Abstract
Knowledge of the significance of histamine in biological processes would be materially increased if assays of higher specificity and sensitivity were available. In the absence of such tests it is necessary to look for an increased number of reactions both chemical as well as biological, indicative of histamine. Such reactions might aid by their variety rather than by their specificity.
Experiments with various smooth muscle contractants, forms of shock, etc., now in progress in this laboratory made it advisable to compare the reactivity of chicken and mouse intestine to histamine and acetyl choline. This ratio is well known to be 2:1 in the guinea pig. 1 This figure agrees on the average with our own observations. However, we have not infrequently dealt with individual variations such as guinea pig intestinal strips with a histamine-acetyl choline ratio of 5 :1 or 1:1. It should be remembered that the iliac end of the guinea pig intestine is generally conceded to be more reactive than the duodenal.
The action of histamine and acetyl choline upon the mouse and chicken intestine does not appear to have been studied previously. The reactivity of the mouse uterus to histamine has been shown to vary with the concentration. 2 , 3 , 4 Low concentrations (1:1,170,000) stimulate contraction, while high ones (1:1,250) inhibit. Generally speaking, the use of intestinal strips in preference to other smooth muscle seems advantageous in some instances, because a number of strips of the same intestine can be used and checks can be run conveniently.
In the present determinations the Schultz-Dale technique was used. The bases were added to the isolated intestinal strip suspended in 25 cc. oxygenated Tyrode's kept at 38-40°C. Dilutions neutralized to phenolphthalein were made in Tyrode's solution so that 1 cc. contained a unit amount of histamine di-hydrochloride 20 or acetyl choline hydrobromide. 21 Absence of hydrolysis of the acetyl choline was insured.
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