Clearance of a tritium-labeled progestin in the ewe.

Abstract

Pessaries impregnated with 9a-fluoro-γ-11β-hydroxy-17 a-acetoxy progesterone-1, 2-3H were inserted intravaginally in three open, anestrus ewes, one open, lactating ewe and one pregnant ewe. An open, anestrus ewe received an untreated pessary and served as a control. Radioactivity in blood, milk, feces and urine was measured daily while the pessaries were in place (20 days) and for as long as 20 days after their removal. Liver, fat and muscle biopsies were taken periodically throughout the trial. At autopsy tissues were collected to determine residual radioactivity. Between 12 and 24% of the dose was absorbed from the pessary. Of the absorbed dose 84 to 100% was recovered in feces and urine. Excretion was almost equally partitioned between feces and urine, and milk was not a significant excretory route. The half life of the dose remaining after pessary removal was 1.2 days. Tissue levels of radioactivity remained low throughout the trial. The pregnant ewe had the highest levels of radioactivity in blood, milk and excreta and cleared radioactivity at a high rate. The chorio-allantois and fetal heart were high in radioactivity, although the counts in fetal liver did not exceed those of the dam. Three of the open ewes were free of counts in blood, feces and urine within 4 days after withdrawal, but one ewe continued to excrete radioactivity for 17 days.