Inhibition of prostaglandin synthesis does not affect contractile responses to noradrenaline, serotonin, angiotensin II nor endothelin-1 in human forearm isolated veins.

1. The functional role of endogenous cyclo-oxygenase products was examined in the human forearm isolated vein. 2. Six healthy normal adult males (age > 18 years old) were recruited. Forearm veins were biopsied and ring segments mounted in standard organ baths for recording of isometric force. 3. Noradrenaline (-log molar EC50: 7.75 +/- 0.19; -log molar threshold concentration: 8.80 +/- 0.20), 5-hydroxytryptamine (-log molar EC50: 7.52 +/- 0.17; -log molar threshold concentration: 9.50 +/- 0.64), angiotensin II (-log molar threshold concentration: 9.00 +/- 0.28) and endothelin-1 (-log molar threshold concentration: 9.13 +/- 0.47) were equipotent in this preparation. Indomethacin (10 microM) had no effect on either the threshold concentration or EC50 of noradrenaline, 5-hydroxytryptamine nor the threshold concentration of angiotensin II nor endothelin-1. 4. Sodium nitroprusside (1 nM-10 microM) relaxed noradrenaline-precontracted preparations. Evidence of minimal endothelial influence was confirmed by the lack of relaxant response to acetylcholine (1 nM-10 microM). Histology using silver staining confirmed that endothelial cells were absent over greater than 90% of the lumen surface. 5. We conclude that endogenous prostanoids derived from smooth muscle cells, either released basally or agonist-stimulated, do not play a role in the regulation of vascular tone in the human forearm isolated vein.