Growth-hormone levels plummet in space.

Growth-hormone levels plummet in space

The earthly theater of evolution has undergone coutless scene changes since life first emerged, but gravity has never been absent.

Only in ht epast three decades of space flight have organisms spent prolonged periods beyond gravity's powerfl grasp. And biological business does not go on as usual in the microgravity setting. Atronauts and test animals have returned to Earth with atrophied muscles, embrittled bones, depressed immune systems and other bodily changes.

Some of these problems may result from a decreased ability to secrete functioning growth hormone, suggests biochemist Wesley C. Hymer of Pennsylvania State University in State College. The pituitary-produced a hormone serves many roles, including regulating growth and metabolism.

In 1983, Hymer and Richard Grindeland of NASA's Ames Research Center in Mountain View, Calif., sent cultured rat pituitary cells into space aboard Space Lab 3. Two years later, they orbited five live rats abroad a space whuttle, In 1987 and 1989, they placed equal number of rats aboard Soviet Cosmoc Biosatellite missions.

Hymer, who als heads one of NASA's 16 Centers for the Commercial Development of Space presented the pooled results of these experiments this week at a meeting of the American Chemical Society in Washington, D.C.

Space-flown pituitary cells, tested soon after their return, produce as little as half as much active growth hormone as their Earth-bound counterparts, Hymer reports. Biochemical tests show that microgravity lead to smaller aggregates of growth-hormone molecules, possibly explaining the hormone's reduced ability to induce bone growth in physiological tests. A graduate student in his lab also discovered that standard immunoflorescence probes misleadingly indicate high hormone levels in the space-flown cells despite the hormoes, relative inactivity.

The rat finding may not bode well for long-duration space visits by humans, Hymer says. Still, he notes no one has demonstrated a link between the decline of active growth hormone in test cells and the loss of muscle and bone strength in astronauts. But if that link exists, studies like his might point toward drug strategies to compensate for space-induced hormone deficits, he says.

Moreover, diseases such as osteoporosis may involve similar growth-hormone-mediated processes under normal gravity conditions, Hymer speculates. If so, he says, space-flown rats and cell cultures could provide a model for drug companies seeking to test new treatments for earthly patients.