Summary. An instrumental method/device for detecting of estrous stages in small rodents was tested in mice and rats. Cyclic changes in active resistance (RS) of the epithelial cell layer of vaginal mucosa were studied with a new mouse estrous detector device - MED-PRO 100 (Elmi Ltd., Latvia). The active resistance (AR) was measured at the frequency of 1 kHz by inserting the probe (l=14 mm, d=1.82 mm; measuring range – 0-50 kΩ) into the animal’s vagina for 1-2 sec. The use of small probe detector was compared to the classical vaginal smear collection procedure, using a lavage, and followed by cytological evaluation. The instrumental method was found to be similarly accurate, more expedient, less traumatic to an animal and less time consuming. The AR curves were quit similar during a few estrous cycles (especially in rats), and the AR changes corresponded to the cytological changes in vaginal smears. However, the maximum AR values corresponded to different stages of the cycle in mice and rats. In rats, the electrical AR was significantly higher at proestrus (over 5 kΩ), when compared to other stages of the estrous cycle, and statistically higher in metestrus, when compared to estrus and diestrus stages. In mice, the increase in AR occurred at the estrus stage. We conclude that the use of the MED-PRO 100 device provides an accurate approach to evaluate the estrous cycle in rats and mice. It can be used to determine an optimal time for animal mating, the use of hormonal superovulation or artificial reproduction technologies, as well as for optimization of behavioral, pharmacological and toxicological studies in female laboratory rodents.
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