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What is Which of these statements depicts vasomotor reversal of Dale? and explain in detail?
Ans: C. Decrease in hea rate on adrenaline administration after phentolamine has been given (Ref: KDT 7/e e p131, 140).This was first demonstrated by Sir HH Dale (1913) and is called vasomotor reversal of Dale.Blockade of vasoconstrictor alpha-1 (also alpha-2) receptors reduces peripheral resistance and causes pooling of blood in capacitance vessels a venous return and cardiac output are reduced a Fall in BP.Postural reflex is interfered with a marked hypotension occurs on standing a dizziness and syncope. Hypovolemia accentuates the hypotension.Decrease in hea rate on adrenaline administration after phentolamine has been given depicts vasomotor reversal of Dale.The alpha-blocker abolishes the pressor action of adrenaline (injected IV in animals), which then produces only fall in BP due to beta-2 mediated vasodilatation.