Abstract
Treatment with the selective β3-adrenoceptor agonist BRL 37344 increased circulating levels of alanine transaminase (ALT) and aspartate transaminase (AST) in mice without causing hepatocellular injury. To clarify whether this was a β3-adrenoceptor-mediated effect, the inhibitory effect of the selective β3-adrenoceptor antagonist SR 59230A on the increase in circulating transaminase levels induced by BRL 37344 was examined. A single intraperitoneal dose of BRL 37344 alone initially increased insulin and non-esterified fatty acid (NEFA) dose-proportionally at 0.5 hr post-dose, findings considered attributable to β3-adrenoceptor-stimulating effects. Levels of the gluconeogenic precursors pyruvate (PA) and lactate (LA) were increased corresponding to the change in insulin. Thereafter, glucose (GLU) level was decreased at 4 and 8 hr post-dose, suggesting disruption of glucose homeostasis. In association with these changes in glucose metabolism, transaminase levels were increased maximally at 4 hr post-dose. The transaminase changes were not accompanied by increases in circulating levels of other hepatocellular enzymes, including guanine deaminase (GUA), glutamate dehydrogenase (GLDH), and lactate dehydrogenase (LDH), or any morphological hepatocellular injury. Intraperitoneal pre-treatment with SR 59230A partly inhibited the effects of BRL 37344 alone, indicating that the increase in levels of circulating ALT by BRL 37344 was attributable to a β3-adrenoceptor-stimulating effect. In conclusion, the β3-adrenoceptor agonist BRL 37344 was shown to increase circulating transaminase levels in mice accompanied with dynamic changes in glucose metabolism. These findings suggest the possibility that circulating transaminase levels are increased as pharmacological effects of drugs disrupting glucose metabolism, and that hepatotoxic markers should be selected considering these effects to distinguish between acceptable pharmacology and toxicity.
