Studies on the Metabolic Fate of a New Thromboxane A2 Receptor Antagonist, S-1452 (III) : Transfer into the Fetus and Milk in Rats

Transfer of radioactivity into the fetus and milk were studied after a single oral administration of 14C-S-1452 at a dose of 5mg/kg in pregnant rats on 19 days of gestation and in lactating rats. 1. In whole body autoradiography, distribution patterns of radioactivity in maternal tissues were similar to those found in male rats. 2. The distribution of radioactivity in a fetus at 1 hr after administration was estimated to be 0.04% of the administered dose. This result suggests that fetal transport of S-1452 is relatively low in rats. 3. At 24hr after administration, the radioactivity in maternal tissues and in the fetus had been almost completely eliminated. 4. The level of radioactivity in the milk was one-third of that in the plasma at 30 min after administration. From 2 to 6hr after administration, higher levels were found in the milk. However, at 24hr after administration, the level was similar to that in the plasma.