Comparison of diestrus duration and temporal gene expression patterns in vaginal smear samples from pseudopregnant rats induced by sonic vibration or mating with vasectomized males

BACKGROUND: Induction of pseudopregnancy is a prerequisite for successful embryo transfer in rats. Conventionally, pseudopregnancy is induced by mating females with vasectomized males. Although effective, this method requires surgical preparation and maintenance of sterile males and may be affected by variability in mating performance. Artificial induction using sonic vibration has been proposed as a practical alternative; however, its comparability to the conventional method regarding the duration of the pseudopregnant state and temporal changes in the genes in the vaginal tissue has not been investigated. RESULTS: Pseudopregnancy was induced in Sprague-Dawley females either using sonic vibration or cohabitation with vasectomized males. The duration of pseudopregnancy was monitored via vaginal cytology. Vaginal smear-derived samples were collected during the first diestrus, middle diestrus, and the diestrus immediately before proestrus. Subsequently, the temporal expression of genes associated with estrus cycles (Filaggrin, Progesterone Receptor, Krt14, Il-1β, Zonula occludens-1, Occludin, Claudin1, Cdh1) was analyzed using quantitative real-time polymerase chain reaction. Generally, the duration of diestrus was longer when pseudopregnancy was induced by artificial stimulation (12-22 days) compared with that induced by a vasectomized male (10-12 days). Overall, the gene expression patterns in vaginal smear-derived samples were broadly similar between females subjected to sonic vibration and those mated with vasectomized males. CONCLUSIONS: Sonic vibration appeared to maintain a pseudopregnancy-like diestrus period for a longer duration than conventional mating-based methods. Changes in mRNA expression in the vaginal smear samples during the diestrus stage were similar between the two methods. Although further validation, including hormonal and uterine assessments, is needed, sonic vibration may represent a useful alternative method for reproductive engineering in rats by reducing the need for vasectomized males and simplifying colony management.