ABSTRACT
Peripheral vascular resistance is important to maintain arterial blood pressure and a normal blood circulation. Smooth muscle cells in the peripheral resistance arteries and arterioles contract partially under physiological conditions and play a key role in producing the basal tone of these blood vessels. The mechanisms underlying this basal tone are still not fully understood. As most of the blood vessels are innervated by the autonomic nerves, neural activity may be involved. The endothelium may also be playing a role in the production of the basal tone, because the endothelial cells release not only relaxing factors but also constricting substances such as endothelin (Yanagisawa et al., 1988).
