The non-pregnant uterus shows different patterns of contractility during the menstrual cycle. A renewed interest in uterine contractility has resulted from reports of non-invasive ultrasound (US) based studies. To clarify the changes in uterine contractility occurring throughout the menstrual cycle, we prospectively studied uterine contractions (UC) at six representative stages with US and intrauterine pressure (IUP) based approaches in 30 cycling volunteers. Results showed UC frequency could be measured by either US or IUP. UC amplitude and resting pressure tone could only be assessed by IUP. Conversely, direction of UC displacement could only be assessed by US. UC frequency increased at mid-cycle and decreased throughout the luteal phase suggesting oestradiol and progesterone exert positive and negative actions on uterine contractility, respectively. UC amplitude increased throughout the menstrual cycle to maximum values in the late luteal phase. Retrograde UC were most frequent at mid-cycle and convergent ('opposing') UC predominated during the luteal phase. While the former pattern ensures sperm transport, the latter may facilitate embryo implantation. In conclusion, UC changes throughout the menstrual cycle assessed by US and IUP emphasize the hormonal dependence of uterine contractility. Although UC patterns favouring sperm transport appear regulated by oestradiol, uterine quiescence and the dominance of convergent UC prevailing at the time of implantation are linked to progesterone. These data will serve to identify and treat possible dyskinetic changes in uterine contractility, particularly in women suffering from infertility, endometriosis, and dysmenorrhea.

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The objective was to verify the hypothesis of a 'first uterine pass effect' or direct preferential vagina-to-uterus transport, suggested by the evidence of higher than expected uterine tissue concentrations after vaginal administration of progesterone; we used a human ex-vivo uterine perfusion model. A mixture of tritiated (3H) and unlabelled progesterone was applied to the cuff of vaginal tissue remaining attached to the cervix after hysterectomy. At the end of the perfusion period (up to 12 h), 3H and 14C radioactivity was measured in samples of uterine tissue. Tritiated water and [14C]dextran were tested to determine the extent of non-specific vagina-to-uterus transport (leaks). Finally, sections of uterine tissue exposed only to [3H]progesterone were prepared for autoradiography. By 4-5 h after application progesterone had diffused to the entire uterus and had reached a steady state; 4 h after application, progesterone concentrations reached 185 +/- 155 and 254 +/- 305 ng/100 mg of endometrial and myometrial tissue respectively. Endometrial extraction of progesterone was higher when the experiment was performed on uteri obtained during the luteal phase (280 +/- 156 ng/100 mg of endometrial tissue) than those removed during the proliferative phase of the menstrual cycle (74 +/- 28 ng/100 mg of endometrial tissue). These data demonstrate that a 'first uterine pass effect' occurs when drugs are delivered vaginally, thereby providing an explanation for the unexpectedly high uterine concentrations relative to the low serum concentration observed after vaginal administration. Hence, the vaginal route permits targeted drug delivery to the uterus, thereby maximizing the desired effects while minimizing the potential for adverse systemic effects.

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