Response and adaptation of beagle dogs to hypergravity.

Eight male Beagle dogs, five months old, were centrifuged for three months at progressively increasing loads ranging from 1.5 g to 2.5 g on a 7.9 m radius centrifuge. Dogs were maintained on the centrifuge, which was run almost continuously, by employing a special designed automated waste disposal and life support system. Heart rate and deep body temperature were monitored continuously by implant biotelemetry. Initially, centrifuged dogs showed transient decreases in heart rate and body temperature along with changes in their diurnal rhythm patterns. Compared with normal gravity controls, exposed dogs showed a slower growth rate and a reduced amount of body fat. Blood protein, total lipids, cholesterol, calcium, packed cell volume, red blood cell count, and hemoglobin were also decreased significantly. Absolute weights of the leg bones of centrifuged dogs were significantly greater than controls. Photon absorptiometry revealed significant density increases in selective regions of the femur and humerus of centrifuged dogs. In spite of the various changes noted, results from this and other studies affirm the view that dogs can tolerate and adapt to sustained loads as high as 2.5 g without serious impairment of their body structure and function.