Experimental competitive antagonism of histamine by diphenhydramine

Summary

This experiment is from the official website of the Fourth Military Medical University

Operation method

Experimental competitive antagonism of histamine by diphenhydramine

Principle

Histamine (histamine) can act locally on H1 receptors, causing contraction of gastric, intestinal, tracheal, and bronchial smooth muscle.The H1 receptor blocking drug diphenhydramine has a competitive antagonistic effect on histamine, and the strength of its effect can be reflected by the antagonism parameter (PA2 value). When an agonist is combined with an antagonist, the antagonist causes twice the concentration of the agonist to produce only the level of response of the original concentration of the agonist, and the negative logarithm of the molar concentration of the antagonist is the PA2 value. This experiment describes how to evaluate the strength of action of antagonists by determining the PA2 value of the antagonism parameter of benzylamine against histamine.

Materials and Instruments

Histamine phosphate solution Diphenhydramine solution Tai's solution BL-420 Microcomputer-based Biological Function Experiment System Constant temperature water bath box Mai's bath Tension transducer Surgical instruments Iron shelf table Petri dish Syringe

Move

1. Preparation of intestinal segments Take a guinea pig, execute it by striking the head, quickly dissect the abdomen, take out the ileum, and put it into a Petri dish containing table-top liquid. The ileum should be placed in a Petri dish with benchtop solution. Use a syringe to draw up the benchtop solution and rinse the intestinal tube at least three times to remove the intestinal contents. Cut the intestines into 2 cm long segments and set aside.

2. Contractile effect of histamine The intestinal segment was ligated at both ends, one end was fixed in the bath and the other end was fixed to the transducer. The bath was filled with 15 ml of bench-top solution, and the temperature was kept at 37±0.5°C. Oxygen was passed through the bath. After the intestinal segments were stabilized for 10 min, a baseline was recorded. Then different concentrations of histamine solutions were added (Table 23-1). After each addition, wait until the intestinal tube tension no longer increases before adding the next histamine solution. The contraction curve is recorded.

3. Antagonistic effect of benzydamine Rinse the bath with tabletop solution three times, the solution in the bath is still 15 ml, add 10-5 mol/L benzydamine 0.2 ml, wait until the intestinal tube is stabilized for 5 min, and then add different concentrations of histamine solution according to the above method, and record the contraction curve. Rinse the bath again, add 5×10-5 mol/L benadryl 0.2 ml, wait until the intestinal tube was stabilized for 5 min, add different concentrations of histamine solution according to the above method, and record the contraction curve. Similar to the above, after rinsing the bath, 10-4 mol/L benzylamine 0.2 ml was added and the contraction curve was recorded.

4. Calculation of PA2 value can be calculated using BL-420 microcomputer-based biofunctional experiment system, or using the three-point method and Scott ratio method (see bibliography for details).

(1) Measure the strength of the contraction response of each cumulative concentration of histiocytes, and then calculate the PA2 value using the efficacy as 100%.

(2) Find out the reaction percentage of each concentration, take the final concentration of histamine as the horizontal coordinate and the reaction percentage as the vertical coordinate to give the volume curve on the microcomputer or coordinate paper, and find out the approximate dose (ED50) required to cause 50% reaction of the agonist before and after the antagonist from the volume curve, and substitute into the formula to calculate the PA2 value.

PA2=log(E′/E-1)-logB

E′: ED50 of the agonist in the presence of antagonist;

E: ED50 of the agonist in the absence of antagonism;

B: molar concentration of the antagonist.

Caveat

1. When preparing the intestinal segments, pay attention to the operation specification and try to avoid damage, so as not to affect the subsequent determination of contractile function.

2. The amount of drug added must be accurate, and the drug can be added directly to the liquid level of the solution in the bath.

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