A Strategy for Research in Space Biology and Medicine in the New Century by Committee on Space Biology & Medicine

Author:Committee on Space Biology & Medicine
Language: eng
Format: epub
Tags: Space and Aeronautics : Policy, Reviews and Evaluations
Publisher: NATIONAL ACADEMY PRESS
Published: 1998-09-22T00:00:00+00:00

9

Endocrinology

Introduction

The endocrine, nervous, and immune systems regulate the human response to spaceflight and the readjustment processes that follow landing. There is a multidirectional flow of information among these three systems, which together are responsible for maintaining homeostasis and reestablishing homeostasis if it is perturbed.1 2 3 4 5 6 Quite apart from the intrinsic scientific interest of the underlying mechanisms, a basic knowledge and understanding of the effects of spaceflight on the endocrine and neuroendocrine systems are essential to the rational development of countermeasures.

Aspects of endocrine influence on specific organ systems are addressed in several chapters of this report. This chapter stresses integrative homeostatic functions of the endocrine and neuroendocrine systems. The principal spaceflight responses with a significant endocrine contribution are fluid shifts, perturbation of the circadian rhythms, loss of red blood cell mass, possible changes in the immune system, loss of bone and muscle, and maintenance of energy balance. The last three are chronic responses, whereas fluid shifts occur only after entry into a microgravity environment and again after return to Earth. Whether perturbations of circadian rhythms and loss of red blood cell mass are short- or long-term problems is not known.

In the space station era, systems physiology research will shift from the investigation of the acute responses to spaceflight to the long-term effects.7 The former are associated with large, immediate changes in certain hormones. Thus, the change in blood volume, red cell mass, and the associated fluid shifts are acute responses to the novel environment, with appropriately large and immediate changes in hormone levels such as ADH (antidiuretic hormone, or vasopressin), aldosterone, and norepinephrine. What is needed is a focus on the problems of long-term spaceflight, specifically calcium loss from bone, muscle atrophy, energy balance, and the possible perturbation of circadian rhythms.

Many biological investigations involve endocrine measurements. Such measurements are often not the primary focus of the study but are necessary to identify the perturbation mechanism that is the actual subject of investigation. Studies of bone calcium losses are an example. In contrast with other systems such as fluid and electrolyte balance and circadian rhythms, and for some muscle experiments, endocrine measurements are the primary focus of the study. Thus many of the chapters in this report refer to making endocrine measurements.

In the past, postflight measurements have been used to extrapolate back to the in-flight situation. Postflight hormone measurements are not an adequate substitute for in-flight measurements because they measure only the postflight situation. The half-life of most hormones in the plasma is too short—usually on the order of minutes or less—to have any bearing on any situation except the one that exists at the time the sample was collected.

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