Influence of Plasma Hormone Levels on Various Stimulant-Induced Hepatic DNA Synthesis in Carbon Tetrachloride-Intoxicated Rats

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Abstract
The effects of insulin, glucagon, isoproterenol and carbachol on the regeneration of injured liver were investigated in rats treated with CCl4. These agents effectively potentiated hepatic DNA synthesis in rats both at 48 and at 72 h after CCl4 intoxication. The maximal stimulatory effects of the agents on the synthesis coincided in time with the peak of elevation in basal DNA synthesis following the intoxication. Plasma levels of insulin and triiodothyronine were decreased before the elevation of basal DNA synthesis in CCl4-treated rats. The possible relationship of these changes in plasma hormones to the potentiated effects of the agents on DNA synthesis was examined in rats treated with streptozotocin (STZ) or methylthiouracil (MTU). The agents caused no potentiation in STZ-treated rats. On the other hand, in MTU-treated rats, isoproterenol and carbachol significantly stimulated DNA synthesis, but this was not the case with insulin and glucagon. The pancreatic hormonal, .beta.-adrenergic and cholinergic stimulations apparently play positive roles in regulating liver regeneration after CCl4 intoxication. The hypothyroid state developed in CCl4-treated rats may provide favorable conditions for the stimulation of DNA synthesis by isoproterenol and carbachol. Insulin deficiency does not seem to contribute to potentiations in the regenerative responses of the injured liver.