Neuropeptide Y. A novel sympathetic stress hormone and more.

Several lines of evidence suggest that NPY is a neurotransmitter and neurohormone intricately involved in stress responses of the body, and as such should be considered a "stress molecule." Thus, circulating plasma NPY levels are increased by stress particularly if it is severe or prolonged. Stress stimulates the release of NPY from the sympathetic nerves and the adrenal medulla (in some species also from platelets), and in addition, modulates NPY inactivation. Stress-induced plasma NPY levels may reach the concentrations that are vasoconstrictive per se in addition to potentiating the actions of catecholamines. Reciprocally, elevated circulating levels of catecholamines during stress appear to induce hypersensitivity of blood vessels to NPY. Consequently, the peptide may be responsible for stress-induced regional vasoconstriction (splanchnic, coronary, and cerebral) but also may exert other actions that may be a part of the stress response: facilitate platelet aggregation, leukocyte adhesion, and macrophage activation. NPY release and actions appear to be up-regulated by testosterone and down-regulated by estrogens; therefore, NPY may be of particular importance to stress-induced cardiovascular events in men. In addition to acute vasoconstrictive effects, NPY exerts chronic actions and stimulates vascular smooth muscle proliferation and vascular hypertrophy, and hence, may be a link between stress and potential chronic changes in blood vessels.