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Reserpine

Source and chemistry

Natural alkaloid obtained from root of plant “rauwolfia serpentina” (snake root) which is abundant in the subcontinent (“chandan booti”)

Non polar, so can cross BBB rapidly. Central and peripheral action occurs (unlike guanethidine).

Mechanism of action
  1. Acting on Mg++- ATP pump, blocks it irreversibly (which is required for uptake of biogenic amines from cytoplasm into storage vesicles), thus depletion and decreased uptake of biogenic amines occurs in both central and peripheral neurons. As a result degradation of biogenic amines occurs.
  2. Serotonin decreased
  3. Conversion of dopamine into NE cannot take place, so synthesis of VMAT s required.

The drug crosses blood brain barrier.

Pharmacological actions
CVS

Decreases blood pressure. The fall is gradual as the drug blocks storage pumps both centrally and peripherally acting drug. Surprisingly no or mild postural hypotension is seen. This is because centrally acting drugs do not produce postural hypotension. Baroreceptor sensitivity is increased even further (some spare baroreceptors).

CNS

Decrease in dopamine produces antipsychotic effects

Decrease in NE produces antihypertensive effects

Decrease in serotonin produces antiemetic effects.

Therapeutic uses

1. Hypertension (0.25 mg/day very low dose)
2. Antipsychotic

Two entities affect CNS, depression on one hand and psychosis on other. Depression is because of decrease in biogenic amines while psychosis is always due to increase in number of biogenic amines (amphetamines). All drugs or conditions decreasing the levels produce depression. Reserpine depletes the stores of these biogenic amines, and was used in older days as antipsychotic.

3. Anti emetic

Adverse effects
CNS 
  1. sedation
  2. depression (producing suicidal tendencies, one reason why use discontinued)
  3. extra pyramidal effects decreasing the levels of biogenic amines in nigrostriatal pathway (due to decrease in dopamine, parkinsonism like symptoms)
  4.  nightmares
GIT

(block sympathetic system peripherally) 

  1. Diarrhoea
  2. Acidity (contraindicated in ulcers)
Nasal stuffiness

(due to increased blood flow)

Reproductive system

Decrease in libido

 Drug interactions

Interferes with action of drugs used in Parkinsonism like levo dopa.

Contraindications

Peptic ulcer

Depression

Guanethidine Resperpine
Source-Synthetic Natural
M.A.O- Reuptake 1 Blockage Mg++ ATP pump
Pharmacological Actions- tiphasic, biphasic, monophasic response  Gradual fall in blood pressure
Postural hypotension No or mild postural hypotension
Therapeutic Uses
Non-antipsychotic Anti-psychotic
No suicidal tendencies Suicidal tendencies

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