(36) Hormone Variability, Lean Soft Tissue, and Muscle Quality Predict Variability in Adipose Tissue Blood Flow in Perimenopausal Females.

Purpose: Perimenopause is marked by fluctuations in estrogen (E2) and progesterone (P4), which contribute to alterations in body fat percentage (BF%), lean soft tissue (LST) and muscle quality. Adipose tissue (AT) blood flow is a key determinant in regulating fat metabolism, influencing the balance between lipid mobilization (lipolysis) and deposition. Hormonal and body composition changes during perimenopause may impair AT blood flow and favor fat storage leading to reduced lipolysis and systemic fat oxidation, as indicated by lower glycerol and an elevated respiratory quotient (RQ), respectively. To examine the impact of E2/P4 ratio, BF%, LST, RQ, and muscle quality on AT blood flow and glycerol concentrations in perimenopausal females. Methods: Nine perimenopausal females (age: 49±5 years; BMI: 31.6±3.31 kg/m²) completed a whole-body dual-energy X-ray absorptiometry to measure BF% and LST (kg). Indirect calorimetry was conducted over a 25-minute period to assess respiratory quotient (RQ). Muscle quality was evaluated by echo intensity (EI; a.u.) in the vastus lateralis with ultrasound. At two separate visits (+ >7 days), microdialysis probes were inserted into the abdominal subcutaneous AT to measure resting AT blood flow and glycerol concentrations. Urinary hormone concentrations (E2, P4) were measured using a smartphone diagnostic device. Variability was calculated as the difference between visits. Pearson correlations examined associations between body composition (BF%, LST, EI), RQ, E2/P4 ratio, and in vivo AT blood flow and glycerol concentrations, with age as a covariate. Multiple linear regression models were used to understand the contribution of LST, EI, RQ, BF%, Age, and E2/P4 ratio on AT blood flow and glycerol variability. Results: AT blood flow was negatively associated with E2/P4 ratio (r=-0.76, p=0.01), but not BF% (r=0.61, p=0.08), LST (r=0.59, p=0.09), or EI (r=0.19, p=0.63). AT glycerol concentrations were not significantly associated with E2/P4 ratio, BF%, LST, or EI (p >0.05). LST, EI, and E2/P4 variability were significant predictors of AT blood flow variability between visits (r2=0.92, p=0.04). LST, EI, BF, RQ, and E2/P4 ratio variability were not significant predictors of AT glycerol variability between visits (p >0.05). Conclusions: These data suggest that greater AT blood flow was associated with a lower E2/P4 ratio. AT blood flow was predicted by LST, EI, and E2/P4 ratio variability. However, AT glycerol concentrations were not significantly predicted by any of the examined variables. Practical Applications: While hormonal fluctuations are inherent to perimenopause, this study suggests that variations in LST, EI, E2/E4 ratio significantly influence AT blood flow, a key determinant of fat metabolism and storage. These findings highlight the potential for targeted exercise and nutritional interventions aimed at enhancing LST and muscle quality to reduce variability in AT blood flow and potentially mitigate excess adipose accumulation in perimenopausal women. However, LST, EI, RQ, BF%, and the E₂/P₄ ratio did not significantly account for the variability in AT glycerol concentrations, suggesting that additional regulatory factors influence lipolysis during perimenopause. Acknowledgements: This study was supported by a grant from the American Diabetes Association.