Studies on the mechanism of bile salt-independent bile flow impairment in streptozotocin-induced hepatotoxicity.

The main factors involved in the impairment of formation of the bile salt-independent bile flow (BSIF) in streptozotocin (SZ)-treated rats were examined. Twenty-four hours after SZ injection (50 mg/kg body wt, i.v.) bile flow, bile salt output and biliary excretion of the major inorganic electrolytes (sodium, chloride and bicarbonate) were significantly diminished. The relationship between bile flow and bile salt output obtained during the administration of sodium taurocholate at stepwise-increasing rates indicated that bile salt-independent bile flow (y-intercept) was diminished by 37% in SZ-treated rats. The relationship between electrolyte output and bile salt output showed that the fractions of sodium, chloride and bicarbonate excreted independently of bile salt (y-intercept) decreased to 59%, 47% and 67% of the control values respectively, while the amount of electrolyte secreted per unit of bile salt secreted was unaffected in SZ-treated rats. The hepatic activity of Na+,K(+)-adenosine triphosphatase (Na+,K(+)-ATPase) was decreased by 59% (P less than 0.05) in SZ-treated rats. Nicotinamide administered prior to SZ prevented the hyperglycemia indicative of SZ-induced diabetes, but had no effect on the decrease in Na+,K(+)-ATPase activity caused by the drug. These results suggest that SZ itself, and not its diabetogenic effect, decreases the BSIF by a mechanism that involves impairment of the biliary electrolyte excretion, which could be the result of the inhibition of the hepatic Na+,K(+)-ATPase activity.