Relation of substance P to stress and catecholamine metabolism.

Most research on substance P deals with its presumed function in the nervous system. Both excitatory and inhibitory actions have been observed in pharmacological studies. For example, substance P has a dual action on nociception in mice: it produces analgesia or hyperalgesia, depending on the dose and on the individual sensitivity to pain. This is interpreted to mean that substance P is capable of normalizing responsiveness to pain. Thus substance P could be classified as a regulatory peptide, or 'regulide'. A similar normalizing action of substance P was found in stress-induced disorders of sleep, behaviour and blood pressure in rats. The mechanism of this normalizing action is not yet clear. The decrease in activity observed for dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase in adrenal glands of rats treated with the peptide may serve as a preliminary hypothesis.