Enhanced contractile responses mediated by different 5-HT receptor subtypes in basilar arteries, superior mesenteric arteries and thoracic aortas from stroke-prone spontaneously hypertensive rats.

1. The contractile effects of 5-hydroxytryptamine (5-HT) in isolated ring preparations of basilar arteries (BA) thoracic aortas (TA) and superior mesenteric arteries (SMA) from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats were investigated pharmacologically. 2. The pD2 values (expressed as a negative logarithm of of EC50) for 5-HT in BA of SHRSP were greater than those of WKY. Increased pD2 values for 5-HT were also found in SMA and TA of SHRSP when compared to WKY. 3. Ketanserin (a 5-HT2 antagonist) produced a biphasic displacement of the concentration-response curves for 5-HT in BA of WKY and SHRSP but elicited a parallel rightward shift of the 5-HT curve in SMA and TA of the two groups. 4. 5-CT (a 5-HT1 agonist)-induced contractions and their pD2 values in the presence of ketanserin were larger in BA of SHRSP than in those of WKY, while 5-CT did not contract SMA or TA in either group. 5. No significant difference was found in the contractile response induced by alpha-methyl-5-HT (a 5-HT2 agonist) in BA from SHRSP and WKY, while the pD2 values for alpha-methyl-5-HT were increased in SMA and TA from SHRSP when compared to WKY. 6. These results suggest that the hyperresponsiveness to 5-HT found in SHRSP arteries may be mediated by different 5-HT receptor subtypes, that is, by 5-HT1 in BA and by 5-HT2 in SMA and TA.