3. Introduction
• ANS is of vital importance for the well being of the
organisms
• ANS regulate the activities that are not under
voluntary control and that function below the level of
consciousness
• The efferent limb of ANS is anatomically divided into
sympathetic and parasympathetic system
4. • Many organs receive both sympathetic and
parasympathetic innervation and the two divisions are
functionally antagonistic in majority of cases
• Main function of sympathetic nervous system is
tackling stress and emergency whereas
parasympathetic part is associated with assimilation
of food and conservation of energy
5. History
• Elliot in 1905 suggested that sympathetic nerves
function by the release of adrenaline-like substance
• Dixon(1907) proposed vagus release a muscarine-like
substance
• Von Euler(1946) eventually showed sympathetic
transmitter was Noradrenaline
6. • Now, it is establishd NE is the principal transmitter of
most Sympathetic postganglionic fibres and of certain
tracts in CNS
• Epinephrine- adrenal medulla
• Dopamine-extrapyramidal system, mesocortical and
mesolimbic pathways
• Collectively these three amines are called as
Catecholamines
7. Adrenergic Receptors
• To understand diverse effects of the catecholamines and
related sympathomimetic agents, classification and
properties of different adrenergic receptors should be
known
• Ahlquist (1948) proposed designation α and β for
receptors on smooth muscle where catecholamines
produce excitatory and inhibitory responses respectively
• Exception is gut which is relaxed by activation of these
two receptors
8. • Rank order of potency of agonist
• α- receptor ---- Epi ≥ NE ˃ Isoprenaline
• β-receptor----- Isoprenaline ˃ Epi ˃ NE
9.
10. Receptor Regulation
• Responses that follow activation of all types of
adrenergic receptors result from G-protein mediated
effects
• β-receptor function by increasing production of
second messenger cAMP
11.
12.
13. • Exposure of catecholamine-sensitive cells and tissues
to adrenergic agonists causes a progressive decrease
in their capacity to respond to such agents
• Three process have considerable clinical significance
1. Desensitisation
2. Up and down regulation of receptors
29. REFERENCES
• Hager,A.(1981).Br.Med.Bull,37(3)287
• For various trial details (https://clinicaltrials.gov)
• HL sharma, KK sharma. Principles of Pharmacology. 2nd
ed.2011;p 901
• Katzung BG, Trevor AJ. Basics and clinical
pharmacology. 13th ed.McGraw Hill
education:2015;p664-5