Increased survival of rats bearing Morris hepatoma 7800 after induction of hypothyroidism

The survival of Buffalo rats brearing Morris Hepatoma 7800 was increased significantly (23 to 31%) after induction of hypothyroidism by propylthiouracil (PTU) (0.1% in Purina rat chow) or 131I. The concentration of PTU used was in the optimal range as 0.03% PTU was less effective than 0.1%, while 0.4% PTU appeared to be toxic. Exogenous thyroxine (8 microgram/kg body weight) reversed the effects of PTU and actually shortened survival. Because food consumption and body weights of hypothyroid rats were decreased, the survival of pair-fed controls was studied and found to be the same as in untreated controls. We conclude that the hypothyroid state increases the survival of rats bearing Morris Hepatoma 7800. We have not yet been able to define any anatomical or biochemical parameters which may be responsible for this effect.