Does Menstrual Cycle Phase Impact the Brachial Artery Flow Mediated Dilation Response to Acute Hyperglycemia?
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Acute hyperglycemia transiently impairs endothelial function in healthy males when assessed via flow-mediated dilation (FMD). However, research in female participants is lacking and the impact of menstrual phase (early follicular (EF) and late follicular (LF)) on vulnerability to acute hyperglycemia-induced endothelial dysfunction is unknown. It is hypothesized that hyperglycemia-induced endothelial dysfunction will be attenuated in the LF phase. Seventeen healthy, naturally menstruating women (21 ± 1 years [mean ± SD]) participated in three experimental visits. During two visits (one EF phase, one LF phase), endothelial function was assessed via brachial artery FMD before and 60-, 90-, and 120-min after an oral glucose challenge (75g glucose/300mL solution). Blood samples were taken to assess blood glucose, insulin, estradiol, progesterone and viscosity. During a third visit in the EF phase, participants ingested 300mL of water as a time-control for FMD. Blood samples were only taken for blood glucose and viscosity during this visit. Additionally, ovulation testing was used to confirm the LF phase. Data are [mean ± SD]. Glucose and insulin levels increased 30min post-glucose ingestion, with no difference between visits (p < 0.001). FMD was reduced 90min post-glucose ingestion (Post90) during the EF glucose visit (Pre: 8.7 ± 2.9%, Post90: 6.2 ± 2.8%, p = 0.001; Cohen’s d = 0.864). FMD-impairment during LFGlucose was not significant (Pre: 8.4 ± 2.4%, Post120: 6.8 ± 2.7, p = 0.089; d = 0.649). A direct comparison of EF and LFGlucose delta-FMD did not reach significance (p=0.117) revealing a small effect of phase (d = 0.431) on vulnerability to hyperglycemia-induced FMD impairment. These results suggest that the cyclic elevation in estrogen that occurs during the menstrual cycle confers a small degree of protection from acute hyperglycemia-induced impairment in endothelial function. In order to fully characterize the impact of acute stimuli on vascular function in premenopausal women, it is essential to examine responses across multiple phases of the menstrual cycle.