“…The 5‐HT 1 receptor agonist sumatriptan was found to elicit a contraction of both human and bovine cerebral arteries, with a potency similar to that reported in previous studies in human (Parsons, 1991; Hamel et al ., 1993b), bovine (Hamel et al ., 1993b) and dog (Beattie & Connor, 1995) cerebral arteries. In bovine cerebral arteries, the maximal response elicited by sumatriptan and other 5‐HT 1 receptor agonists was predictably less than that of 5‐HT, but was also slightly smaller than that reported previously by us for sumatriptan in the same preparation (Hamel et al ., 1993b), probably a consequence of the seasonal variations in contractile 5‐HT receptors (Vinall et al ., 1991). The difference between 5‐HT and sumatriptan maximal response, however, is most likely due to the participation of 5‐HT 2A receptors in the 5‐HT‐mediated vasoconstriction in this species (Frenken & Kaumann, 1984; De Wever et al ., 1990; Foy et al ., 1992), a population of receptors which is either not present or not functional in human brain vessels (Hamel & Bouchard, 1991; Kaumann et al ., 1993).…”