A technique was developed to measure water exchange in the endometrical canal (uterine cavity). This type of determination should provide information necessary to understanding intrauterine pharmacokinetics. In the study described, measurements were performed on one cynomologus and four rhesus monkeys. Endometrial fluid in the uterine cavity was replaced with a 3H2O solution of known specific radioactivity (dpm/ml). Radioactivity remaining in the cavity at measured intervals of approximately 0.5, 1, 2, and 3 min following replacement was determined by flushing out the cavity. By extrapolating the 3H2O disappearance curve versus time to t = 0 (zero time), the apparent cavity volume (aVc) was derived. Values for aVc and t 1/2 3H2O were used to calculate endometrial fluid-water turnover rate. Mean values determined in four rhesus monkeys were as follows: aVc, 0.032 ml; t 1/2 H2O, 1.17 min; 24-h H2O turnover, 19.5 ml. In general, this value for H2O turnover was considerably higher than values of endometrial fluid production quantitated by other techniques. Water measurements in human uteri similar to those reported here appear feasible and are anticipated in future work.

An improved method of measuring menstrual blood loss (MBL) in rhesus monkeys is developed and appears to be accurate within ± 10% of actual loss. MBL and intraindividual variations of MBL are measured in three groups of captive rhesus monkeys: intact, with surgical uterocutaneous fistulas, and ovariectomized with fistulas. On a volume per body weight basis, MBL of healthy, non-anemic women compares favorably to that of healthy female rhesus monkeys. Using duration of menses as an index of MBL is found to be of little value in practical applications.

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