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EFFECTS OF A WATER BOLUS IN ORAL CONTRACEPTIVE USERS

Abstract

Whitley C. Atkins1, Brendon P. McDermott, FACSM1, Abigail T. Colburn2, Stavros A. Kavouras, FACSM2

1University of Arkansas, Fayetteville AR; 2Arizona State University, Phoenix, AZ

Complicating the understanding of fluid balance in females, oral contraceptive (OC) use has increased in recent decades. Changes in exogenous hormone concentrations may alter body fluid balance. PURPOSE: Determine the fluid balance response to a water bolus given during active pill (high hormone, HH) versus sham pill dosing (low hormone, LH) of combined estrogen and progesterone, monophasic OCs. METHODS: 15 women (25± 5 y, 60.2±7 kg, 38.7±3.2 kg/LBM) completed two randomized trials. Participants were long-term OC users (≥ 6 months). Experimental trials were scheduled so that participants were on the active pill dose of prescribed OCs for one trial and the placebo or sham dose for the other. Participants arrived at the research center at 7 AM euhydrated (urine specific gravity, USG ≤ 1.020) and were fed a standard breakfast. Participants remained seated for 60 min and a blood sample was collected. Participants voided their bladder, and a nude body mass (NBM) was recorded. Room-temperature water was provided over 20 min in four equal boluses (3 mL/kg/LBM). Urine voids were collected. After 180 min, NBM was measured and a blood sample was collected. USG was analyzed via refractometry and urine osmolality was analyzed via freezing point depression. Serum copeptin concentration was analyzed from single samples using immunofluorescent Copeptin proAVP KRYPTOR assay via the KRYPTOR Compact PLUS analyzer. Copeptin concentration comparisons were made using a two-way ANOVA with repeated measures. Dependent t-tests were used to assess mean differences in urinalysis. RESULTS: Copeptin concentration did not differ between phases of OC use (p=0.645) nor from pre- to post-trial (p=0.787) (HH pre: 3.102±1.721, HH post: 2.953±1.249, LH pre: 3.171±1.950, LH post: 3.314±1.354 pmol/L). 3-hr urine volume was not different between HH (767±201 mL) or LH (748±202 mL; p=0.780). There were no differences between 3-hr USG (HH: 1.005±0.001, LH: 1.005±0.001; p=0.656) or 3-hr osmolality (HH: 193±40, LH: 203±60 mOsm/kg; p=0.485). NBM change did not differ between trials (HH: 0.29±0.36, LH: 0.44±0.29 kg, p=0.151). CONCLUSION: In euhydrated, resting conditions, fluid balance was unaffected by hormone phase of OC after consumption of a water bolus. Further research is needed to extend findings to varying exercise modalities and environments.

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