Use of calibrated filter paper to evaluate vaginal moisture in mice

Abstract

The loss of ovarian estrogen production in postmenopausal women causes vaginal dryness and irritation. The contraceptive depot-medroxyprogesterone acetate (DMPA) likewise promotes vaginal dryness by suppressing ovulation and reducing estrogen production. Though vaginal dryness in women is typically identified by self-report, research with preclinical models will benefit from development of new methodology that objectively measures vaginal moisture. Strips of calibrated filter paper, similar to those used to quantify lachrymal secretions, were intravaginally placed in untreated ovary-intact mice, DMPA-treated ovary-intact mice, and ovariectomized (OVX) mice to measure vaginal fluid levels. As anticipated, levels of circulating estradiol were significantly lower in DMPA-treated and OVX mice vs. estrus-stage mice. Congruent with the loss of estrogen, median readings on calibrated filter paper strips collected from DMPA-treated (1 mm) and OVX mice (1 mm) were significantly lower than the median reading from estrus-stage mice (10 mm); (P < 0.0001 for both comparisons). Current findings indicate that calibrated filter paper provides objective measure of vaginal moisture in mice and suggest that the hypoestrogenemia produced in mice by DMPA injection or ovariectomization models the vaginal dryness detected in women with reduced levels of circulating estrogen.

Keywords: Calibrated filter paper strips; DMPA; Ovariectomized mice; Vaginal moisture.

Fig. 1

Quantifying vaginal moisture in mice. (a) Commercially available calibrated filter paper strips were trimmed for intravaginal insertion. (b) To ensure atraumatic insertion of these strips, 200 µL wide-bore pipette tips were shortened to 2.5 cm lengths and tip openings filed for smoothness. (c) Intravaginally inserted paper strips were retained for 5 min in sedated mice. (d) Representative results depict vaginal fluid levels as depicted by migration of the blue line on calibrated filter paper from its original position via capillary action.

Fig. 2

Vaginal fluid levels were significantly higher in estrus-stage mice vs. diestrus-stage, metestrus-stage, DMPA-treated, or OVX mice. (A) A median value of 10.0 mm (90% CI 7.5–15.0) was calculated from calibrated filter paper strips readings collected from estrus-stage mice (n = 15) while median readings of 1.0 mm (90% CI 0.1–1.0), 2.0 mm (90% CI 1.0–3.0), 1.0 mm (90% CI 0.1–1.5), and 1.0 mm (90% CI 0.5–1.0), respectively, were recorded from strips placed in metestrus-stage (n = 15), diestrus-stage (n = 15), DMPA-treated (n = 20) and OVX mice (n = 15). Data shown are pooled from two independent experiments. (B) Serum estradiol levels were comparable between DMPA-treated (n = 15) and OVX mice (n = 15) and significantly lower than values measured in untreated mice in the estrus stage of the estrous cycle (n = 15). Serum samples measuring estradiol were performed in triplicate. DMPA, depot-medroxyprogesterone acetate; OVX, ovariectomized.