The recent transfer of a baboon's heart into the body of a human infant dramatizes how far medical science is pushing the frontiers of organ transplantation - and the thicket of questions this development poses.
The unusual transplant by doctors at the Loma Linda University Medical Center in California is seen by them as opening the way to a much-needed new source of organs for humans.
If it succeeds (last week ''Baby Fae'' became the longest survivor of such a transfer), a few enthusiasts in the medical community envisage that it will usher in a new era in transplantation from animals to human beings.
But the experimental operation is also stirring deep-seated moral, ethical, and social questions about where - and how fast - doctors should be going in the rapidly emerging field of organ transplantation. Many of the issues go well beyond this case, and will continue to surface no matter what its ultimate outcome.
Animal-to-human transplants, though novel, are not unique. Four prior attempts have been made over the years to use baboon hearts in humans (anatomically their organs are virtually the same). All ended in the deaths of the patients within a few days. Baby Fae is the youngest person on whom such a technique has been tried.
Many in the medical community believe that the science of cross-species transplants hasn't advanced to the point where it should be attempted on humans. They believe there are still too many risks involved.
''There really is no ethical basis for using baboon hearts in a child at all, '' asserts George Annas, professor of health law at Boston University School of Medicine. ''What is going on here? Are we getting back to the old days when doctors just experimented (on people)?''
Some draw parallels to the controversial and ultimately fatal implant of the world's first permanent artificial heart in Barney Clark in 1982. In that case, though, Dr. Clark agreed to the operation knowing the risks. In the Baby Fae case, consent was from the parents.
The doctor heading the surgical team, Leonard L. Bailey, has spent seven years doing transplants between animals to prepare for the operation. The surgical team used a new immunity-suppressing drug in their experiment with Baby Fae that is credited for recent improvement in the success of transplants in general. The drug is said to reduce the likelihood of the body's rejecting the donor heart - a key problem in such procedures - but it can damage other organs, doctors warn.
Of concern to some in the medical community, too, is whether there was a human heart available that could have been used for the transplant. Whether there was or not, doctors involved in the experiment have made clear that their research is aimed at animal-to-human transplants. Baby Fae was the first of what Loma Linda hospital officials hope will be five baboon-to-infant heart transfers they will do.
The experiment, in fact, points up some of the problems facing organ transplantion in general. The field has been heralded as one of American medicine's compelling new achievements. But there are not enough human organs available to meet medical demand. There were 172 heart, 163 liver, and more than 6,000 kidney transplants performed in the United States last year. These numbers are expected to jump dramatically in the near future.
Federal legislation that was signed into law last month seeks to improve the current patchwork system of retrieving organs. States and localities have also been grappling with the issue. There is strong sentiment, moreover, for both the federal government and private insur-ance companies to pay for costly transplant surgery. But this has raised thorny issues of its own: Some health officials, for instance, question the idea of promoting trans-plants at a time when more basic health-care programs are short of funds.
The Baby Fae case, for its part, hasn't set off any economic debates over use of scarce medical resources, but it has become a lightning rod for the enduring clash between animal-rights groups and scientists. More fundamentally, it has also stirred some theological concerns about the basic identity of man and whether various animal parts should be used in human beings at all. Such a practice isn't new. For some time now, doctors have been using some animal parts routinely in human surgery. Some heart valves come from pigs, for instance.
But putting an animal organ as symbolic as the heart in a human is seen by some as violating the uniqueness of the human species. ''What is worrying a lot of people is: What does putting an animal heart in a person do to our understanding of a human?'' notes Douglas MacDonald, professor of philosophy at Furman University in South Carolina. If doctors start putting animal parts in people, he adds, the question arises: What constitutes ''our humanity? Is it just a physical, biological body?''
Doctors involved in the case have said they see the heart as a pump.
Whatever the outcome of the Baby Fae experiment, similar issues are likely to keep arising. Dr. Ronald Bayer, an associate for policy studies at the Hastings Center, a New York institution devoted to the study of bioethical issues, reminds us that, in the past, the impact of medical science was limited by the knowledge available. Today, technical advances are increasingly generating tough choices that demand more public involvement.
''Ultimately, we are going to have to face the difficult moral, economic, and political choices about which life-saving human technology we want to pursue,'' he says.