100 Estrous Cycle Ratio as a Reproductive Index in the Rats Copyright@ MJ Adeniyi --------------------------------------------------------------------------------------------------------------------------------- This work is licensed under Creative Commons Attribution 4.0 License AJBSR.MS.ID.000772 Review Article MJ Adeniyi 1 * and FO Agoreyo 2 1 Department of Physiology, Edo University Iyamho, Nigeria 2 Department of Physiology, University of Benin, Nigeria *Corresponding author: MJ Adeniyi, Department of Physiology, Edo University Iyamho, Edo state, Nigeria. To Cite This Article: MJ Adeniyi. Estrous Cycle Ratio as a Reproductive Index in the Rats. Am J Biomed Sci & Res. 2019 - 4(2). AJBSR.MS.ID.000772. DOI: 10.34297/AJBSR.2019.04.000772 Received: July 11, 2019 | Published: July 23, 2019 American Journal of Biomedical Science & Research ISSN: 2642-1747 www.biomedgrid.com Introduction Experimental rats are spontaneous ovulators with characteristic short reproductive cycle length lasting 4-5days [2]. Like the menstrual cycle, cyclic changes occur in murine reproductive structures, including the parenchyma of the ovaries-the primary reproductive organ. Examples of such changes are fluctuations in gonadotropin and gonadal hormones, changes in density of uterine glands and cervical mucus and perturbations in pH, sexual receptivity and body temperature [3]. Rats’ estrous is divided into four phases based on cell type and density. Proestrus is characterized by squamous epithelial cells. Estrus, metestrus and diestrus are identified and differentiated based on the presence and proportions of cornified cells, leucocytes and squamous epithelial cells. Like menstrual cycle, proestrus is related to pre-ovulatory phase. Metestrus and diestrus are related to post-ovulatory phase [2]. Several studies have evaluated estrous cycle using estrous cycle indices such as estrous cycle length, estrous frequency, estrous phase interval, estrous regularity and diestrus index [1]. The present study looked at the possibility and relevance of using estrous cycle ratio as a reproductive index in murine studies. Methodology Studies were retrieved through electronic databases of English language literature only. Search was achieved through the use of phrases and key words such as estrous cycle, estrous phases, estrus and estrous length. Murine studies published between 1999 and 2019 were selected. Only studies that displayed estrous phases in form of tables were used. Using these criteria, a total of 20 murine studies were selected. For each reviewed article, information was extracted on authorship and year of study. Only the placebo groups of these studies were analyzed. Calculation of estrous cycle ratio (ECR) was done using the method prescribed by [1]. ECR = (Proestrus+Estrus) / (Metestrus+Diestrus) Result See in the following (Table 1 & Table 2) Abstract Estrous cycle is an endogenous rhythm. Previously, studies have evaluated and analyzed the cycle based on its regularity and length and diestrus proportion. The aim of the review is to introduce estrous cycle ratio as a reproductive index and highlight its relevance. Twenty murine studies were retrieved from electronic databases published between 1999 and 2019. Estrous cycle ratio was calculated according to the method of [1]. The result shows that the average estrous cycle ratio is 0.81 with a nadir of 0.5 and a zenith of 1.5. Increase in estrous cycle ratio may signify prolongation of follicular phase length and delay in ovulation. Decrease in estrous cycle ratio may indicate delay in luteal regression with attendant delay in the initiation of new folliculogenesis. Therefore, estrous cycle ratio is an estrous cycle evaluation index. Keywords: Estrous Cycle Ratio; Follicular Phase; Folliculogenesis; Estrous Cycle; Ovulation Table 1: Estrous cycle phases. S/N Estrous Cycle Phases References Proestrus Estrus Metestrus Diestrus 1 25.0±0.3 17.0±1.8 29.0±0.3 29.0±0.3 Agoreyo & Adeniyi [1]