Bilateral asymmetry in bone weight at various skeletal sites of the rat.

BACKGROUND

Morphological and functional asymmetry in the limbs has generally been regarded as a human characteristic that is of genetic or of both genetic and environmental origin. The aim of this study was to determine the presence of lateral dominance in bone weight of the forelimb of the rat.

METHODS

Wistar rats (77) were used, 45 controls and 32 experimental animals, implanted with a steel weight subcutaneously under the right forelimb. Bones examined for bilateral asymmetry in bone weight were the mandibula, the bones of fore- and hindlimbs, calcaneus, and talus of the tarsus. The weight of each dry bone was measured to the nearest milligram.

RESULTS

Significant bilateral asymmetry in the forelimb was evident in male and female rats, with the left side having more bone mass than the right. Bilateral differences were more pronounced in the females than the male rats. Greater asymmetry was evident in the experimental group compared to the control rats.

CONCLUSIONS

These findings demonstrate that asymmetry is present not only in humans, but also in lower animals such as rats. Greater asymmetry in the experimental rat group is indicative of the influence of environmental factors or physical stress on asymmetry. We conclude that genetics might control the development of asymmetry, but physical stress may alter the functional expression of the asymmetry.