[Physiology and physiopathology of substance P]

The neuropeptide substance P is considered a transmitter candidate of central and peripheral neurons, particularly of small diameter sensory afferents. Electrical stimulation of these fibers leads to release of substance P from the spinal cord. Since substance P injected intrathecally causes pain behaviour and since substance antagonists inhibit reactions to nociceptive stimuli, substance P is a likely transmitter of a population of nociceptive C-fibers. Release of substance P from the peripheral endings of these fibers leads to neurogenic inflammation, i.e. vasodilatation and protein extravasation. In the skin and eye substance P is involved in inflammatory reactions following thermal and chemical injuries. Similarly, stimulation of substance P fibers of the respiratory tract by various irritants causes mucosal edema and, at least in the guinea pig, also bronchoconstriction. Substance P antagonists inhibit neurogenic inflammation in animal experiments and may, applied topically, gain therapeutic value.