Hua G, George JW, Clark KL, et al. - Researchers investigated in vivo bioactivity of hypo-glycosylated human recombinant FSH (hFSH18/21) that drives follicle development in vivo in comparison with fully-glycosylated human recombinant FSH (hFSH24). In this cross-sectional study, the actions of purified recombinant human FSH glycoforms on parameters of follicular development, gene expression and cell signaling were evaluated in immature postnatal day (PND) 17 female CD-1 mice. They stimulated follicle development in vivo by treating PND 17 female CD-1 mice (n = 8–10/group) with PBS (150 µl), hFSH18/21 (1 µg/150 µl PBS) or hFSH24 (1 µg/150 µl PBS) by intraperitoneal injection (i.p.) twice daily (8:00 a.m. and 6:00 p.m.) for 2 days. Quantification of follicle numbers, serum anti-Müllerian hormone and estradiol levels, and follicle health was performed. In addition, they treated PND 17 female CD-1 mice acutely (2 h) in vivo with PBS, hFSH18/21 (1 µg) or hFSH24 (1 µg) (n = 3–4/group). Relative to fully-glycosylated hFSH, greater bioactivity was recorded for hypo-glycosylated hFSH, that enabled greater follicular health and growth in vivo, with increased transcriptional activity, greater activation of receptor tyrosine kinases and raised phosphatidylinositol 3-kinase/protein kinase B and Mitogen-activated protein kinase/extracellular signal-regulated kinase signaling.