Effect of growth hormone on bone: Bone mineral density, trabecular bone volume, and alkaline phosphatase improve or are restored in the dwarf rat treated with growth hormone

Studies were performed to determine whether serum total alkaline phosphatase (SAP), an index of bone formation; body weight; total body bone mineral density (BMD), measured by dual-energy X-ray absorptiometry; and tibial trabecular bone volume (TBV), measured by histomorphometry, are reduced in 2-week-old female sexually immature Lewis dwarf (dw/dw) rats (DW-CT, n = 9) with isolated growth hormone (GH) deficiency and, if so, whether recombinant human GH (rhGH), 200 μg/day subcutaneously for 4 weeks (DW-GH, n = 7), restores them. Studies were also performed to determine if 30% dietary restriction in 2-week-old female Lewis rats (LW-DR, n = 11) alters SAP, body weight, total BMD, or TBV compared with pair-fed controls (LW-CT, n = 7) given an ad libitum diet. Mean SAP (91 ± 5 versus 109 ± 5 U/l), body weight (102 ± 11 versus 140 ± 10 g), total BMD (88.5 ± 03 versus 101.4 ± 2.0 mg/cm2), and TBV (19.0 ± 1.0 versus 27.0 ± 1.4%) were significantly lower in DW-CT than in LW-CT animals, p < 0.05. In DW-GH, rhGH significantly increased mean SAP (130 ± 7 U/l), body weight (133 ± 10 g), total BMD (92.7 ± 13), and TBV (24.0 ± 1.9) compared with DW-CT animals. Compared with LW-CT rats, mean body weight and TBV were not different, but mean SAP was significantly higher (p < 0.01) and mean total BMD was significantly lower (p < 0.003) in DW-GH rats. In LW-DR compared with LW-CT animals, dietary restriction significantly reduced mean body weight (p < 0.05) but did not alter mean SAP, total BMD, or TBV. Thus, body weight, SAP, total BMD, and TBV were lower in DW-CT than in LW-CT rats. In the dose administered, SAP is markedly increased and reductions in body weight, total BMD, and TBV are completely or partially restored by treatment with rhGH in young female rats caused by isolated GH deficiency. Dietary restriction in young female rats with intact secretion of GH prevents weight gain but does not alter SAP, total BMD, or TBV compared with animals fed ad libitum.