43. Effects of Clinostat-microgravity and Heavy Particle Radiation on Bone and Calcium Metabolism in Rats

Satoshi Fukuda and Haruzo Iida

Keywords: clinostat-microgravity, heavy particle beam, bone histomorphometry, bone mineral density, rats

We have previously developed a clinostat-microgravity rat model as a new ground-based model for clarifying the changes that occur in systemic bone and calcium metabolism in the space environment. The aims of the present study were to examine the effects of (1) a 2-week period of clinostat-microgravity, which is the average period of a space flight, so that the results could be compared with those of previous reports; (2) exposure to heavy particle radiation, a component of cosmic rays; and (3) the combination of clinostat-microgravity and radiation on bone and calcium metabolism in rats. Bone mineral density, histomorphometric values, the breaking force of bone, intestinal calcium absorption, urinary calcium excretion, calcium regulating hormones (PTH and BGP), and weights of adrenal gland and skeletal muscles were measured. The clinostat-microgravity model produced a low bone turnover with decreases in bone formation and resorption, trabecular BMD, intestinal calcium absorption, and BGP concentration, and increase in PTH concentration, but other data remained unchanged or actually increased. Exposure to heavy particle radiation inhibited bone metabolism, e.g. lack of bone labels, with doses of 1.25-5.0 Gy as well as changes in the bones, intestinal calcium absorption, urinary calcium excretion, PTH and BGP concentrations. With a combination of both clinostat-microgravity and radiation, such changes tended to be more pronounced, and noticeable findings were seen as the bone labels in the groups irradiated with 1.25 and 2.5 Gy, but no bone label in the group irradiated with 5.0 Gy. Based on the gathered data, the utility of the clinostat-mirogravity model, the effects of the short-term experiment, the exposure to radiation, and the combination of clinostat-microgravity and radiation can be discussed.

Publications:
Fukuda S. and Iida H.: J. Jpn. Soc. Bone Morphom, 9, 35-44, 1999.