Pharmacology for Dentistry

134 Section 3/ Drugs Acting on ANS

Uterus: The response of the uterus to the
catecholamines varies according to species
and absence or presence of pregnancy. In
rats both pregnant and nonpregnant uterus,
relaxation is produced while in rabbits both
pregnant and nonpregnant uterus is
contracted. In human beings, nonpregnant
uterus is contracted while pregnant uterus
is relaxed in the last month of pregnancy.

Eye: Mydriasis occur due to contraction
of radial muscles of iris, intraocular tension
is lowered due to less production of the
aqueous humor secondary to vasoconstric-
tion and conjunctival ischemia due to con-
striction of conjunctival blood vessels.

Action on other smooth muscles & other
miscellaneous actions:

a. Urinary bladder: Detrusor is relaxed

(b) and trigone is constricted (a) and

both the actions tend to inhibit

micturition.

b. Spleen: In animals, it causes

contraction (due to its a action) of the

splenic capsule resulting in increase in

number of RBCs in circulation.

c. It also cause contraction of retractor

penis, seminal vesicles and vas

deferens.

d. Adrenaline causes lacrimation and

salivary glands are stimulated.

e. Adrenaline increases the blood sugar

level by enhancing hepatic glyco-

genolysis and also by decreasing the

uptake of glucose by peripheral tissues.

Adrenaline inhibits insulin release by

its a-receptor stimulant action whereas

it stimulates glycogenolysis by its b

receptor stimulant action.

f. Adrenaline produces leucocytosis and

eosinopenia and accelerates blood

coagulation and also stimulates platelet

aggregation.

Action on CNS: Catecholamines do not

produce any marked CNS effects because

they do not cross blood brain barrier

satisfactorily. However, adrenaline may

produce restlessness, apprehension,

excitement and tremors on intravenous or

intracarotid injection.

Pharmacokinetics

Catecholamines are absorbed from the

intestines, but are rapidly degraded in gut

and liver by enzymes MAO and COMT.

Thus they are inactive on oral

administration.

Adverse Effects

Restlessness, anxiety, tremor, head-

ache. Both adrenaline and noradrenaline

cause sudden increase in blood pressure,

precipitating sub-arachnoid haemorrhage

and occasionally hemiplegia, and ven-

tricular arrhythmias. May produce angi-

nal pain in patients with ischemic heart

disease.

Contraindications

a. In patients with hyperthyroidism.

b. Hypertension.

c. During anaesthesia with halothane and

cyclopropane.

d. In angina pectoris.

Therapeutic Uses

Allergic reaction: Adrenaline is drug of

choice in the treatment of various acute al-

lergic disorders by acting as a physiological