Intramuscular injection with botulinum toxin A (BTX) leads to a transient paralysis of the muscles, resulting in a rapid loss of muscle mass and function as well as rapid bone loss (disuse osteoporosis). The purpose of this study was to investigate the temporal development and the site specificity of BTX-induced immobilization on bone strength at five skeletal sites. Three-month-old rats (n = 108) were randomized into nine groups: one served as baseline, while four were injected with BTX and four with saline in the right hind-limb musculature. Animals were killed after 1, 2, 3, or 4 weeks. BTX-induced a significant loss of rectus femoris muscle mass (-61%) and muscle cell cross-sectional area (-59%) as well as bone strength at the femoral neck (-31%), femoral diaphysis (-6%), distal femoral metaphysis (-17%), proximal tibial metaphysis (-31%), and tibial diaphysis (-13%) after 4 weeks. Muscle atrophy occurred in parallel with the bone loss at the femoral neck and proximal tibia, whereas it occurred earlier than the bone loss at the other skeletal sites. At the proximal tibial metaphysis BTX significantly decreased BV/TV (-10%), trabecular thickness (-13%), and bone formation (MS/BS -25%, BFR/BS -50%) and increased osteoclast covered surfaces (+97%) after 4 weeks. In conclusion, BTX-induced a time-dependent loss of bone strength. Moreover, the loss of bone strength differed significantly at the five tested skeletal sites.

The aim was to assess the luminal cross-sectional area (CSA) and the passive elastic properties of the oesophageal body under luminal pressure loading in anaesthetized rabbits. Stepwise inflation of a luminal balloon, in which the CSA and pressure were measured by means of impedance planimetry and perfused low-compliance manometry, provided the distension stimulus. The parameters of elasticity were computed from steady state values of these measurements. The steady state pressure-CSA and pressure-radius relations were nonlinear. At the lowest and highest luminal pressure load of 1 and 10 kPa, the steady state CSAs were 39 ± 3 and 91 ± 4 mm², respectively. The circumferential tension-strain distribution was nonlinear and showed an exponential behaviour that fitted well to the function tension = a·e^b·stram. Differentiation of the function yielded the wall stiffness which also showed an exponential behaviour.

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