. Amplification of sumatriptan-induced contraction in rabbit saphenous vein but not in basilar artery. Am J Physiol Heart Circ Physiol 284: H719-H726, 2003; 10.1152/ajpheart.00345.2002.-The modulation of serotonin (5-HT1B/1D) receptor-induced vascular contractility by histamine and U-46619 was compared in the rabbit basilar artery and saphenous vein. In the saphenous vein, histamine (5 ϫ 10 Ϫ7 M) significantly increased the potency (from pEC50 of 6.0 to 6.8) and efficacy (from 52.3% to 88.2%) of sumatriptan. Likewise, U-46619 (5 ϫ 10 Ϫ9 M) also increased the potency (from pEC50 of 5.9 to 6.6) and efficacy (from 51.8% to 92.1%) of sumatriptan in the saphenous vein. In contrast, equieffective concentrations of histamine (10 Ϫ7 M) and U-46619 (3 ϫ 10 Ϫ9 M) failed to amplify contraction to sumatriptan in the basilar artery. Contraction to sumatriptan was inhibited by nitrendipine (10 Ϫ7 M) in the basilar artery but not in the saphenous vein, suggesting that different contractile signaling mechanisms are operating in these tissues. Furthermore, U-46619-and thrombin-induced contractility in the basilar artery were also not amplified by histamine, suggesting that lack of amplification of contraction in the basilar artery was not restricted to sumatriptan but was rather a characteristic of this cerebral vessel. These data suggest that in the in vivo plasma milieu sumatriptan will more markedly contract the peripheral saphenous vein than the basilar artery, a cerebral blood vessel. nitrendipine; histamine; U-46619; serotonin receptors SUMATRIPTAN is an antimigraine drug (20) with a high affinity for serotonin 5-HT 1B and 5-HT 1D receptors (27). The antimigraine efficacy of sumatriptan has been attributed, in part, to its ability to activate central vascular 5-HT 1B/1D receptors (8). However, much of the information on the vascular effects of sumatriptan has been derived from studies using peripheral vascular serotonin receptors. For example, sumatriptan-induced peripheral vascular contraction has been widely studied in the rabbit saphenous vein (9), femoral artery (4), mesenteric artery (5), and iliac artery (36). Because the cardiovascular liabilities of sumatriptan may be related to its ability to constrict coronary arteries (23), sumatriptan has also been studied in coronary arteries from dogs (21) and humans (1). In contrast, the cerebral vascular effects of sumatriptan have been less extensively studied (3,16,17).Modest increases in vascular tone with threshold concentrations of vascular contractile agonists such as prostaglandin, angiotensin, histamine, endothelin, or adrenergic agonists are known to increase sumatriptaninduced vascular contractility (35). Whereas this amplifying effect is well established in peripheral blood vessels (7,9,21,22