CHARACTERIZATION OF 5-HYDROXYTRYPTAMINE RECEPTORS IN GOAT CEREBRAL-ARTERIES

1.In isolated goat middle cerebral artery segments, 5-hydroxytryptamine (5-HT, 10(-8)-3 x 10(-5) M) elicited concentration-dependent contractions with EC(50) = 2.1 (1.9-2.5) x 10(-7) M and E(max) = 64 +/- 2% of 50 mM KCl-induced contraction. 2. Several 5-HT receptor agonists were used: (a) the agonist of 5-HT2 receptors alpha-methyl-5-hydroxytryptamine (10(-7)-3 x 10(-4) M) induced strong contraction (51 +/- 6%); (b) the selective agonists of 5-HT1 receptors sumatriptan (10(-8)-10(-5) M) and 5-carboxamidotryptamine (10(-9)-10(-4) M) and the agonist of 5-HT1A receptors 8-hydroxy-2-(di-n-propylamino)tetralin (10(-7)-3 x 10(-5) M) induced weak contractions (8, 18 and 14%, respectively); and (c) the agonist of 5HT(3) receptors 2-methyl-5-hydroxytryptamine (3 x 10(-6)-10(-4) M) induced almost negligible contraction. 3. Pretreatment with the antagonist of 5-HT1A and 5-HT1B receptors cyanopindolol (10(-8), 10(-6) M), the antagonist of 5-HT1/5-HT2 receptors methysergide (10(-11), 10(-9)M) and the antagonist of 5-HT2 receptors ketanserin (10(-11), 10(-9) M) induced non-competitive inhibition of the concentration-response curve to 5-HT. The antagonist of 5-HT3 receptors 3-trophanyl-3,5-dichlorobenioate (10(-7), 10(-5) M) did not inhibit the contractile curve to 5-HT. 4. These results suggest that 5-HT contracts the goat middle cerebral artery by acting mainly on 5-HT2 receptors.