VERTEBRAL GROWTH DISTURBANCE IN RAPIDLY GROWING RATS DURING 14 DAYS OF SPACEFLIGHT

The effect of 14 days of spaceflight on tile vertebrae of rapidly grow ing rats was studied. The hardness of the vertebrae was measured with a Knoop microhardness tester and bone mineral density was measured Fro m X-ray photographs. Histomorphometric examination was performed with a microcomputer-aided system. No significant difference (P > 0.05) was observed between flight rats and ground controls with regard to mecha nical hardness or bone mineral density. However, histological examinat ion revealed irregular thickening of the endosteal surface of cortical bone in the flight rats, whereas it was uniform in the ground control s. The relative area of lamellar bone showed a significant cant reduct ion (P < 0.001) in the flight rats. These findings suggest that the st ructural disturbances were due to retardation of endosteal modeling an d remodeling. We conclude that delay of vertebral maturation can occur in rapidly growing rats after even short-term exposure to microgravit y.