Selective autophagy of clofibrate-induced rat liver peroxisomes. Cytochemistry and immunocytochemistry on tissue specimens and on fractions obtained by Nycodenz density gradient centrifugation

Following short treatments with peroxisomal proliferators rodent liver unde rgoes a significant increase in the peroxisomal population, accompanied by specific induction of some peroxisomal enzymes; both phenomena are reversib le and in a few days after drug withdrawal the control parameters are recov ered. The involvement of lysosomal system in removal of proliferated peroxi somes has been widely suggested, and the autophagic phenomenon was mainly i nvestigated in experimental conditions in which the administration of lysos omotropic drugs or, more generally, of digestive process inhibitors caused an accumulation of autophagic vacuoles. In the present research the removal of clofibrate-induced rat liver peroxisomes was investigated under physiol ogical conditions, i.e. in the absence of drugs interfering with the autoph agic process. In a previous paper the lysosomal Involvement in peroxisomal removal was suggested on the basis both of biochemical and cytochemical-imm unocytochemical data In the present paper the autophagic vacuoles and autol ysosomes involved in the digestion of excess peroxisomes are more extensive ly described, mainly by means of colloidal gold immunocytochemistry, carrie d out also on density gradient subfractions.