The pharmacokinetics and pharmacodynamics of bumetanide were investigated after intravenous (i.v.) administration, 10 mg kg-1, and oral administration, 20 mg kg-1, to spontaneously hypertensive rats (SHRs) and deoxycorticosterone acetate-salt induced hypertensive rats (DOCA-salt rats). After i.v. administration, the pharmacokinetic and pharmacodynamic parameters of bumetanide did not vary significantly between SHRs and the control Wistar rats. Similar results were also shown between DOCA-salt rats and the control Sprague-Dawley (SD) rats. After oral administration, the AUC0-12 h decreased significantly (186 versus 335 micrograms min ml-1) in SHRs and this resulted in decreased F(15.4 versus 23.6 and 2.78 versus 5.76% using two equations) in SHRs when compared with the control Wistar rats, although none of the other pharmacokinetic parameters varied significantly between SHRs and Wistar rats. This effect seemed to be due to the decreased enterohepatic recirculation of bumetanide in SHRs: the amounts of both bumetanide and its glucuronide product, which are capable of enterohepatic recirculation, excreted in 8 h bile juice decreased significantly in SHRs (11.3 versus 37.4 micrograms as expressed in terms of bumetanide) when compared with Wistar rats. The pharmacodynamic parameters did not vary significantly between SHRs and Wistar rats after oral administration of bumetanide. The pharmacokinetic and pharmacodynamic parameters of bumetanide did not vary significantly between DOCA-salt rats and SD rats after oral administration of the drug. The liver weights compared to body weight increased significantly in SHRs when compared with Wistar rats and the corresponding values for the kidney increased significantly in DOCA-salt rats when compared with SD rats.