EFFECTS OF CLONIDINE AND IBMX ON SULFOBROMOPHTHALEIN DISPOSITION IN RATS

Clonidine, an alpha(2)-adrenoceptor agonist, inhibited the biliary exc retion, reduced the plasma clearance and increased the hepatic retenti on of sulfobromophthalein (BSP) in a dose related fashion in rats. The maximal effects of clonidine on BSP disposition occurred about 4 h af ter pretreatment. The effects of clonidine on biliary excretion and he patic retention of BSP were retained following laparotomy (with or wit hout bile duct cannulation); however, the effect of clonidine on plasm a disappearance profile was not retained following abdominal surgery. Isobutylmethylxanthine (IBMX) affected BSP disposition in a similar fa shion as clonidine, in rats without bile duct cannulation only; no eff ect of IBMX could be observed in bile duct cannulation rats. Yohimbine , an alpha(2)-adrenoceptor antagonist, reversed the effects of clonidi ne, but not of IBMX on BSP disposition. It thus seems that clonidine a nd IBMX exert their effects on BSP disposition by different mechanisms and probably at different sites.