The European Journal of Orthodontics Advance Access published online on February 28, 2008
The European Journal of Orthodontics, doi:10.1093/ejo/cjm101
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Timing effects of growth hormone supplementation on rat craniofacial growth
* Private Practice, Meridian, Idaho, USA
** Department of Orthodontics, Baylor College of Dentistry, Texas A&M University System Health Sciences Center, USA
*** Department of Biomedical Sciences, Baylor College of Dentistry, Texas A&M University System Health Sciences Center, USA
Address for correspondence Robert J. Hinton, Department of Biomedical Sciences, Baylor College of Dentistry, 3302 Gaston Avenue, Dallas TX 75246, USA. E-mail: bhinton{at}bcd.tamhsc.edu
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Abstract |
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Growth hormone (GH) supplementation has become a popular treatment approach for GH normal children with short stature. To investigate how the timing of GH supplementation affects the growth of the craniofacial region, three groups of GH-normal, 28-day-old female Wistar rats were examined over 4 weeks: the early group (n = 10) received two daily injections of rhGH (2 mg/kg/day) from days 1 to 28, the late group (n = 10) received two daily saline injections from days 1 to 14 (Phase I) followed by two daily injections of rhGH from days 14 to 28 (Phase II), and the control group (n = 12) received two daily saline injections from days 1 to 28. Lateral cephalometric, forelimb and hindlimb radiographs obtained weekly were scanned, standardized points digitized, and distances were measured using the Viewbox® software. Growth curves between groups were compared using multilevel iterative generalized least squares curve fitting procedures.
Supplementation during Phase I in the early group produced significant treatment effects in cranial and cranial base, midface, posterior corpus, and limb lengths which varied inversely with relative maturity (percentage growth completed at the start of the study). During Phase II, GH supplementation in the early and late groups showed treatment effects as above and additional viscerocranial and mandibular measurements, but these effects were unrelated to the relative maturity of the variables. These latter results are at variance with earlier findings in GH-deficient rats, raising the possibility that that GH-normal rats may not respond to GH supplementation in a similar fashion to GH-deficient rats.