Enhanced Response to Oxytocin in Myometrium of Proven Breeder Compared to Virgin Rats Does Not Depend on Augmented Expression of Oxytocin Receptors

Objective Our overall hypothesis is that pregnancy’s mechanical and hormonal stimuli induce permanent changes in the properties of uterine tissue. We have shown previously that the response to oxytocin of the non-pregnant (NP) myometrium is more pronounced in proven breeder than in virgin animals. Our objective here was to investigate some of the possible mechanisms that could produce such difference: 1) Altered number of oxytocin receptors (OXTR); 2) Altered production of intracellular prostaglandins; 3) Altered availability of voltage gated calcium channels (VGCC). Method Virgin (V) and proven breeder (PB) NP female 18 week old rats were staged and euthanized at proestrus. One uterine horn was dissected in strips suspended in a tissue bath containing Krebs solution (in mM, NaCl 117, KCl 4.7, NaHCO3 25, MgCl2 1.2, KH2PO4 1.2, CaCl2 2.5, glucose 11, pH= 7.4) at 37°C and bubbled with 95% O2 and 5% CO2. Dose response curves to oxytocin (10E-10 to 10E-5 M) were recorded in the presence of indomethacin or aft...