Which procedure or drug would induce the changes of the blood pressure and heart rate observed 3 min after the beginning of the experiment?
a. Vagus nerve stimulation
b. Acetylcholine administration
c. Histamine administration
d. Two of the above
e. None of the above
A: vagus nerve stimulation
A is correct
Stimulation of the distal vagus would decrease both the heart rate, due to direct parasympathetic inhibition of the sinus node, and the blood pressure, due to decreased cardiac output.
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D is wrong b/c All of the drugs listed, as well as vagus nerve stimulation, would induce a decrease in blood pressure. However, only one of these conditions would produce a decrease of the heart rate also.
C is wrong b/c Histamine administration would decrease the blood pressure not the heart rate. The heart rate after histamine is usually slightly elevated because decrease of the blood pressure induces sympathetic activation through baroreceptors.
@ maryam,
The question says CHANGES not decrease in BP and HR !!!
@soprax i believe it might of been a typo but i agree.. but either ways u said the answer might be C.... how does histamine effect the heart besides reflex?.... so wouldn't it still be D... ACh and vagus???
Soprax - Question says Changes and not decrease in BP AND HR, True. So histamine causes decrease in BP and in reflex it cause little elevation in HR BUT.. key words are "Changes in both BP and HR" and "within 3 mins". Along with maryam's explanation, histamine will take more than 3 mins to show its reflex action. I hope it makes sense.
Zen - Ach will not show its action b/c it will be degraded by achetylcholine esterase ( REMEMBER one of the way how ach is taken away after its action is done; how it difusses away from the synapse / NMJ and degraded by ach esterase) Thats why Ach is not use widely as a treatment option for e.g in myasthenia gravis.
I hope it makes sense.
valid point.... will note
thank you @wimobile great reasoning!!
Q is asking about the Changes of both BP and HR 3 minutes after the begining of drug administeration(at the same time)....we should look for a drug that has effect on both HR and BP simultaneously...stimulation of Vagus nerve causing change on both HR and BP at the same time due to direct parasympathetic inhibition of the sinus node, and the blood pressure, due to decreased cardiac output.
But in the other choices the drug causing a change on one factor directly and indirect manner on the other one subsequently.
for example choice B..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 ,and Histamine administration would decrease the blood pressure not the heart rate. The heart rate after histamine is usually slightly elevated because decrease of the blood pressure induces sympathetic activation through baroreceptors.