By David N. Leff

A few years ago, transplant surgeon Thomas Starzl, who pioneered liver transplantation, engrafted baboon livers into two human recipients at the University of Pittsburgh. Within a week, the donor organs had grown to the normal size of their hosts' livers.

By the opposite token, when a Great Dane's liver is transplanted into a beagle, it quickly shrinks down to beagle size.

And if surgery or trauma cuts a large slice out of a person's liver, the missing lobes promptly grow back.

All of which means that the hepatic organ is the human body's champion regenerator.

Legions of hepatologists and cell biologists are busily scrutinizing the liver's puzzling ability to grow itself back. They are beginning to discover its secrets, and hope to apply them to other, more static organs, perhaps even to limbs.

After all, when the lowly newt, or salamander, loses a leg, a replacement comes along spontaneously to replace it.

In the current issue of Science, dated April 4, 1997, two pathologists at the University of Pittsburgh update research into "Liver regeneration."

"A single hepatocyte [liver cell]," they write, "can expand through a minimal number of 34 cell divisions, giving rise to 1.7 billion cells." They go on to calculate "that a single rat hepatocyte . . . has enough clonogenic capacity to generate about 50 rat livers.

"Perhaps even more remarkable than the capacity of hepatocytes to proliferate," they add, "is that they do so while simultaneously performing all essential functions needed for homeostasis."

They describe an experiment in which two rats are hooked up to a single common parabiotic bloodstream and one has its liver totally excised. It grows back intact.

In myth, if not in fact, as the Pittsburgh authors recall, hepatectomy and liver regeneration go back to the ancient Greek gods. When Prometheus stole their fire, Zeus had him chained to a rock and sent an eagle to eat his liver every day. It regenerated overnight, "thus providing the eagle with eternal food and Prometheus with eternal torture." *