Biomedical subjects
Publications and source records attributed to J Atkinson.
Rats with permanently implanted right jugular vein cannulae were either pre-treated with increasing doses of caffeine for up to 98 h, or underwent no pre-treatment. Both groups were then presented with a lever, the pressing of which caused a self-injection of a caffeine solution. For both groups, some of the rats self-administered caffeine for up to 4 days and then their activity stopped; the other rats did not self-administered caffeine.
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An automatic device for the isolated rabbit heart is described. Test solutions are perfused from reservoirs via valves, the sequence and time of opening of which is controlled by a programmable unit. The perfusate was pushed through the heart at a constant flow-rate, with pressure measurement serving as an indicator of preparation stability. The system worked well giving reproducible results without tedious, repetitive manual work. The results obtained with caffeine were in line with those reported in the literature, there being a dose-dependent increase in rate and force of contraction.
The effect of caffeine and coffee on the sleeping time induced by barbital was tested in rats. It was found that caffeine pretreatment shortened barbital-induced sleeping time and that coffee had an effect in direct proportion to its caffeine content; decaffeinated coffee was without effect. It was hypothesized that the shortening was due to an interaction at the brain level. This hypothesis was tested using hexobarbital which is metabolized by the liver whereas barbital is only negligibly so metabolized. Pretreatment with caffeine was found to shorten the hexobarbital sleeping time even though the brain concentration of the latter was actually elevated. It was also shown that caffeine pretreatment was much less effective than phenobarbital pretreatment in stimulating the enzyme systems in the liver which metabolize hexobarbital, aminopyrine and ethylmorphine (in vitro). Consequently, it is concluded that caffeine stimulation of liver metabolism is a relatively minor factor in the shortening of barbiturate sleeping time by caffeine in comparison to the brain interaction of these two drugs.
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1. Investigations were carried out on the antagonism of the action of carbamylcholine chloride on the isolated fundus of the rat stomach by several tricyclic antidepressants.2. The anticholinergic potency of the compounds was in the order: GP 45437>amitriptyline>protriptyline>desmethylimipramine>opipramol. All of the antagonists were less effective than atropine.3. Statistical analysis was carried out to determine whether the theory of competitive antagonism would fit the data obtained.
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