Utero-ovarian interactions during early pregnancy: role of conceptus-induced vasodilation.

Recent studies of utero-ovarian blood flow have indicated an interaction between the gravid uterus and the ovary in maintaining luteal function during early pregnancy. On days critical for the continuation of pregnancy, blood flow to the corpus luteum (CL) increases several-fold, coincident with an increase in concentrations of progesterone (P4) in systemic blood. Enhanced ovarian secretion of P4 may amplify the vasodilatory "signal" of the conceptus and thus ensure an adequate uterine blood supply to support early fetal growth. Utero-ovarian vasodilation during early pregnancy may not only stimulate luteal function directly but also enhance transport of luteotropic substances to the ovary. Possible candidates for the vasodilatory factor(s) secreted from the early gravid uterus include estrogens and prostaglandins (PG) E. In addition, conversion of estrogens to their catechol forms, which have both vasodilatory and luteotropic activities, may be important for the successful establishment of pregnancy.