Background: The mechanism of growth hormone (GH) effects on growth plate (GP) and its chondrocytes is of utmost importance, thus we have investigated the microstructure of proximal tibial GP of rabbits with designed-based stereological methods.

Material and methods: In this experimental study, the tissue came from a study into longitudinal growth using minipumps surgically implanted into the right upper tibial GP of 9 weeks old rabbits, administering GH at 10 and 100 μ g/day for a period of 21 days. Saline only administered and non-operated groups served as controls. The following stereological parameters were investigated: GP volume and height chondrocyte volume, surface and number densities. These direct measurements lead to estimate of chondrocyte total volume, surface and number mean chondrocyte volume and surface in the number-weighted distribution. Data were analyzed using t-test and single factor ANOVA, then if there was any significant difference, Dunnett’s multiple comparison test was performed.

Results: No significant differences were found between the right and left tibial and saline and control groups in the total quantities. The GP volume and height and chondrocyte total volume showed no significant differences between the treatment and control groups.

Conclusion: GH acts on rabbit proximal tibial GP by inducing chondrocyte hyperplasia but not hypertrophy. The operative procedure of implanting a minipump had no detectable effect on any of the parameters measured. GH had an effect on the local cytostructure of the GP on the treated side.