Deciduoma Growth in the Ovariectomized Guinea Pig: Steroid Hormone-mediated Vascular Support of Endometrial Differentiation

The ability of ovarian steroid hormones to modulate experimentally induced decidual tissue (DT) growth and the associated changes in uterine blood flow rates (UBF) was examined in ovariectomized guinea pigs after uterine trauma (designated day 0 of the studies). Uteri that were exposed, but not manipulated, served as controls. Uterine and DT weights as well as UBF, rates, were subsequently recorded on either day 5 or 10 posttrauma. Oil treatment failed to induce an increase in either control or traumatized uterine weights between days 5 and 10, and trauma had no effect on UBF rates in either group. Daily progesterone (P; 2 mg) treatment induced a significant elevation in DT weight by day 10 and elevated UBF rates between days 5 and 10 relative to control values. Daily P treatment augmented by estradiol (E2; 1 microgram) therapy on days 0 and 1 induced a significant increase in DT weights and UBF rates between days 5 and 10 in both control and DT groups relative to those in oil-treated animals. Combined P and E2 (P/E2) treatment induced a moderate increase in DT weight by day 10 posttrauma and elevated UBF rates in both control and DT groups. Acute treatment (i.e. days -3 to 0) with these steroid regimens indicated that neither P nor P/E2 treatment maintained DT growth. However, day -3 to 0 treatment with P in combination with a single day 0 injection of E2 allowed for maximal DT growth by day 10 and maintained elevated UBF rates relative to control values. P/E2 treatment between days -3 and 0 also induced an increase in UBF rates in both control and DT uteri relative to those in oil-treated animals. These results indicate that E2 is essential for supporting the P-directed differentiation and proliferation of stimulated guinea pig endometrium into DT. The ability of decidualization to occur in the absence of chronic steroid support indicates that uterine sensitization for cellular differentiation in this species only requires that the endometrium be initially primed by ovarian steroid hormones, but that subsequent growth is autonomous.