Using Vaginal Impedance Measurement to Identify Proestrus in Rats Given Luteinizing Hormone Releasing Hormone (LHRH) Agonist

Abstract

Vaginal cytology is the most common method of monitoring the estrous cycle in rats; however, this test requires specific technical training and can be subject to interpretation. Vaginal impedance offers a quicker and less technically challenging alternative and has been used successfully to identify estrus in normally cycling breeder rats. We hypothesize that vaginal impedance can also be used to stage the estrous cycle in rats that have been given luteinizing hormone releasing hormone (LHRH) for timed mating. Vaginal impedance measurements and vaginal cytology were performed in LHRH-primed female rats (n = 36) at the expected peak of proestrus and paired with proven stud males. Breeding success was determined by gross necropsy to detect embryo implantation sites in the female rats. We found that the predictive rates of vaginal cytology and impedance measurement for proestrus were similar; however, both methods resulted in high proportions of false positive and false negative determinations (28% and 31%, respectively). We further hypothesized that females respond to LHRH at variable rates, resulting in variable times of peak proestrus. To test this, vaginal impedance measurements were performed multiple times throughout the expected day of proestrus in LHRH-primed female rats (n = 36). Females were either paired with a male 24 h after reaching the proestrus threshold (n = 18) or paired according to our standard protocol at 1300 h on the day after the expected proestrus (n = 18). Sequential measurements reduced false positive and negative rates (14% and 8%, respectively). Pregnancy rates did not differ based on the time of pairing during expected estrus. Overall, we determined vaginal impedance can be more successful than vaginal cytology at identifying proestrus in the rat, but only if multiple measurements are taken.

Inhibition of the Sodium–Calcium Exchanger Reverse Mode Activity Reduces Alcohol Consumption in Rats

“…A plastic probe (4.5 mm in diameter) containing two silver ring electrodes was inserted into the vagina and held stable to ensure complete contact with the metal electrodes. A threshold ≥3.0 kΩ was used to confirm the proestrus phase, while the estrus phase was characterized by a <3.0 kΩ [60]. The vaginal impedance readings provide a more accurate method of determining phases of the estrous cycle than vaginal smear cytology [60,61].…”

“…A threshold ≥3.0 kΩ was used to confirm the proestrus phase, while the estrus phase was characterized by a <3.0 kΩ [60]. The vaginal impedance readings provide a more accurate method of determining phases of the estrous cycle than vaginal smear cytology [60,61].…”

Track-by-Day: A standardized approach to estrous cycle monitoring in biobehavioral research

“…Some cycles did have a surge in leukocytes on Day 2 (Figure 3j), consistent with the definition of metestrus, but this did not occur in all rats (Figure 3k) and was not consistent within rats across the two cycles (Figure 3l). Vaginal impedance has been reported to change over the estrous cycle and has been advocated as an easy alternative to cytology for cycle tracking [41][42][43][44] , although one study found no correlation between impedance and serum hormone levels 45 . We measured impedance at the time of most swab collections and found that it varied over the cycle in all animals (Figure 3m).…”

A study on the correlation between vaginal conductivity and estrus in Hanwoo (Bos taurus coreanae) cows

“…During the estrus, cows demonstrate characteristics such as mounting, increased body temperature and activity, and copious vaginal mucus discharge which is commonly observed around the vulva and in the tail (Talukder et al, 2018, Higaki et al, 2019. Recent studies measuring vaginal electrical resistance values in ewes, sows, female dogs, red foxes, and rats, and analyzed its correlation with estrus in Japanese Black heifers and cows have been reported (Talukder et al, 2018, Yatu et al, 2018, Higaki et al, 2019, Chesney et al, 2020, Lindh et al, 2020, Glencorse et al, 2023. However, there are no studies measuring vaginal electrical resistance in Hanwoo cows.…”