FSH isoforms: bio and immuno‐activities in post‐menopausal and normal menstruating women

OBJECTIVE The full expression of gonadotrophin biological activity depends on the gonadotrophin carbohydrate component. Our aim was to study serum FSH isoforms present in the follicular phase (FPS) and in the menopause (PMS) since the endocrine status may influence the structure of incorporated oligosaccharides. SUBJECTS Ten healthy post-menopausal women (age range 53–68) not receiving any hormonal treatment and 10 healthy women (age range 20–28) in the follicular phase of their menstrual cycle were studied. MEASUREMENTS Bio and immuno FSH-activities (Sertoli cell aromatase induction assay and RIA, respectively) were determined in separated isoforms after concanavalin A chromatography. Isolated isoforms were: UB, unbound; WB, weakly bound and FB, firmly bound to the lectin. RESULTS PMS showed two groups of immuno and bio-active FSH isoforms: WB, bearing biantennary galactosylated type and FB, bearing high mannose or hybrid type oligosaccharides. Immuno and bio-active FSH were not detected in the UB fractions. WB isoforms represented 82 ± 6% of the total bioactivity recovered in samples analysed individually; their B/I ratio was 0.85 ± 0.20. FB isoforms were 18 ± 6%; their B/I ratio was 3.27 ± 0.60. Whole serum B/I ratio was 1.20 ± 0.30. Similar results were obtained when pooled sera was analysed: WB: 77%, B/I: 0.82; FB: 23%, B/I: 3.75. Whole serum B/I in pooled samples was 1.10. FPS showed a different pattern. UB isoforms, bearing triantennary or bisecting oligosaccharides, were 41 ±3% of the total bioactivity recovered in samples analysed individually. Their B/I ratio was 0.61 ± 0.23. WB isoforms were 59 ± 3% and their B/I 0.76 ± 0.14. FB FSH isoforms were not detected. The whole serum B/I ratio was 0.60 ± 0.30. Similar results were obtained when pooled sera was analysed: WB 43%, B/I 0.42; FB 57%, B/I 0.62. Whole serum B/I in pooled samples was 0.70. CONCLUSIONS These results show that, in normal women, circulating FSH bioactivity is associated with isoforms with different oligosacharide structures according to hormonal status. FSH in the follicular phase has a higher degree of branching and a more complete carbohydrate chain than the FSH secreted during the menopause.