Unusual mitochondria in the hepatocytes of rats treated with a vitamin B12 analogue

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Abstract
Adult male rats were administered hydroxy‐cobalamin (c‐lactam) (HCCL), a vitamin B12 analogue, by means of osmotic mini‐pumps. The metabolic effects of HCCL, are similar to those produced by simple dietary deficiency of vitamin B12 (Frenkel et al., 1976), but the morphological alterations in hepatic mitochondria are quite different in the two treatments. In HCCL‐treated animals, hepatic mitochondria showed significant increases in number. In one rat, the hepatic mitochondria frequently had a single, elongated, circumferentially‐oriented crista, with the inner compartment being occupied by a greatly augmented matrix. Such organelles appeared to be capable of division, as indicated by medially‐partitioned forms. Numerous hooded mitochondria were present in the hepatic cells of the same animal. Almost every mitochondrion of whatever morphology was partially or completely shrouded by a cistern of rough endoplasmic reticulum. These mitochondrial morphological changes may be related to the chronic metabolic changes in this animal model of methylmalonic aciduria.