Simplicified version

4. (Adrenonegative drugs)

1. Sympatholytics

List of drugs

Reserpine

Guanethidine

Mechanism of action

These drugs produce inhibition of releasing of norepinephrine from presynaps, As result, there will be the decreasing of norepinephrine concentration in the synaptic cleft and absence of stimulation of α₁, α₂, β₁, β₂- adrenoreceptors.

Pharmacological effects

Previous time you studied the pharmacological effects of Indirect adrenomimetics (see my previous material). For today topic «Sympatholytics» pharmacological effects will be strongly opposite (see table):

Type of receptors	Organ	Effect
Absence of stimulation of α1- adrenoreceptors	Blood vessels	Dilation (due to relaxation of smooth muscles of blood vessels)
Absence of stimulation of α2- adrenoreceptors	Blood vessels	Dilation (due to relaxation of smooth muscles of blood vessels)
Absence of stimulation of β1- adrenoreceptors	Heart	Decreasing of heart rate, heart contractility, heart conductance and heart excitability
Absence of stimulation of β2- adrenoreceptors	Bronchi	Constriction (due to contraction of smooth muscles of bronchi)

Indications

1. Hypertension (chronic treatment)

Reserpine, Guanethidine → absence of stimulation of α₁, α₂-adrenoreceptors → dilation of blood vessels + absence of stimulation of β₁-adrenoreceptors → decreasing of heart rate and heart contractility = due to dilation of blood vessels and decreasing of heart rate and heart contractility there will be the decreasing of arterial pressure.

2. Tachyarrhythmia (tachycardia)

Reserpine, Guanethidine → absence of stimulation of β₁-adrenoreceptors → decreasing of heart rate → inhibition of tachyarrhythmia (tachycardia).

2. Alfa-adrenoblockers

List of drugs

α₁, α₂-adrenoblockers: phentolamine mesylate

α₁- adrenoblockers: prazosin hydrochloride

Mechanism of action

Phentolamine produces direct blockage of α₁, α₂-adrenoreceptors.

Prazosin produces direct blockage of α₁-adrenoreceptors

Pharmacological effects:

Previous time you studied the pharmacological effects of Alfa-adrenomimetics (see my previous material). For today topic «Alfa-adrenoblockers» pharmacological effects will be strongly opposite (see table):

for phentolamine:

Type of receptors	Organ	Effect
Blockage of α1- adrenoreceptors	Blood vessels	Dilation (due to relaxation of smooth muscles of blood vessels)
Blockage of α2- adrenoreceptors	Blood vessels	Dilation (due to relaxation of smooth muscles of blood vessels)

for prazosin:

Type of receptors	Organ	Effect
Blockage of α1- adrenoreceptors	Blood vessels	Dilation (due to relaxation of smooth muscles of blood vessels)

Indications

1. Relieving of hypertensive crises

Phentolamine → blockage of α₁, α₂-adrenoreceptors → dilation of blood vessels → decreasing of arterial pressure.

2. Hypertension (chronic treatment)

Prazosin → blockage of α₁-adrenoreceptors → dilation of blood vessels → decreasing of arterial pressure.