A new method for the investigation of endocrine-regulated autophagy and protein degradation in rat liver.

The effect of the antilipolytic agent 3,5-dimethylpyrazole (DMP) on liver autophagy and protein degradation was studied on male young adult rats (200 g body wt) of the Sprague-Dawley strain by electron microscopy and short-term single-pass liver perfusion and HPLC amino acid assay in the perfusate. Treatment with DMP (12 mg/kg body wt) enlarged the lysosomal-autophagic compartment in liver cells in 30 min and increased significantly the concentrations of valine and total amino acid in blood plasma (taken at sacrifice) and valine concentration in the liver perfusate in 60 min. These effects of DMP stimulating liver were secondary to the metabolic and endocrine effects of the drug (which caused a decrease in FFA, glucose, and insulin and an increase in glucagon and corticosterone plasma levels with a shorter latency, about 15 min). The effects of DMP were compared to those of other treatments inducing liver autophagy and protein degradation in vivo. Alterations after DMP or glucagon injections were similar, but they were larger and lasted for a longer time with DMP administration. Treatment with vinblastine or chloroquine enlarged the lysosomal-autophagic compartment without increasing protein breakdown.