Plasma kinetics of dihydroergotoxin in rat by using a radioreceptor assay

A radioreceptor assay (RRA) (with brain dopamine receptors) has been developed to determine the levels of dihydroergotoxin-equivalent (DHT-equivalent) material in rat plasma and its kinetics after oral and i.v. administration (5 mg/kg). After i.v. administration the plasma kinetics follows a two-exponential equation, with an apparent distribution volume of 7-9 1/kg and a long half-life (about 36 hours). The kinetics of DHT after oral administration shows two peaks; this could indicate a biliary recycling of the drug and/or of its metabolites. The low bioavailability (19%) and the biliary recycling of DHT-equivalent material suggest a first pass effect.