A Dec. 31 letter from the People for the Ethical Treatment of Animals asked Frist to make amends by pressing for reforms that would replace old-style tests where animals are subjected to painful and sometimes deadly procedures with newer, more humane approaches. They also requested that he help fund research to find non-animal alternatives.
Frist acknowledged in a 1989 book that he routinely killed cats while an ambitious medical student at Harvard Medical School in the 1970s. His office said it had no record on how many cats died. Frist disclosed that he went to animal shelters and pretended to adopt the cats, telling shelter personnel he intended to keep them as pets. Instead he used them to sharpen his surgical skills, killing them in the process.
The newly elected leader of the Senate Republicans revealed the practice in his book "Transplant: A Heart Surgeon's Account of the Life-and-Death Dramas of the New Medicine."
"It was a heinous and dishonest thing to do," Frist wrote, in a passage quoted by The Boston Globe. On Tuesday, Frist's press aide, Nick Smith, told United Press International that "Senator Frist denounces the activities that he did while he was in medical school -- as he has done before."
It is not clear if Frist's actions were illegal. Many states ban shelters from knowingly letting their animals be taken for such purposes.
Massachusetts put such a ban in place in 1983. Frist was a student in the Boston area from 1974 to 1978. A total of 14 states have passed such laws. Four states -- Iowa, Minnesota, Utah and Oklahoma -- still have laws that allow labs to demand the release of animals for experimental use.
But such regulations, called pound seizure laws, only govern the actions of the shelters.
"The pound seizure law probably would not apply there because the shelter did not intentionally sell the animal to him for this purpose," said Debora Bresch, a lawyer and a lobbyist for the American Society for the Prevention of Cruelty to Animals.
"They thought they were adopting the animal out to him," said Bresch. "What he did was fraudulent and probably was illegal."
"It would probably would be considered cruel back even then," added Stephen Musso, senior vice president and chief of operations of ASPCA.
Though Musso said he personally had not heard about the Frist incident, he told UPI, "We wouldn't want to see anybody taking an animal out of an animal shelter and doing anything with it -- first of all that would be harmful; second of all, different than the intentions that they gave to the people at that shelter or humane organization."
Attitudes toward animal experimentation have shifted, said Gary Patronek, director of the Tufts Center for Animals and Public Policy in North Grafton, Mass.
"The fact that laws have passed prohibiting the practice of pound seizure in 14 states is evidence of the fact that society's attitudes have changed," Patronek told UPI. "The laws reflect the attitudes. If there isn't a broad social consensus about something, then typically the laws don't change."
The demographics have changed also. By the end of 2000, a total of 34 percent of American households had at least one cat -- a sharp rise of 8 percent in only two years. The American Pet Products Manufacturers Association also said in their 2001-2002 National Pet Owner Survey that 39 percent of all U.S. households owned at least one dog in 2000, about the same percentage as in 1998.
Though Frist's practice has been known for 11 years, the matter appears to be gathering new attention since his election as Senate majority leader. E-mail with copies of news articles mentioning the incident are bouncing around the Internet, said Bresch.
One Frist supporter said the senator's opponents are fueling the interest in the issue.
"What is happening here is that people are doing profiles of the senator, and they are desperate to find something wrong with him and to come up with something bad in his past," he pointed out.
Whether Frist will come to the aid of animal legislative causes remains to be seen. His spokesman said they had not seen the PETA letter and therefore would not comment on it.
PETA, normally more combative and high-profile, took a somewhat restrained tone in its letter. There was no mistaking PETA's opinion, however, as the organization asked Frist to make an effort on the animals' behalf.
"There could be no better way of making some small amends to those animals whose trust you betrayed when you took them from shelters," the letter said.
(With reporting by Nicholas M. Horrock in Washington)
Notable deaths of 2014 [PHOTOS]