Right. An irreversible competitive antagonist acts by decreasing the number of receptors available for binding an agonist. Therefore, even a high agonist concentration cannot overcome a irreversible blockade, and the maximal effect of an agonist is smaller in the presence than in the absence of an irreversible antagonist. There is, however, one other true statement in this item. Go back to Item III and try to find it.
No. An alpha1 selective antagonist like prazosin would not be expected to increase the blood pressure of an anesthetized cat. An initial effect of vascular alpha receptor blockade might be a decrease in blood pressure due to a decrease in total peripheral resistance. Go back to Item XV.
Right. Pretreatment with propranolol would block the stimulation of beta receptors by epinephrine. Therefore, only increased blood pressure, mediated by stimulation of alpha adrenergic receptors, and reflex bradycardia, would be observed after administration of epinephrine in a patient treated chronically with propranolol. There is, however, another drug or drug combination which would induce similar changes. Go back to Item XVI and try to find it.
Wrong. Isoproterenol and norepinephrine are both full agonists at cardiac receptors, so they should have similar maximal effects.
Wrong. You either skipped or forgot the answer to Item XII. Go back and answer Item XII before you try to answer Item XVII again.
Right. The dose of drug A which is required to produce effect Y is lower than an equipotent dose of drug C. Since potency varies inversely with the magnitude of the dose required to produce a given effect, drug A is more potent than drug C. There is, however, one other true statement in this item. Go back to Item I and try to find it.
Wrong. Acetylcholine administration would produce a decrease of the blood pressure but the heart rate would not decrease. Actually the heart rate after acetylcholine is usually slightly elevated because decrease of the blood pressure induces sympathetic activation through baroreceptors. Go back to Item XI.
Right. Atropine would increase the tachycardia induced by epinephrine because it prevents the reflex inhibition of the heart rate evoked by the increased blood pressure. There is, however, another drug which would also modify the epinephrine effect. Go back to Item XVI and think about it again.
Wrong. Pretreatment with phenoxybenzamine blocks the alpha adrenergic receptors. Therefore, phenylephrine cannot have a greater effect in a preparation pretreated with phenoxybenzamine than when it is given alone. Go back to Item IX.
Wrong. Physostigmine potentiates the effects of acetylcholine, which means that the same dose of acetylcholine will produce a greater effect in the presence of physostigmine. Curve D indicates smaller effects of the same doses than Curve C. Go back to Item IV.
Wrong. Pretreatment with d-tubocurarine blocks the effect of acetylcholine. Therefore, acetylcholine cannot have a greater effect in a preparation pretreated with d-tubocurarine, than when it is given alone. Go back to Item X.
Right. Occlusion of carotid arteries would decrease the blood pressure at the carotid sinus, and would produce an increased sympathetic outflow which would increase both heart rate and peripheral blood pressure. Go on to Item XIII.
Right. Cocaine potentiates norepinephrine by inhibiting the reuptake of norepinephrine into the sympathetic nerve endings. Since this uptake is the major mechanism for terminating norepinephrine effect, inhibition of the uptake shifts the dose-effect curve of norepinephrine to the left. Go to Item VII.
Wrong. Succinylcholine is a depolarizing blocking agent at the neuromuscular junction. You have to keep in mind that the effect of succinylcholine cannot be abolished by increasing the dose of acetylcholine. Go back to Item VIII.
Wrong. Propranolol would abolish the effect of carotid occlusion on the heart rate but not the effect of carotid occlusion or distal vagal verve stimulation on the blood pressure. Go back to Item XIII.
Wrong. Carotid occlusion produces an increase in the blood pressure and this increase would be antagonized by the alpha blocking agent phenoxybenzamine. Go back to Item XVIII.
Right. Phentolamine does not affect the increase of heart rate of an isolated heart because this effect is mediated through beta receptors and phentolamine is an alpha receptor blocking agent. Go to Item VIII.
Wrong. Prazosin is a pharmacological antagonist of norepinephrine, not of acetylcholine. Go back to Item II.
Right. Histamine would decrease blood pressure and induce secondary reflex tachycardia. There is, however, another treatment which would produce similar effects. Go back to Item XIX and try to find it.
Right. An average dose of epinephrine would increase both the heart rate, through simulation of beta adrenergic receptors, and the blood pressure, through stimulation of alpha adrenergic receptors. There is, however, one more drug or drug combination which would produce this effect. Go back to Item XIV and try to find it.
Right. A non-competitive antagonist reduces the maximal effect, but does not change the ED50. There is, however, one other true statement in this item. Go back to Item III and try to find it.
Correct. None of the drugs listed would markedly increase both the blood pressure and the heart rate. Go on to Item XVI.
Wrong. You forgot one other agent which would also modify and/or abolish the heart rate changes observed following the administration of a high dose of epinephrine. Read a comment corresponding to this agent before proceeding to Item XVII.
Wrong. Physiological antagonism is caused by agonist and antagonist acting at two independent sites and inducing independent, but opposite effects. Phentolamine and norepinephrine act at the same site (alpha-receptor). Go back to Item II.
Wrong. There is a curve which represents the effect of phenylephrine in a preparation pretreated with phenoxybenzamine. Go back to Item IX and try to find it.
Wrong. You forgot one other treatment which would also increase the blood pressure and decrease the heart rate. Read a comment corresponding to this agent before proceeding to Item XVII.
Right. Isoproterenol is more potent than norepinephrine at cardiac B1 receptors. Go to Item VI.
Wrong. Physostigmine modifies acetylcholine effects. Before you go back to Item IV, review the pharmacologic effects and mechanism of action of physostigmine.
Right. D-tubocurarine is a reversible competitive antagonist of acetylcholine at the neuromuscular junction. The blocking effect of d-tubocurarine can be overcome by anticholinesterase drugs, which increase the concentration of acetylcholine at the neuromuscular junction.
Wrong. There is one condition which would produce changes of the blood pressure and heart rate similar to those which occurred 3 minutes after the beginning of the experiment. Go back to Item XI and try to find it.
Wrong. The effect of norepinephrine in a preparation pretreated with phentolamine is represented by a different curve. Go back to Item VII.
Wrong. There is a curve representing the effect of acetylcholine in a preparation pretreated with physostigmine. Go back to Item IV and think about it again.
Wrong. There is only one drug or procedure which would simultaneously increase both blood pressure and heart rate. Go back to Item XII and try to find it.