Late gestational exposure to flutamide alters stromal composition and immune landscape in the rat mammary gland during pre-puberty, peri-puberty, and adulthood.

Perinatal development of the mammary gland is regulated by hormonal signals that influence cell proliferation, extracellular matrix remodeling, immune cell recruitment, and intracellular signaling. Although the role of estrogen in mammary gland development is well established, the impact of androgens remains less understood. To address this gap, we inhibited androgen signaling in utero using the anti-androgen flutamide (FLU) and investigated the effects on mammary gland development in rats. Using an integrative strategy combining histology, transcriptomics, lipidomics, cytokine profiling, and high-resolution imaging, mammary tissue were analyzed at pre-puberty (postnatal days [PND] 21), peri-puberty (PND46), and adulthood (PND90). FLU exposure induced subtle, yet significant, alterations in mammary morphology and molecular signatures. At PND21, the FLU-exposed group exhibited an increased number of adipocytes with reduced size. Transcriptomic analysis revealed differentially expressed genes at PND21 and enrichment in pathways related to androgen response and immune signaling, but minimal changes at later developmental stages. Lipidomic profiling showed transient disruption in long-chain fatty acid composition at early developmental stages. Cytokine profiling revealed a reduced adaptive immune response at PND46 and PND90, and second-harmonic generation imaging demonstrated changes in collagen fiber orientation and density across all developmental stages. These data indicate that prenatal androgen signaling is essential for proper stromal development and the establishment of early transcriptional networks in the mammary gland, with only minor long-term effects on glandular architecture in adult nulliparous females.