Physiology of tachykinins:
The tachykinins are a group of plasma kinins that play a major role in
inflammation and neurotransmission hence most of them are referred to as
neuropeptides.13,14,15,16 The two human tachykinin
genes are
called TAC1 and TAC3.17
The major source of tachykinins is in the gut are enteric neurons,
followed by nerve fibres from dorsal root and vagal ganglia.
Tachykinin-containing fibres surround enteric ganglia, ramify through
muscle, form a perivascular mesh around submucosal arteries, and supply
the mucosa. This explains the fact of isolation of substance P from
Gut.2 The important roles of tachykinins include
Neuro-neuronal transmission, Protective secretory responses to
infection.18,19,20,21,22 Tachykinins also participate
in the inflammatory responses to infection, including formation of
granulomas, sites of chronic inflammation that prevent spread of
infectious agents.23 Tachykinins stimulate smooth
muscle contraction of the human ureter, mostly by activating the
NK2R.24 Tac1 , Tac3 ,
and Tac4 are expressed by human sperm, and tachykinins increase
sperm motility by NK1R- and
NK2R-dependent mechanisms.25 Mouse and
human keratinocytes express NK1R and
NK2R. The consensus of multiple studies is that SP and
NKA control the capacity of keratinocytes to serve as cytokine factories
by regulating production of proinflammatory
cytokines.26 Thus tachykinins are involved in a vast
array of physiological functions that makes them a potential target for
drug development.