Stimulation of uterine RNA synthesis in mice by the post-coital antifertility agent, ORF 3858.

Abstract

Stimulation of uterine ribonucleic acid (RNA) synthesis in mice by t he postcoital antifertility agent ORF 3858 was investigated. .1 mcg of ORF 3858 or its parahydroxylated congener ORF 5531 was injected sc into female mice which weighed 25-30 gm and had been ovariectomized 14-18 days previously. The mice received 6 mcCi tritiated uridine via the lateral tail vein at various times after the antifertility agent. At autopsy the uteri were removed. RNA synthesis was measured by a modified method of Miller and Emmens. The baseline rate of tritiated uridine incorporation in uterine RNA was 40 dpm/mg wet weight/hour. ORF 5531 caused an immediate decrease in the rate of RNA synthesis to a 4.7-fold peak within 8 hours. ORF 3858 remained without change at background levels for several hours before it increased to a maximum rate 2.5 times the background rate after 16 hours. 32 hours postinjection the rate induced by both returned to levels slightly below the baseline rates. It is concluded that the postcoital antifertility action fo ORF 3858 lies in its activity as a proestrogen.