The mechanical functioning of the stomach has been well researched (1). The contractions that mix, break up, and propel the gastric bolus in the main body and antrum have been described in detail and have been partially modeled mathematically. Because the antral forces are particularly important in the mixing and break up of food, they have been measured using manometers, pressure transducers, MRI imaging of agar beads of differing strength (2), and other methods (3, 4). The chemical and biochemical environment of the stomach, its acid and digestive enzymes, and their production and activity rates under different conditions have been studied for many years, and reference ranges established mainly for diagnostic purposes. All these areas have been extensively reviewed (5-7).Despite this understanding of gastric function, many in vitro digestion studies use grossly simplified systems that often include food homogenization, nonphysiological mixing and shear, and unrealistic acid and enzyme concentrations that do not change over time as happens in vivo.This paper describes the design and operation of a computer-controlled dynamic gastric model (DGM) that was built to investigate the effects of the biochemical and physical processing of foods and oral pharmaceuticals.Our intention was to draw together the physical and biochemical features of the human stomach with data on gastric residence time and emptying profiles and to design a computer-controlled mechanical stimulation that works in real time with realistic chewed foods or meals and oral pharmaceutical and nutraceutical products.

It has been proposed that the adult castrated male rat may be used as a model of human postmenopausal osteoporosis. If such a model is valid then the total body calcium of castrated rats should progressively decrease compared with normal rats. To search for this age-related difference, it will be necessary to use a measurement technique with a precision which is small compared with the magnitude of the change to be detected. From measurements of total body calcium by neutron activation and by whole body ashing of eight dead rats, it has been shown that total body calcium can be measured with an accuracy and precision which should allow distinction between the expected lifetime changes in normal and castrated rats.

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