Influence of endogenous and exogenous sex hormones on plasma brain-derived neurotrophic factor

BACKGROUND: Brain-derived neurotrophic factor (BDNF) is a mediator of neuronal plasticity and influences learning, memory and cognitive behaviour. The aim of this study is to assess plasma BDNF variations according to hormonal status. METHODS: A total of 60 subjects were included: 20 fertile ovulatory women, 15 amenorrhoeic women and 25 postmenopausal women. Blood samples were collected after overnight fasting. For 5 out of the 20 fertile women, samples were collected every 2 days throughout the whole menstrual cycle. Following basal evaluation, 10 out of 25 postmenopausal women were administered a hormone replacement therapy (HRT) and reevaluated after 6 months of treatment. Plasma BDNF concentrations were measured by enzyme-linked immunosorbent assay. In fertile women, estradiol (E2), progesterone and gonadotrophins were also assessed. RESULTS: In fertile women, luteal phase levels of plasma BDNF were significantly higher than follicular phase levels ( P< 0.001). BDNF increased from early follicular phase up to Day 14 of the cycle, reaching a pre-ovulatory peak, similar to E2. A second rise took place during mid-luteal phase, with a peak on Day 24. Amenorrhoeic subjects, as well as postmenopausal women, showed significantly lower plasma BDNF levels compared with fertile females ( P< 0.001). BDNF was positively correlated with E2 and progesterone and negatively correlated with menopausal age. HRT restored BDNF levels to those present in fertile women during the follicular phase. CONCLUSIONS: Plasma BDNF levels are influenced by hormonal status. Modifications in BDNF circulating levels during the menstrual cycle suggest a potential role for gonadal sex hormones (E2 and progesterone) in regulating neurotrophin expression.