Fate of peritoneal progesterone in the rabbit.

The efficiency of peritoneal absorption of progesterone was investigated by following the appearance of 3H-progesterone and its metabolites in the circulation after intravenous or intraperitoneal administration. Tritium rapidly entered the peripheral circulation when given by either route. The percentage of tritium appearing as modified progesterone was substantially lower following intraperitoneal administration. This difference can be largely attributed to splanchnic absorption and hepatic metabolism of intraperitoneal steroids. The potentially large amount of progesterone secreted into the peritoneal compartment may not contribute significantly to the peripheral circulating pool of progesterone.