Vasomotor reversal of dale
- 1. vasomotor reversal of dale may be looking difficult, right? Let us understand it in very easy way. We should remember following points about receptors: 1. Adrenaline acts on - α1, α2,β1,β2,β3 2. α1, - presents in blood vessels – causes vasoconstrictions- increases blood pressure 3. β2 – presents in blood vessels- causes vasodilatation – decrease in blood pressure We should also keep in mind that 1. At lower concentration of adrenaline β2 – receptors are more sensitive 2. At higher concentration adrenaline acts on all receptors Now to observe effects on blood pressure of adrenaline we have to give adrenaline intravenous rapidly. (In dog) 1. When we give adrenaline intravenously, initially the concentration of adrenaline is high. a. So it will act on α1, β2. b. But actions of α1 (vasoconstriction), will predominate over actions of β2 (vasodilatation) c. So there will be rise in blood pressure 2. Within few second level of adrenaline will decrease due to its rapid metabolism and neuronal re- uptake a. At lower concentration only action of β2 will predominate b. So only fall in Blood pressure seen 3. So at this level you can observe initially rise in blood pressure and then after fall in blood pressure. This is called biphasicresponse (It is not vasomotor reversal of dale)
- 2. So what is vasomotor reversal of dale? After biphasic response if we administer non-selective alpha blocker It blocks the alpha receptors, hence α1 mediated vasoconstriction Now, if you give Adrenaline again what will happen? Only β2 mediated action occur (why?- because α1 receptors are blocked by alpha blocker) So only fall in blood presser is seen, rather than biphasic response This phenomenon is called Vasomotor reversal of Dale
- 3. To understand Re-reversal of vasomotor reversal, We need to understand Vasomotor reversal of dale. Please read Vasomotor reversal of dale on below mention link. http://pharmacologymbbs.blogspot.in/2015/08/vasomotor-reversal-of-dale.html So As We have seen in Vasomotor reversal- 1. First give adrenaline and observe biphasic response 2. second We give non-selective alpha blocker 3. At last We give adrenaline again and observe only fall in BP due to unopposed β2 mediated action This was all about vasomotor reversal of dale. Now what about Re-reversal? - ( As name suggests re- reversal, We have to reverse the action which happened in Vasomotor reversal of Dale) For this 1. First We give adrenaline intravenously and observe biphasic response 2. Now, second step, We give non Selective Beta Blocker (instead of non selective alpha blocker) It blocks the β2 receptors, hence β2 mediated vasodialatation will be blocked 3. Now, if you give Adrenaline again what will happen? Only α1 mediated action occur- vasoconstriction - rise in blood pressure (why? because β2receptors are blocked by beta blocker) So only rise in blood presser is seen, rather than biphasic response This phenomenon is called Re-reversal of Vasomotor reversal of Dale