Biology: The Puzzle of Aging

When it leaves the ocean to swim up the rivers of the Northwest and spawn, the Pacific salmon is lithe and healthy. As little as two weeks later, it degenerates into an aged, colorless and almost lifeless fish. Its flesh wastes away, bones soften, and skin peels off. The secretion of mucous material that keeps scales healthy suddenly stops, and the fish falls prey to fungus infections. Tiny parasitic worms multiply and spread through the fish’s body; some glands run wild, others cease functioning.

What causes this piscatorial version of The Picture of Dorian Gray? Now, after studying the salmon for six weeks during a Pacific voyage aboard the oceanographic ship Alpha Helix, 40 scientists and doctors have returned to the U.S. with some provocative insights into the aging process.

Out of Fuel. Aboard the Alpha Helix, Biochemist Eberhard Trams of the National Institutes of Health discovered that the brain’s control of the pituitary gland was a major factor in the sudden aging of the salmon. As the fish enters fresh water, he found, the pituitary quickly grows to more than twice its normal size, and the central nervous system fails to maintain control. The gland then triggers a metabolic speedup that burns away practically all of the fat in the salmon’s body. Biochemist Andrew Benson, associate director of the Scripps Institution of Oceanography, explains: “It is as though all the glands were programmed to cause the combustion of fat simultaneously so that the whole machine runs out of fuel.”

Another effect of the fresh water, says Benson, is to stimulate the production of a hormone that causes calcium to dissolve out of the bones. The bloodstream is thus supplied with calcium that is no longer available from the calcium carbonate in ocean water—but the cost is high. The salmon’s bones soften and virtually dissolve.

Clogging the Arteries. Both the pituitary gland changes and the loss of bone calcium in salmon are also familiar symptoms of aging in humans. “But in the fish,” says Biochemist Trams, “the gland goes to hell in two weeks, a process that takes some 20 to 40 years in man.” Thus the salmon makes an “ideal laboratory tool” for the investigation of geriatric ailments.

The salmon, Benson suggests, may eventually provide researchers with clues to methods for lessening the ravages of aging and with new knowledge of arteriosclerosis, which is caused at least in part by high concentrations of cholesterol in the bloodstream. In the ocean, the salmon has from five to ten times as much cholesterol in its bloodstream as a human can tolerate. “If we find out how the salmon manages to survive with this much cholesterol,” says Benson, “perhaps we can help humans survive also.”