Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)P>Background FSH is synthesized and secreted in multiple glycosylation variants with different oligosaccharide structures; the endocrine milieu regulates the composition of FSH carbohydrate moiety. Objectives To characterize serum FSH isoforms according to their sialic acid content and oligosaccharide complexity in regularly menstruating women and in depot medroxyprogesterone acetate (DMPA) users during the menopausal transition. Subjects and methods Ten regularly menstruating perimenopausal women aged 45-52, with mid-follicular phase FSH levels < 10 IU/l and 10 regularly menstruating women, aged 20-39, were included. Blood samples were collected on the ninth day of the menstrual cycle. Twenty DMPA users were divided into two groups (n = 10) according to age: DMPA(1), age range 20-39 and DMPA(2), age range 45-52. Blood samples were collected 90 +/- 5 days after the last injection of DMPA. Oestradiol (E-2), inhibin B (Inh B), Pro-alpha C levels and the relative abundance of FSH isoforms on the basis of charge (preparative isoelectric focusing) and carbohydrate complexity (Concanavalin A chromatography) were determined. Results Decreased Inh B and moderately elevated E-2 levels were observed in perimenopausal women associated with an increase in FSH sialylation and a decrease in its oligosaccharide complexity. DMPA induced changes in the hormonal profile and FSH molecular microheterogeneity; the secreted hormone was more heterogeneous and its oligosaccharides were less complex under this condition. Conclusion Serum FSH glycoforms with increased sialylation and decreased oligosaccharide complexity reflect the decline of the gonadal activity induced either by age or by the use of a DMPA as a contraceptive.714558565Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Consejo Nacional de Investigaciones Cientificas y TecnicasCONICET, ArgentinaFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [03/08391-7]