Japanese journal of pharmacology
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A new theory is presented to describe the effect of functional antagonism on the competitive antagonism between adrenergic beta-mimetics and beta-blockers. According to this theory the shape of the log (dose ratio-1) vs.--log [B] curve and the apparent pA2 value in competitive antagonism should be affected by functional antagonism when the agonist is taken up by the saturable uptake process, and this was experimentally confirmed. ⋯ The log (dose ratio-1) vs. --log [B] curve is ISO-Prop competitive antagonism was shifted variously depending on the concentration of a spasmogen used. Theoretical predictions and experimental results were in good parallel.
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The cardiovascular effects resulting from intracisternal (i.c.) injections of sympathomimetic amines were studied in alpha-chloralose-urethanized rats. Norepinephrine (0.5-5 mug i.c.) caused a typical rise in blood pressure with no significant change in heart rate and a fall in blood pressure with a bradycardia, which were completely blocked after treatment with phentolamine (10-50 mug i.c.) L-isoproterenol (0.05-0.5 mug i.c.) and trimetoquinol (0.5-3 mug i.c.), a beta-sympathomimetic agent, usually caused a fall in blood pressure with a tachycardia, which was reduced after treatment with propranolol (10-50 mug i.c.), but trimetoquinol was inclined to cause a rise in blood pressure with a tachycardia. ⋯ Tyramine (0.5-1 mg i.c.) caused mixed blood pressure responses presumably due to a release of norepinephrine and epinephrine, and these responses were partially blocked after treatment with phentolamine (100 mug i.c.) or propranolol (50 mug i.c.). These observations suggest that both alpha- and beta-sensitive adrenergic zones may exist on the vasomotor center of the pons and medulla in rats, and both norepinephrine and epinephrine might centrally play a physiological role as the neurotransmitters controlling blood pressure in rats.
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Curves of experimentally plotted log (dose ratio-1) vs.-log [B] for the antagonism between adrenergic beta-mimetics, isoproterenol (ISO) and trimetoquinol (TMQ), and various beta-antagonists in relaxation of guinea-pig trachea could not be reasonably fitted to Schild's equation which has been commonly used in the analysis of drug-antagonism. Taking into consideration the saturable uptake process of the drug used herein, the equation presented in this paper fitted fairly well to the experimental curves and explains the following results: 1, TMQ was more strongly antagonized than ISO by all the blocking agents tested, that is, the apparent modes of antagonism were different between ISO and TMQ although they are considered to interact with the same receptor site. 2, The slope of the curve for a given antagonist markedly differed between ISO and TMQ. ⋯ This was experimentally confirmed: i.e., ISO was potentiated about 8 fold by inhibiting the uptake process with dibenamine while TMQ was not. By pretreatment with dibenamine, the log (dose ratio-1) vs.-log [B] curve for the ISO-propranolol antagonism was shifted upward and superimposed with the theoretical curve of antagonism in which uptake of the agonist was neglected.
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The cysteamine-induced duodenal ulcer reported by Selye et al. was investigated and the optimum conditions for the production of ulcers in rats were established. A single subcutaneous administration of cysteamine between 200 and 500 mg/kg produced ulceration in a dose-dependent manner in the duodenum within 18 hr. Female and older rats were more susceptible to cysteamine than male and younger ones, respectively. ⋯ Tegragastrin or bethanechol increased the severity of cysteamine-induced ulceration. These data suggest that gastric juice may play an important role in the pathogenesis of cysteamine-induced ulcers. The present study provided an excellent animal model for studying the mechanism of duodenal ulcers and screening of antiulcer agents.