Agonist-directed trafficking explaining the difference between response pattern of naratriptan and sumatriptan in rabbit common carotid artery.

1. Sumatriptan or eletriptan produced vasocontraction in common carotid artery (CCA) by stimulating 5HT(1B) receptors (see also Akin & Gurdal, this issue). 2. Naratriptan as a 5HT(1B/D) agonist, was unable to produce vasocontraction in this artery, but inhibited the vasocontractile response induced by sumatriptan or eletriptan. 3. All these agonists inhibited forskolin-stimulated cyclic AMP production with comparable potencies and maximal responses. This inhibition was mediated by 5HT(1B) receptors: 5HT(1B) antagonist SB216641 (1 microM) completeley antagonized sumatriptan-, eletriptan- or naratriptan-induced cyclic AMP inhibition, but 5HT(1D) antagonist BRL15572 (1 microM) did not affect this response. 4. Naratriptan-induced stimulation of 5-HT(1B) receptors resulted only in adenylate cyclase inhibition, whereas stimulation of these receptors by sumatriptan or eletriptan produced vasocontraction as well. Hence, we concluded that the 5HT(1B)-mediated inhibition of adenylate cyclase was not a sufficient condition to couple the receptor stimulation to vasocontraction. 5. We discussed agonist-induced trafficking as a plausible mechanism for the observed phenomenon.