[Control of multiplication and polyploidy of rat hepatocytes : A study of the perturbations of physiological regulation induced by injection of irritants].

The injection of irritating substances of various chemical nature disturbs the mechanisms regulating the multiplication of rat hepatocytes.The reaction of baby rats is intense and reproducible. It results, 15 hours after the injection, in an increase of the number of cells entering the S phase, so that practically all the divisions which would normally have been scattered over 36 hours are initiated within 2 hours. This burst of synchronized mitosis corresponding to a 36 hours advance in the hepatic growth is followed by a decrease of mitoses due to a feed-back inhibition.The reaction of older rats brings to evidence a permanent inhibitory mechanism that results in a less regular and intensive response.The production of binucleated and polyploÏd hepatocytes seems to be correlated to this inhibitory mechanism.The regularity and sensivity of the baby rat reactions make them a choice material for the study of hepatic growth.