B4.005 Autonomic Drugs

Question 1

why is the effect of Epi dose dependent?

Answer 1

greater effect at b2 than a1
decreased BP at low doses
increases BP at high doses

Question 2

why does Epi cause an initial increase in BP followed by a decrease?

Answer 2

direct a1 acts first to increase bc of high initial concentration
direct b2 is responsible for the fall over time due to the decreasing concentration of Epi

Question 3

discuss SNS control of HR

Answer 3

SNS innervation is via cervical and thoracic SNS ganglia
NE increases HR through b1
Epi contributes with strong SNS discharge

Question 4

discuss PNS control of HR

Answer 4

vagal innervation of SA node slows HR via ACh activation of muscarinic receptors

Question 5

what effect does Epi have on HR?

Answer 5

biphasic increases (tachycardia)
initially a direct b1 activation (Epi)
followed by reflex b1 activation by SNS as BP falls (NE)

Question 6

is there a PNS response to the administration of Epi?

Answer 6

yes
the initial spike in BP would stimulate a release of Ach at the heart
this is masked by direct effects of Epi, however

Question 7

how does NE affect BP?

Answer 7

just an increase due to a1 stim by NE

no b2 action by NE

Question 8

how does NE affect HR?

Answer 8

biphasic
initial increase by direct b1 activation by NE
followed by a decrease initiated by a PNS reflex mediated by muscarinic receptors

Question 9

how does isoproterenol affect BP?

Answer 9

decrease
direct b2 dilation
b1 increases SV and therefore increases pulse pressure

Question 10

how does isoproterenol affect HR?

Answer 10

direct pharmacologic effect by b1 stim
SNS reflex contributes as well due to decreasing BP
“double whammy”

Question 11

describe the phenomenon of epinephrine reversal

Answer 11

a1 and b2 actions of Epi oppose eachother simultaneously in smooth muscle
vascular tone at a given location is dependent on relative number of receptors
epinephrine reversal - a1 blockade makes the effects only beta mediated…so Epi looks like isoproterenol