Fine structure of rat liver during chronic intoxication with two heterocyclic N-nitrosamines: N-nitrosopiperidine and the non-carcinogen, 2,2',6,6'-tetramethyl-N-nitrosopiperidine.

A comparative fine structural investigation was carried out on the long-term effects on rat liver of chronic exposure to the carcinogen, N-nitrosopiperidine (NPIP) and its non-carcinogenic derivative, 2,2',6,6'-tetramethyl-N-nitrosopiperidine. Some morphological alterations apparently related to drug metabolism and toxicity were common to both compounds. Others, notably that involving the rough ER, were specific to NPIP and resembled those that are induced by other hepatocarcinogens and are characteristic of hepatic cell tumour. It is suggested that the rough ER lesion is associated with initiation and provides a morphological "marker" for the induction of liver neoplasia.