Determination of pA2
Antagonism parameter (pAx): for competitive antagonism, when the agonist and antagonist combined, X times the concentration of agonist effect produced exactly equal to the effect produced by the agonist without the addition of the antagonist, the negative logarithm of the molar concentration of the antagonist added to the pAx, often 2 times the concentration of the agonist experiments, i.e., pA2, used to illustrate the strength of the action of the antagonist and the nature of the receptor, which is one of the commonly used measurement parameters of the experimental teaching of pharmacology, which is important for pharmacological significance. It is one of the commonly used parameters in pharmacology teaching and has important pharmacological significance.
Operation method
antagonistic method
Principle
In pharmacology experiments, there are many factors affecting the experimental results, some of which can be controlled, and some of which are difficult to control. In order to reduce the influence of multi-factors and difficult-to-control factors, a control group should be set up at the same time in the experiments, and comparisons between the control group and the experimental group should be made to eliminate the influence of various extraneous factors, so that the experimental results can be minimized as much as possible, and to achieve the purpose of correctly evaluating the effect of the drug.
Materials and Instruments
Rabbit Move I. Experimental set-up and its connections: Caveat 1. do not pull the vascular specimen with force;2. Care for the sensor and operate it gently;3. Dosing should be timely and accurate. For more product details, please visit Aladdin Scientific website.
Nutrient solution Alpha-blocker phentolamine
Thin rod Wire Bath Tension sensor
II. specimen production:
Rabbits weighing about 2 kg, male or female, were stunned and the thoracic aorta was cut open and immediately placed in Kerb's solution with a mixture of 95% O2 and 5% CO2 gas. The perivascular connective tissue was carefully removed, attached to a thin rod, cut into a 25×3 cm spiral strip, and ligated at each end with a length of thread. The specimen was placed in a bath containing 10 ml of Kreb's solution (pH 7.3 to 7.4, 1 to 2 bubbles/second of gas mixture passed at 37 °C). One end was fixed to a small hook on the specimen plate and the other end was connected to a tension sensor. The load was 4 g and equilibrated for 1 h, during which time the nutrient solution was changed every 15 min.
Administration: norepinephrine (NA) was added to the bath in the following order. 
NOTE: Give the next dose if there is no response after the previous dose or if there is a contraction to maximum effect. When the contractile response no longer increases after administration of the next dose, the specimen is rinsed until it returns to baseline and the alpha-blocker phentolamine (phentolamine, Regintin) is added at 10-5 mol/L 0.03 ml, i.e., a bath concentration of 3 × 10-8 mol/l, and the above dosing steps are repeated after 15 min.
The volume effect curve was plotted:
The percentage response of each dose of NA before and after phentolamine administration was calculated separately using the maximum response of the control curve as 100%. The negative logarithm of the gram concentration of phentolamine was used as the abscissa, and the percent response was used as the abscissa to plot the potency curves on coordinate paper.
The pA2 value was calculated:
According to the formula: pA2 = PAx + log(Ab/A-1)
Where: Pax: negative logarithm of competitive antagonist gram concentration.
Ab: dose of agonist causing 50% response in the presence of competitive antagonist (ED50')
A: dose of agonist required to elicit 50% response in the absence of antagonist (ED50)
The pA2 value was obtained by substituting each of the obtained data into the formula.