Figure 3

Validation of the model for labor induction with oxytocin. (A) Visualization of uterine contraction. Upper panel: uterine myometrium harvested from pregnant E21 rats at least 8 h after either saline (control) or intravenous Oxt infusion and stained with hematoxylin. 20 × photomicrographs showing lack of clustering of uterine myocytes in saline-treated myometrium (left) compared to extensive clustering in the Oxt-exposed myometrium (right). Lower panel: 5-μm frozen sections from Oxt-exposed myometrium stained without (left) or with rabbit anti-mouse phosphomyosin light chain kinase showing prominent staining among clustered uterine myocytes revealed with anti-rabbit HRP conjugate (marked by arrows) (right). Nuclei counterstained with hematoxylin. Scale bar = 100 μM. (B) Labor induction with Oxt causes cyclical increases in intrauterine pressure. Labor was induced with Oxt at 48 h after pump implantation (around 12 noon, light cycle, E20) and intrauterine pressure changes were monitored with telemetry. Oxt initiation was associated with acute and cyclical increases in intrauterine pressure until birth (first pup delivered around 21:00 h, dark cycle, E20). Light and dark cycle from 07:00–19:00 and 19:00–07:00, respectively. (C) Labor induction with Oxt was associated with a significant increase in OxtR gene expression at 8–12 h. (D) Labor induction with Oxt decreases OxtR immunoreactivity in the rat uterus. Sample 20 × photomicrographs from 5-µm sections of the uterine myometrium stained with goat anti-rat OxtR antibody (1:100) and revealed with Alexa Fluor® 594 labeled rabbit anti-goat antibody (1:300). Note naïve uterine myometrium with bright staining for OxtR in the upper panel, in sharp contrast to Oxt-exposed myometrial tissue in the lower panel where staining was scant, suggesting downregulation of OxtR. Scale bar = 50 μM. (E) Representative cropped western blot images showing a decrease in membrane associated OxtR protein expression after labor induction with Oxt and quantified with densitometry. Full length blot is presented in Supplementary Figure S3. Please note that the Oxt and Con lanes have been cropped and reversed to present the data in a manner consistent with the rest of the manuscript (i.e., Con followed by Oxt data). Data analyzed with Welch’s t-test and presented as mean ± SEM; *p ≤ 0.05, **p ≤ 0.01.