00:01
Hi, welcome to pharmacology by Lecturio. We are going to
continue our journey talking about the autonomic nervous system
and the drugs that we use to control it. My name is Dr.Pravin
Shukle. We are going to talk today about some of the drugs
that are mimicking the sympathetic nervous system. Let's take
a look at sympathomimetics. We have direct activators and
indirect activators that imitate the effects of excess adrenaline
on the human body. Let's first talk about alpha agonist.
00:35
Now the classical drug of alpha agonist category is norepinephrine.
It is a non selective agent. Alpha 1 selective agent is
phenylephrine and an alpha 2 selective agent is clonidine. It
is important that you memorise these drugs. They are going to be
on your exam and they are going to be prototypical drugs. We
won't talk about other alpha 1 and alpha 2 selective drugs,
we will just focus on these ones. What about beta agonist. The
classical or prototypical beta agonist is epinephrine which is
endogeneously produced amine. The nonselective agents are
epinephrine and isoproterenol. The beta 1 selective agonist
is dobutamine. And the beta 2 selective agonist is albuterol
and salbutamol. Salbutamol is more commonly known as ventolin.
01:29
And these are inhaled drugs. Remember that beta 2 means you
have two lungs. These are drugs that are active in the lungs,
they are generally inhaled medications. In terms of the indirect
activators, there is release of adrenaline from the terminal
nerve button and that's caused by amphetamines. And there are
reuptake inhibitors, drugs like cocaine and tricyclic antidepressants
work through that mechanism. The indirect activators also
include dopamine. Now dopamine at low dose activates dopamine
receptors. At intermediate dose, activates beta receptors, and
at very high doses, activates alpha receptors. I'm going to
tell you a little story about dopamine so that you remember. If
you remember I gave you a picture of the terminal nerve button
of both the cholinergic and the adrenergic nerve. Let's take a
look in more detail at the production of norepinephrine in the
adrenergic terminal nerve button. We start with tyrosine.
Tyrosine is converted by a hydrolase into dopa
and dopa is converted into dopamine. Now dopamine also undergoes
a chemical reaction and during that chemical reaction it is also
packaged into vesicles. The chemical reaction converts it into
norepinephrine and that norepinephrine is stored in this
vesicles or bags of enzymes. The norepinephrine vesicle is
kept at the end of the terminal nerve button until it's needed.
03:02
And when there is a signal from the nerve, that signal is
usually calcium, the norepinephrine is released into the
synaptic cleft. Now you need calcium in order for that synaptic
cleft, sorry for the vesicle to bind with the membrane
and release into the synaptic cleft. Okay, so now your
norepinephrine is in the synaptic cleft. There is 1 of 3
things to norepinephrine now. It will either be diffused away,
or metabolized and therefore made inactive or it will activate
the adrenoreceptor itself and cause an effect. Or it will get
reuptaken. So reuptake is usually mediated through the
norepinephrine transport molecule and you can see it there it
just appeared. Now, we do have inhibitors of that NET molecule.
03:56
That's tricyclic antidepressants and cocaine. So cocaine
inhibits the transport molecule leaving more epinephrine
in the synaptic cleft and that's how you get the hyperadrenergic
response with cocaine. Now incidentaly in the brain
tricyclic antidepressant do have this effect as well and
that's why you have a reduction in depression in some cases.