Preconstriction

After washing, endothelium-denuded rings were used to determine the vasoconstrictive response to norepinephrine (NE, 10 −11 –10 −4 moles/liter) and to evaluate the endothelium-independent relaxation to the NO donor sodium nitroprussiate (SNP, 10 −11 –10 −4 moles/liter) after preconstriction with PE 10 −6 moles/liter.