Proposed mechanism of action of recombinant bovine somatotropin (rBST). This hormone has direct effects on basal metabolic rate and breast parenchyma; the effects on the MEC (blue arrow) are mediated by rBST/ST-R complex, which stimulates JAK2/STAT5 pathway and by IGF-1R/IGF-1 which promotes and upregulates IRS/PI3K/(AKT/PKB)/mTOR and Ras/Raf/(MAPK/ERK) pathways. This will induce cell proliferation and survival and increase milk protein synthesis in MEC.
