RESUMO
Using a series of triptans we characterized in vitro the 5-hydroxytryptamine (5-HT) receptor that mediates the contraction in guinea-pig iliac arteries moderately precontracted by prostaglandin F2alpha (PGF2alpha). Additionally, we investigated by reverse-transcriptase polymerase chain reaction (RT-PCR) which triptan-sensitive receptor is present in this tissue. Frovatriptan, zolmitriptan, rizatriptan, naratriptan, sumatriptan, and almotriptan contracted guinea-pig iliac arteries with pD2 values of 7.52+/-0.04, 6.72+/-0.03, 6.38+/-0.06, 6.22+/-0.05, 5.86+/-0.05 and 5.26+/-0.04 respectively. For comparison, the pD2 values for 5-HT and 5-carboxamidotryptamine (5-CT) were 7.52+/-0.02 and 7.55+/-0.03 respectively. In contrast to all other triptans tested, the concentration-response curve for eletriptan was biphasic (first phase: 0.01-3 microM, pD2 approximately 6.6; second phase: > or = 10 microM). Contractions to 5-HT, 5-CT, frovatriptan, zolmitriptan, rizatriptan, naratriptan, sumatriptan, almotriptan, and eletriptan (first phase) were antagonized by the 5-HT1B/1D receptor antagonist GR127935 (10 nM) and the 5-HT1B receptor antagonist SB216641 (10 nM). RT-PCR studies in guinea-pig iliac arteries showed a strong signal for the 5-HT1B receptor while expression of 5-HT1D and 5-HT1F receptors was not detected in any sample. The present results demonstrate that triptan-induced contraction in guinea-pig iliac arteries is mediated by the 5-HT1B receptor. The guinea-pig iliac artery may be used as a convenient in vitro model to study the (cardio)vascular side-effect potential of anti-migraine drugs of the triptan family.
