Alterations in the mechanical properties and composition of skin in human growth hormone transgenic mice.

Growth hormone is known to stimulate connective tissue, but the degree to which it influences skin biomechanical properties is unclear. This study tested the hypothesis that human growth hormone transgene expression changes the material properties and structural composition of adult mouse skin. Fracture toughness and elastic modulus were measured on freshly dissected dorsal skin and fixed samples were analyzed histologically. Transgenics had higher elastic moduli than their sex-matched non transgenic littermates, and male transgenics demonstrated increased fracture toughness. Male transgenics also had thicker skin than controls with a selectively increased dermis. In contrast, female transgenics had thinner skin than controls due to a reduced hypodermis. Biomechanical and histological variables were strongly correlated. Significant sex differences were present in nearly all comparisons indicating a dimorphic response to growth hormone in the skin. These data demonstrate that constant low-level growth hormone expression in marrow differentially affects skin layer thickness and concomitantly alters its biomechanical properties.