Liver explants from 20-day-old foetuses cultured for 48h in the absence of serum released 70% of their total soluble protein content into the medium. In the presence of serum this loss still amounted to 60%. The concentration of total particulate protein remained unchanged but there was some translocation of mitochondrial enzymes to the cytosol, and enzymes expected to increase during this stage of development failed to do so. The addition of cortisol plus glucagon (to serum-containing media) did not decrease the loss of total soluble protein from the explants but induced considerable tyrosine aminotransferase activity which was not released into the medium. The observations suggest that under the usual culture conditions a minority of the cells retain their functional integrity. The extent of deterioration, not reflected in histologically visible necrosis or cell damage, can be conveniently monitored by the malate dehydrogenase activity released to the medium.
