Preferential transfer of endogenous ovarian steroid hormones to the uterus during both the follicular and luteal phases

BACKGROUND: Ovarian steroids are thought to be released into the systemic circulation and reach the uterus via the uterine arteries. However, results of experimental and clinical studies suggest the existence of local transfer of steroids from the ovary to the uterus. This study aimed to verify the existence of preferential distribution of ovarian steroids to the uterus in the two phases of the menstrual cycle. METHODS: We performed parallel measurements of serum levels of estradiol and progesterone in the systemic circulation (arterial and venous) and in the uterine vessels in two groups of cycling women; one group were in the follicular phase (six women) and the other group were in the luteal phase (10 women) of the menstrual cycle. RESULTS: Both in the follicular phase and in the luteal phase groups, mean estradiol levels in the uterine blood were significantly higher than in both sides of the systemic circulation (F=7.30, df =15, P<0.006; and F=4.70, df =27, P<0.02). Similar results were obtained in the luteal phase group for progesterone (F=9.38, df =27, P<0.0001). Both estradiol and progesterone levels in arterial and venous systemic blood were similar. CONCLUSIONS: The results of this study demonstrate that ovarian steroid levels are significantly higher in the uterine vessels than in both sides of the systemic blood circulation, and strongly suggest the existence in the female pelvis of mechanisms of local distribution of ovarian hormones.