1. The effects of extracellular Na+ removal on agonist-induced contrac
tion of vascular smooth muscle in vitro are reviewed. 2. The effects o
f extracellular Na+ removal on contraction vary depending upon the ago
nist and vessel. 3. Factors that may influence the effects of extracel
lular Na+ removal on agonist-induced contraction include the compound
substituted for Na+, time of tissue exposure to lowered extracellular
Na+, concentration of extracellular Na+, agonist concentration, presen
ce of the vascular endothelium and presence of basal tone. 4. The pote
ntial influence of these factors needs to be determined and minimized,
in studies that investigate the role of extracellular Na+ in agonist-
induced contraction.