The lack of a "pleiotypic response' in hepatocyte proliferation induced in the rat by 3,5,3'-triiodothyronine.

Early morphological and biochemical alterations in proliferatively stimulated liver tissue obtained from 3,5,3'-triiodo-L-thyronine-treated rats were compared to those occurring in the liver remnant of 70% hepatectomized animals, and to controls. Subjecting photographic enlargements of histological slides prepared from these liver tissues to computer-assisted analyses, hepatocyte nuclear and nucleolar volumes were shown to be virtually identical in control and hormone-treated preparations through the first 24 hours after treatment, but significantly different from tissues obtained from partially hepatectomized animals, In vitro estimations of hepatic nuclear RNA polymerase activities early after treatment were also shown to be similar when comparing the hormone- and the saline-treated rats. Estimated by either 3H-orotic acid or 3H-leucine incorporation, the early accumulation of hepatic RNA and liver and serum proteins, significantly enhanced by 70% hepatectomy, were found similar in triiodothyronine-injected and control animals at least through the first 6 h after treatment; hormone administration appeared to cause slight enhancements in these parameters at later prereplicative times. While pharmacological doses (200 micrograms/100g) of the thyroid hormone induce a strong proliferative response in rat liver tissue, only minor prereplicative alterations appear to be elicited in the hepatocytes. This hepatic model offers an important potential tool to investigations aimed at understanding proliferative controls in mammalian liver cells.