LIVER PEROXISOMES IN NEWBORNS FROM CLOFIBRATE-TREATED RATS .1. A MORPHOMETRIC STUDY OF THE RECOVERY PERIOD

Morphological and morphometric parameters (volume density (V(v)), numerical density (N(A)) and mean diameter (DBAR)) of newborn liver peroxisomes were measured throughout the first week of life in rats born to mothers treated with clofibrate (ethyl 2 p-clorophenoxy isobutyrate) during the last five days of pregnancy. In control studies the same analyses were carried out in newborns from untreated rats. At birth (day 0), treated animals exhibited a proliferated, pleiomorphic peroxisomal population (higher V(v), N(A) and DBAR, and a spread distribution of profile diameter with respect to the controls). In the subsequent two days, many peroxisomes disappeared (decrease of V(v) and N(A) to values even lower than controls), with a persisting high pleiomorphism (no change of DBAR and diameter distribution) in residual ones. Starting from day 3, and up to day 6, larger peroxisomes were no longer detectable in test animals, and a significant, not pleiomorphic proliferation took place (DBAR and diameter distributions strictly comparable to the controls and progressively increasing, V(v) and N(A)). The correlation analysis validated these morphological results, from which it can be surmised that the postnatal peroxisome recovery period consists of a destructive phase followed by a proliferative one. The possible mechanism(s) of disposal of the excess of drug-induced peroxisomes are discussed.