Secretion of haem by hepatic parenchymal cells.

Hepatic parenchymal cells in primary culture, and also the intact perfused liver, secrete newly synthesized haem into extracellular fluids. In cultures incubated with the haem precursor delta-amino[4-14C]laevulinate, labelled haem was formed at a linear rate for at least 8 h, and 10-20% of the total labelled haem was present in the culture medium. The appearance of labelled extracellular haem was proportional both to the concentration of labelled precursor offered to the cells and to the time of incubation. Similar results were obtained when [2-14C]glycine was added as haem precursor. Studies with the isolated perfused liver indicated that newly synthesized haem is secreted also by the intact liver. Approximately equal amounts of haem appeared in the bile and in perfusate. The findings are discussed in relation to the pathogenesis of symptoms in the hereditary hepatic porphyrias.