Ho. Kalkman et F. Schneider, EFFECTS OF ERGOTAMINE AND DIHYDROERGOTAMINE ON 5-HYDROXYTRYPTAMINE-2ARECEPTORS IN THE ISOLATED RAT AORTA, Pharmacology, 53(6), 1996, pp. 351-355
Ergotamine contracted isolated rat aorta rings with an intrinsic activ
ity of 50% of that of 5-hydroxytryptamine (5-HT, 0.1 mmol/l). Dihydroe
rgotamine did not contract the tissue, but insurmountably blocked cont
raction in response to ergotamine and 5-HT. The 5-HT2A receptor antago
nist, ketanserin (0.1 mu mol/l), inhibited ergotamine (pK(B) 8.0) and
5-HT (pK(B) 8.1) induced contractions. These results indicate that in
the rat aorta ergotamine is a partial 5-HT2A receptor agonist, whilst
dihydroergotamine is an insurmountable 5-HT2A receptor antagonist. The
present data could explain why ergotamine displays more cardiovascula
r and uterotonic side effects than dihydroergotamine.