Question

Sir Henry Dale was noticed that adrenalin decreases blood pressure if another unknown agent is administered to the organism before the administration of adrenalin. The same dose of adrenalin increases blood pressure sharply if there is no preadministration of this unknown agent and when the unknown agent is admistered alone, no significant change in blood pressure is observed. Discuss this experiement based on your knowledge about physiological activity of adrenalin, adrenergic receptors and pharmacodynamic drug interaction principles. What kind of an action could this unknown agent exert, which type of receptors migh it be acting on and how may it affect its receptors (agonist, antagonist, inverse agonist etc.)?

Answer 1

The adrenaline works by acting on the beta 1 receptors, which leads to the increase in the heart rate, breathing rate etc producing the fighht or flight response. The drug used prior to injecting adrenaline in the question must block these receptors so that the adrenaline can longer bind to these receptors. This unknown drug produces the opposite effect to adrenaline when bound to the same receptor (beta 1 receptor). Hence, it acts as a inverse agonist to adrenaline.