Tracer doses (1 μg.) of tritiated oestradiol-17β were administered to a healthy 36-year-old woman on the 19th day of a 29-day ovulatory cycle and the 6th day of the following cycle. Urine was collected for 5 days after each injection and was assayed for oestradiol, oestrone, oestriol and for radioactivity in these oestrogen fractions. The data were used to calculate the size of the oestradiol-plus-oestrone miscible body pool (approx. 227 μg. on day 19 and 61 μg. on day 6).
There was evidence that the label was mixed throughout most of the pool within a few hours of its injection.
The percentages of injected radioactivity excreted with the three oestrogens studied were similar for both studies. The oestriol recovery was greater than that reported by other investigators following injections of massive doses of oestradiol. The calculated endogenous production rate of oestradiol was approximately 165 μg./day on day 19 and 93 μg./day on day 6. The findings also indicated that oestrone and oestradiol were the source of essentially all endogenously produced oestriol.