PHYSIOLOGICAL DISPOSITION OF ³H-QUINESTROL

The absorption, distribution and excretion of ³H-quinestrol (³H-EECPE), labelled at C-9 and C-11, were studied in female rats and two rhesus monkeys. The absorption of ³H-EECPE from the gastrointestinal tract was a relatively slow process, as evidenced by the finding that the biological half life of ³H-EECPE in the gastrointestinal tract was 13 hours. Radioactivity was detectable in the blood of rats 30 minutes after oral administration, However, the radioactivity did not rise to its peak level until 10 hours after administration. In one monkey radioactivity was detected one hour after oral administration of ³H-EECPE and rose to its peak level in 4 hours. After absorption of ³H-EECPE, radioactivity was found to be highest in the fat tissues and fairly high in the brain, while in the target organs (uterus, oviduct and breast)radioactivity was rather low ³E-EECPE seemed to be stored for long periods of time in various tissues after absorption as shown by the sustained radioactivity in these tissues. This was especially so with the fat tissue as could be exemplified by the detection of fairly high radioactivity in the fat tissue of a monkey 21 days after administration of ³H-EECPE. ³H-EECPE was excreted mainly by the fecal route, while the renal route of excretion was of less importance. AS a consequence of prolonged storage in the body tissues, clearance of ³H-EECPE from the body was relatively slow. The amount of radioactive material excreted in the feces and urine 15 days after oral adminidtration of ³H-EECPE to rats was 34.1% of the amount ingested and that excreted by a monkey three weeks after administration was 53.8% of the dose.