EFFECTS OF PHENOBARBITAL AND TAUROCHOLATE ON BILIARY EXCRETION OF IOPANOATE AND IOPHENOXATE IN THE RAT

¹ Department of Pharmacology and Toxicology and Department of Medicine, Dartmouth Medical School, Hanover, New Hampshire

Studies were performed on the effects of phenobarbital and taurocholate on the plasma decay and biliary excretion of iopanoate and ioplmenoxate in both male and female rats.Pretreatment of male rats with phenobarbital (40 mg/kg/day, three days) resulted in an increased plasma decay and biliary excretion after 5 and 50 mg/kg of iopanoate. This effect was associated with an increased liver content of labeled material at the end of the experiment (110 minutes). Similiar treatment of female rats also increased the plasma decay and biliary excretion of iopanoate, but only to that extent seen in control males. The constant infusion of taurocholate(1 µ/min) increased the biliary excretion of iopanoate during the early collection periods, but thereafter decreashed the excretion. This was not associated with a significant alteration in plasma decay or an overall increased biliary excretion. Neither phenobarbital pretreatment nor taurocholate infusion increased the biliary excretion of iophenoxate, although taurocholate caused a significant decrease in the plasma decay of iophimenoxate. These data suggest that the effects of phenobarbital and taurocholate on iopanoate and iophenoxatbe biliary excretion are not attributable to alterations in bile flow alone, Furthermore, these results suggest that taurocholate significantly alters the binding of iopanoate nsd iophenoxate to plasma and tissues.