Changes in reproductive function and white blood cell proliferation induced in mice by injection of a prolactin-expressing plasmid into muscle

Prolactin (PRL) is a pituitary hormone involved in various physiological processes, including lactation, mammary development, and immune function. To further investigate the in vivo and comparative endocrine roles of PRL, mouse PRL cDNA fused to the cytomegalovirus promoter, was introduced into muscle by direct injection. Previously we studied the function of rat PRL using the same protocol. PRL mRNA was detected in the muscle following injection by RT-PCR and subsequent Southern blot analysis. PRL was also detected and Western blot analysis revealed a relatively high level of serum PRL. In the pCMV-mPRL-injected female mice, the estrous cycle was extended, especially in diestrus stage and the uterus thickening that was shown in normal estrous stage was not observed. In the pCMV-mPRL-injected male mice, new blood vessels were first found at 5 weeks of age and fully developed blood vessels were found after 8 weeks in the testis. The number of Leydig cells increased within the testis and the testosterone level in serum was observed high. Finally, the number of white blood cells (WBCs) increased in the pCMV-mPRL-injected mice. The augmentation of WBCs persisted for at least 20 days after injection. When injection was combined with adrenalectomy, there was an even greater increase in number of WBCs, especially lymphocytes. This increase was returned normal by treatment with dexamethansone. Taken together, our data reveal that intramuscularly expressed mouse PRL influences reproductive functions in female, induces formation of new blood vessels in the testis, and augments WBC numbers. Of notice is that the Leydig cell proliferation with increased testosterone was conspicuously observed in the pCMV-mPRL-injected mice. These results also suggest subtle difference in function of PRL between mouse and rat species.