Feed intake and protein skeletal muscle in growing mice treated with growth hormone: time course effects

The exogenous recombinant human growth hormone (rhGH) administration on gas trocnemius muscle growth performance and its contribution to body growth of male and female BALB/c mice fed a 12 % protein diet from 25 to 50 days of age, as well as the mechanism of utilization of feed intake to the lean mus cle deposition were studied. Male and female weaning mice (21 days of age) were injected subcutaneously for 29 days with rhGH (74 ng.g-1) or saline ve hicle (control). Feed intake and body weight (BW)were measured daily. At 25 , 30, 35, 40, 45 and 50 days of age twenty mice were killed by cervical dis location and the gastrocnemius muscle was isolated, weighed and the protein content was measured. The rhGH administration caused a biphasic response o f BW and muscle growth as a consequence of age-specific feed intake changes . The initial feed intake fall induced the allometric proportion decreases in both muscle growth versus body growth and protein muscle versus muscle g rowth. That effect was due to ineffient utilization of energy and protein i ntake on protein muscle store. Later on, the self-controlled increase of fe ed intake leads to the recovery of muscle weight to control values, through nutrient partitioning toward non protein tissue showing a compensatory mus cle growth. This suggests that a higher dietary protein level should be nec essary for promoting the protein anabolic effect of GH during weaning.