Characterization of 5-Hydroxytryptamine receptors in goat cerebral arteries

1. 1. In isolated goat middle cerebral artery segments, 5-hydroxytryptamine (5-HT, 10 −8-3 × 10 −5 M) elicited concentration-dependent contractions with EC 50 = 2.1 (1.9−2.5) × 10 −7 M and E max = 64 ± 2% of 50 mM KCl-induced contraction. 2. 2. Several 5-HT receptor agonists were used: (a) the agonist of 5-HT 2 receptors α-methyl-5-hydroxytryptamine (10 −7 -3 × 10 −4 M) induced strong contraction (51± 6%); (b) the selective agonists of 5-HT 1A receptors sumatriptan (10 −8 - 10 −5 M) and 5-carboxamidotryptamine (10 −9 - 10 −4 M) and the agonist of 5-HT 1A receptors 8-hydroxy-2-(di-n-propylamino)tetralin (10 −7 - 3 × 10 −5 M) induced weak contractions (8, 18 and 14%, respectively); and (c) the agonist of 5HT 3 receptors 2-methyl-5-hydroxytryptamine (3 × 10 −6 - 10 −4 M) induced almost negligible contraction. 3. 3. Pretreatment with the antagonist of 5-HT 1A and 5-HT 1B receptors cyanopindolol (10 −8, 10 −6 M), the antagonist of 5-HT 1/5-HT 2 receptors methysergide (10 −11, 10 −9 M) and the antagonist of 5-HT 2 receptors ketanserin (10 −11, 10 −9 M) induced non-competitive inhibition of the concentration-response curve to 5-HT. The antagonist of 5-HT 3 receptors 3-trophanyl-3,5-dichlorobenzoate (10 −7, 10 −5 M) did not inhibit the contractile curve to 5-HT. 4. 4. These results suggest that 5-HT contracts the goat middle cerebral artery by acting mainly on 5-HT 2 receptors.