Indices of skeletal muscle growth in lean and obese Zucker rats

Skeletal muscle growth was studied in gastrocnemius muscle of lean and obese ad libitum or pair-fed Zucker rats. Skeletal muscle cellularity was determined by DNA, RNA and protein analysis. The length and weight of the tibia and femur were determined. All rats were killed at 15 weeks of age. Lean rats had heavier gastrocnemius, total DNA and total protein than either the ad libitum (ALO) or pair-fed (PFO) obese rats. Lean rats had longer and heavier tibias. Femur length was greater in lean animals while femur weight did not differ between lean and ALO groups. Both had heavier femur than the PFO rats. Comparison of the obese rats revealed that the ALO rats had greater gastrocnemius weight, total DNA and total protein than the PFO group. Total RNA was not different between the lean and ALO group. Comparison of tibias and femurs showed the ALO rats to have longer and heavier bones than the PFO rats. In summary, there are marked differences in the bones of the hindlimb and the cellularity of the gastrocnemius muscle between lean and obese Zucker rats. The differences were accentuated by pair feeding the obese rat.