Involvement of Oxytocin and Progesterone Receptor Expression in the Etiology of Canine Uterine Inertia.

An altered oxytocin and progesterone receptor ( and , respectively) expression was postulated in canine uterine inertia (UI), which is the lack of functional myometrial contractions. and expressions were compared in uterine tissue obtained during C-section due to primary UI (PUI; = 12) and obstructive dystocia (OD, = 8). In PUI, the influence of litter size was studied (small/normal/large litter: PUI-S/N/L: = 5/4/3). Staining intensity in immunohistochemistry was scored for the longitudinal and circular myometrial layer and summarized per dog (IP-Myoscore). Mean P4 did not differ significantly between PUI ( = 9) and OD ( = 7). and expressions (ratios) were significantly higher in PUI (: = 0.0019; : = 0.0339), also for in PUI-N versus OD ( = 0.0034). A trend for a higher IP-Myoscore was identified (PUI-N vs. OD, = 0.0626) as well as an influence of litter size (lowest -Myoscore in PUI-L, = 0.0391). In conclusion, PUI was not related to higher P4, but potentially increased availability compared to OD. It remains to be clarified whether is upregulated in PUI due to a counterregulatory mechanism to overcome myometrial quiescence or downregulated in OD due to physiological slow desensitization associated with an advanced duration of labor. Identified differences between myometrial layers indicate the need for further research.