Kidney Week

Abstract: FR-PO0983

Seasonal Changes in Osmosensitivity Among Postmenopausal Women in Tallahassee, Florida: A Pilot Study

Session Information

• Women's Health and Kidney Diseases
  October 23, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Women's Health and Kidney Diseases

• 2100 Women's Health and Kidney Diseases

Authors

• Domeier, Christin, Florida State University, Tallahassee, Florida, United States

Christin Domeier, MS, MSc

• Hoch, Jonathan, Florida State University, Tallahassee, Florida, United States

Jonathan Hoch

• Vondrasek, Joseph, Florida State University, Tallahassee, Florida, United States

Joseph Vondrasek, MS

• Bissen, Thomas G., Florida State University, Tallahassee, Florida, United States

Thomas G. Bissen, MSc

• Munoz, Colleen X., University of Hartford, West Hartford, Connecticut, United States

Colleen X. Munoz, MS, PhD

• Robinson, Austin, Indiana University, Bloomington, Indiana, United States

Austin Robinson, PhD

• Smith, Kyle, Florida State University, Tallahassee, Florida, United States

Kyle Smith, PhD, RD

• Watso, Joseph C., Florida State University, Tallahassee, Florida, United States

Joseph C. Watso, PhD

Background

Prior research indicated that arginine vasopressin (AVP) concentrations for a given blood osmolality (i.e., osmosensitivity) are suppressed in older compared to young males, and that this suppression is exacerbated during winter. However, it is unknown whether seasonal blunting persists in postmenopausal females in humid subtropical climates like Florida.

Methods

Thirteen healthy postmenopausal female participants (65 ± 5 years, body mass index: 23 ± 3 kg/m²) residing in Tallahassee, Florida, visited the laboratory in January (winter) and August (summer). Individuals with uncontrolled chronic conditions or those taking fluid-regulating medications (e.g., statins or diuretics) were excluded. Participants were instructed to wear an activity monitor (ActiGraph) and an individual-experienced temperature and humidity logger (Kestrel) for three full days before laboratory visits. We assessed plasma copeptin (a direct proxy for AVP; BRAHAMS Kryptor) and plasma osmolality (P_Osm) calculated from sodium (Na⁺), glucose, and blood urea nitrogen (BUN) concentrations in venous plasma samples (P_Osm = 2 x [Na⁺] + (Glucose / 18) + ([BUN] / 2.8)). We used linear mixed-effects models with copeptin as a dependent variable and P_Osm, ambient heat index, and physical activity as predictors.

Results

Ambient heat index significantly increased from winter to summer (winter: 70 ± 4 vs. 80 ± 4°F; p < 0.0001), but plasma copeptin (winter: 3.92 ± 1.80 vs. summer: 3.92 ± 1.97 pmol/L; p = 0.997) and P_Osm did not differ between seasons (winter: 287 ± 5 vs. summer: 285 ± 4 mOsm/kg; p = 0.161). Both P_Osm (β = 0.175; p = 0.032) and ambient heat index (β = 0.131; p = 0.038) were significant independent predictors of copeptin, whereas activity level was not (p = 0.946). Interestingly, osmosensitivity did not differ between seasons (p = 0.667).

Conclusion

These pilot data indicate that osmosensitivity is not altered between the winter and summer seasons in apparently healthy postmenopausal females living in Tallahassee, Florida, a humid subtropical environment. However, copeptin release may be sensitive to ambient heat exposure independent of osmotic stimulation or physical activity. This indicates that even in subtropical climates, seasonal shifts in ambient temperature may alter physiological demand, potentially affecting fluid balance during greater heat stress in postmenopausal females.

Acknowledgment

Funding: Florida State University Graduate School Legacy Fellowship (CD); K01HL160772 (JCW); Florida State University Institute for Successful Longevity (KAS & JCW)

Funding

• Private Foundation Support