Nucleic acid synthesis in proliferating peroxisomes of rat liver as revealed by electron microscopical radioautography.

Thirty albino rats were fed with a diet containing 1, 2 or 4% di-(2-ethylhexyl)-phthalate (DEHP), a peroxisome-proliferating agent. Others were fed with normal diet as controls. Both groups were sacrificed at varying intervals from 3 days to 4 weeks. The livers were either removed and fixed in glutaraldehyde and osmium tetroxide or fixed in glutaraldehyde, incubated in a diaminobenzidine (DAB) medium, postfixed, embedded in Epon, and sectioned. Other tissues were incubated in Eagle's MEM containing either [P3H-thymidine or [3H]uridine, fixed, embedded in Epon, sectioned, and radioautographed. Specimens were observed in a Hitachi H-700 electron microscope. The number of peroxisomes showing DAB reactivity increased in DEHP-fed animals as compared with normal controls. In radioautograms of normal rats labelled with [3H]thymidine, no silver grains were observed, whereas grains were observed overt some nuclei, mitochondria and peroxisomes of DEHP-fed animals. In contrast, radioautograms of tissue labelled with [3H]uridine revealed a few grains in nuclei and mitochondria or endoplasmic reticulum of normal rats, although grains appeared in nuclei, mitochondria, endoplasmic reticulum and peroxisomes of DEHP-fed animals more frequently. From these results, it is concluded that [3H]thymidine and [3H]uridine were incorporated in the proliferating peroxisomes, suggesting that nucleic acid synthesis had taken place.