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There is a great need to further characterise the available animal models for postmenopausal osteoporosis, for the understanding of the pathogenesis of the disease, investigation of new therapies (e.g. selective estrogen receptor modulators (SERMs)) and evaluation of prosthetic devices in osteoporotic bone. Animal models that have been used in the past include non-human primates, dogs, cats, rodents, rabbits, guinea pigs and minipigs, all of which have advantages and disadvantages. Sheep are a promising model for various reasons: they are docile, easy to handle and house, relatively inexpensive, available in large numbers, spontaneously ovulate, and the sheep's bones are large enough to evaluate orthopaedic implants. Most animal models have used females and osteoporosis in the male has been largely ignored. Recently, interest in development of appropriate prosthetic devices which would stimulate osseointegration into osteoporotic, appendicular, axial and mandibular bone has intensified. Augmentation of osteopenic lumbar vertebrae with bioactive ceramics (vertebroplasty) is another area that will require testing in the appropriate animal model. Using experimental animal models for the study of these different facets of osteoporosis minimizes some of the difficulties associated with studying the disease in humans, namely time and behavioral variability among test subjects. New experimental drug therapies and orthopaedic implants can potentially be tested on large numbers of animals subjected to a level of experimental control impossible in human clinical research.

The purpose of this study was to compare the effects of inhaled isoflurane and a constant infusion of propofol on maternal haemodynamics and uterine arterial and umbilical venous flows in pregnant ewes. Late term pregnant ewes (n = 5) were randomly assigned to receive either inhaled isoflurane or an intravenous infusion of propofol for 1 h, each on separate occasions. Maternal systemic arterial, right atrial and pulmonary arterial blood pressures, cardiac index, systemic vascular resistance index, stroke volume index, heart rate, and uterine arterial and umbilical venous flows were determined over the 1 h period of each treatment. Data were analysed using an univariate analysis of variance for repeated measures performed on the ranks of the data. Propofol anaesthetized ewes had significantly higher heart rate (P = 0.0040), mean arterial pressure (P = 0.0003) and cardiac index (P = 0.0475) compared to isoflurane anaesthetized ewes. There were no significant differences in uterine arterial flows, umbilical venous flows, or other measured variables. Continuous propofol infusions maintain maternal haemodynamics at significantly higher levels than does inhaled isoflurane, while uterine arterial and umbilical venous flows do not differ significantly.

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