Prolactin (PRL) receptor gene expression in mouse adipose tissue: Increases during lactation and in PRL-transgenic mice

There are indications that PRL may exert important metabolic actions on adi pose tissue in different species. However, with the exception of birds, the receptor has not been identified in white adipose tissue. The present stud y was designed to examine the possible expression and regulation of the PRL receptor (PRLR) in mouse adipose tissue. The long PRLR messenger RNA (mRNA ) splice form (L-PRLR) and two short splice forms (S2- and S3-PRLR) were de tected in mouse adipose tissue by RT-PCR. Furthermore, L-PRLR mRNA was dete cted by ribonuclease protection assay. Immunoreactive PRLR with a relative molecular mass of 95,000 was revealed by immunoblotting. Furthermore, L-PRL R mRNA expression was demonstrated in primary isolated adipocytes. In mouse adipose tissue, the level of L-PRLR mRNA expression increased 2.3-fold dur ing lactation compared with those in virgin and pregnant mice. In contrast, in the liver the expression of L-PRLR increased 3.4-fold during pregnancy compared with those in virgin and lactating mice. When comparing the levels of L-PRLR expression in virgin female and male mice, no difference was det ected in adipose tissue. However, in virgin female liver the expression was 4.5-fold higher than that in male liver. As PRL up-regulates its own recep tor in some tissues, we analyzed L-PRLR expression in PRL-transgenic female and male mice. In PRL-transgenic mice L-PRLR expression was significantly increased in both adipose tissue (1.4-fold in females and 2.4-fold in males ) and liver (1.9-fold in females and 2.7-fold in males) compared with that in control mice. Furthermore, in female PRL-transgenic mice retroperitoneal adipose tissue was decreased in weight compared with that in control mice. However, no difference was detected when comparing the masses of parametri al adipose tissue. Our results suggest a direct role for PRL, mediated by P RLR, in modulating physiological events in adipose tissue.