Decidual Tissue Growth and Regression in the Guinea Pig: Regulation by Uterine Blood Flow and Relation to Circulating Progesterone Concentrations*

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Abstract
The role of uterine blood flow (UBF) in the modulation of experimentally-induced decidua formation was assessed in mature guinea pigs. The response to endometrial trauma, as indexed by uterine weight changes, was dependent upon the type of stimulus used with deciduogenic effectiveness as follows: saline = oil = knife scratch < scissor cut. Both the knife scratch and scissor cut techniques induced elevations in UBF compared with control values. Neither uterine weight nor UBF increased when trauma was applied to unresponsive uteri, indicating that inflammation was not the cause of uterine hyperemia. Uterine weight increased from basal levels on the day of trauma (i.e., day 5 of the estrous cycle) to a maximal weight between days 10 and 12 posttrauma. Maximal growth of the induced decidua occurred under conditions of elevated UBF. Subsequently, UBF declined between days 10 and 15 posttrauma, preceding the associate resorption of the induced decidua. During the period of decidua growth, serum progesterone levels were elevated compared with those in control animals. Experimentally-induced decidua formation in the guinea pig is associated with uterine hyperemia and increased corpus luteum activity, both of which are necessary for proper endometrial differentiation. Apparently these events mimic the uterine hyperemia associated with blastocyst implantation and early placentation in this species.