticulum and secretory vesicles was
increased. Thus, even when the amount of circulating PRL detected by
RIA was strongly decreased, PRL was always detectable in MEC and in th
e lumen of the acini, suggesting an active participation of MEC in the
transport of PRL to milk.