Uterine expression of leptin, RhoA and Rho associated kinases in dogs with primary uterine inertia and with obstructive dystocia

Primary uterine inertia (PUI) is the most frequent dystocia in the bitch, but its etiology is still unclear. Knowledge about underlying functional and molecular changes in the uterus is very scarce. Obesity and high concentrations of leptin (major adipose derived hormone) are associated with complications of labor in women, and obese bitches are at increased risk of dystocia. In pregnant dogs, leptin is also produced by the uterus and placenta, so it may exert a negative paracrine/autocrine effect on uterine contractility during parturition. We hypothesized that high uterine leptin concentrations would adversely affect RhoA/Rho kinase pathway, which is involved in calcium sensitization, leading to decreased uterine contractions in dogs with PUI. Bitches presenting with dystocia (n = 18) were assigned to PUI (n = 11) or obstructive dystocia (OD) group (n = 7). Dogs in OD group were still showing strong contractions and were designated as controls. Dogs that received ecbolic or tocolytic medication were excluded. During cesarean section, a full thickness uterine biopsy was collected at an inter-placental site. Relative gene expression (RGE) of Lep, Lep receptor (LepR), RhoA and its effector kinases (ROCK1, ROCK2) was analyzed by real-time TaqMan qPCR. Immunohistochemistry or in situ hybridization was used for protein or mRNA localization, respectively. One-way ANOVA was used to compare uterine RGE between groups with body weight as covariate. Statistical significance was p < 0.05. Dogs were not obese (body condition score recorded for 14 dogs 3-6/9). Lep expression did not differ between groups. LepR mRNA levels were below detection limit in 5 PUI dogs and in all OD dogs. RhoA expression did not differ, but uterine ROCK1 and ROCK2 mRNA levels were higher in PUI dogs (p = 0.010 and p = 0.039, respectively). Lep, RhoA, ROCK1, ROCK2 protein, and LepR mRNA were all localized in myometrium, and staining intensity appeared similar between groups. Protein and mRNA signals were also present in endometrium and blood vessels. In conclusion, despite similar uterine leptin gene expression, undetectable LepR mRNA levels in OD dogs might indicate decreased responsiveness to potentially negative effects of leptin. However, ROCK1 and ROCK2 gene expression was lower in OD than in PUI dogs, which may be a physiological result of long-lasting, strong uterine contractions, and as such, could be an indication of abnormal progression of labor and insufficient uterine contractions in dogs with PUI.

Keywords: Uterine inertia, parturition, uterus, contractility, canine

Acknowledgement Financial support by Agria and SKK Research Foundation (no. N2014-0002)

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.