Gravity, More or Less

One way to longer life may be higher gravity--at least for rats. That is the "very tentative suggestion" of experiments performed by NASA Physiologist Jiro Oyama, who has been raising mice and rats under artificial gravities created by centrifuges at Ames Research Center in California. Whirling on an 8 1/2-ft. centrifuge, two female rats survived for 47 months, a year longer than their normal three-year life span.

The answer to their longevity may well be the depletion of body fat. In other centrifuge experiments, Oyama subjected weanling rats (three to four weeks old) to 4.7 G. for three to six months. Within 24 hours after he returned them to normal gravity by removing them from the centrifuge, the animals gained approximately 10% in body mass. Conversely, weanling rats raised under normal gravity lost about 10% of their mass--much of it in body fat--within 24 hours after being placed in the higher artificial gravity of a centrifuge. To probe the fat-depletion phenomenon further, Oyama plans to induce arteriosclerosis in rabbits by feeding them high-cholesterol diets and then putting them in a centrifuge to determine if the disease is lessened under conditions of higher gravity.

Continuous Spin. Oyama's longevity findings were an unexpected byproduct of experiments to learn something about the effects of prolonged space travel upon astronauts, who will soon be spending months in orbit under conditions of weightlessness, and exploring the moon, which has only one-sixth of earth's gravity. Reduced gravity over so long a period of time, space scientists fear, may produce effects that did not emerge during the relatively short manned space flights made to date.

To gain insight into possibly harmful effects, Oyama has been raising mice and rats in 4-and 8 1/2-ft. radius centrifuges that create artificial gravities from twice to 4.7 times normal and spin continuously except for brief intervals when they are shut down to clean cages and replenish food supplies. When the test animals are finally removed and returned to the normal gravity of earth, their experience is roughly equivalent to that of astronauts suddenly subjected to weightlessness or to a fraction of terrestrial gravity.

Expanding the gravity studies, Oyama and NASA Biologist William Platt have begun to use a new 26-ft.-radius centrifuge that can be supplied with food and cleansed of waste while it is running. On it, generations of rodents can be born and spend their entire lives under uninterrupted higher G. loads. From the responses of test animals--eventually including primates--Oyama hopes to predict the effects on astronauts of space trips that last for months and even years.

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