Functional serotonin and histamine receptor subtypes in porcine ciliary artery in comparison with middle cerebral artery

Functional serotonin (5-HT) and histamine receptor subtypes were investigated in porcine middle cerebral and ciliary arteries. An H1 antagonist, mepyramine, antagonized histamine-induced responses with pKB values of 8.91–9.10. In the presence of 1 μM mepyramine, however, histamine caused dilation through H2 receptors in the middle cerebral but not in the ciliary artery. A 5-HT2A antagonist, ketanserin, antagonized 5-HT-induced responses, causing rightward shifts in the concentration–response curves with pKB values of 8.52–8.71. A 5-HT1B antagonist, SB224289, produced rightward shifts of the concentration–response curves to sumatriptan with pKB values (6.66) only in the middle cerebral artery. In contrast, a 5-HT1D antagonist, BRL15572, had no effect in either artery. An RT-PCR study demonstrated the gene expression of the mRNAs of all three receptors (5HT1B, 5HT1D and 5HT2A) in both arteries. These results suggest that histamine-induced contraction is mediated only through functional H1 receptor in these arteries. Interestingly, there are functional 5-HT2A and 5-HT1B receptor subtypes in the middle cerebral artery, whereas the only functional receptor is 5-HT2A in the ciliary artery. The difference may be important for treatment with 5-HT1B/1D agonists (e.g. for migraine) without ocular side effect.