Endocrine modulation of cortical and retinal baseline perfusion across the menstrual cycle

The ovarian hormones, oestrogen and progesterone, have vaso- and neuroprotective effects, potentially due to cerebrovascular interactions. This study investigates their neuroendocrine influence on cerebral and retinal baseline vascular metrics across a healthy menstrual cycle. Twenty-six menstruating females completed imaging sessions and assessment of circulating hormone levels during their early follicular, late follicular and mid-luteal phase. Perfusion, arterial arrival time (AAT), global oxygen extraction fraction (OEF), cerebrovascular metabolic rate of oxygen (CMRO₂), carotid artery radius and carotid pulsatility index (PI) were measured using 3 T MRI. Retinal vessel density and blood flow resistance were assessed with optical coherence tomography angiography (OCT-A). Assessed with linear models, increased oestradiol was related to increased global perfusion (χ² (1) = 91.623; p = 1.049 × 10^-21) and decreased AAT (χ² (1) = 106.950; p = 4.575 × 10^-25). An independent progesterone increase was also associated with increased global perfusion (χ² (1) = 19.512; p = 9.998 × 10^-6) and decreased AAT (χ² (1) = 40.062; p = 2.46 × 10^-10). A relationship was also found between increased oestradiol and decreased retinal blood flow resistance (χ² (1) = 5.28; p = 0.0215), primarily driven by centrally localised vessels. This study finds that circulating oestrogen increases blood flow in the eye and brain, while progesterone is associated with brain perfusion increases alone. Both are associated with decreased cortical blood arrival speed. These effects suggest a potential pathway for neuroprotective mechanisms.