Analysis of the 5-hydroxytryptamine induced contraction of the human basilar arterial strip compared with the rat aortic strip in vitro.

1. Experiments were performed to investigate the nature of the contraction produced by 5-hydroxytryptamine in the human basilar arterial strip in vitro and to compare it with that produced in the rat aortic strip in vitro. 2) The human basilar arterial strip was found to be significantly more sensitive to 5-HT compared to the rat aortic strip. 3) Methysergide, cyproheptadine and methergoline were competitive, selective antagonists against 5-HT on the rat aorta with pA2 values of 7.97, 8.76 and 9.49 respectively. In contrast 5-HT was antagonised by these agents in a manner which was not competitive on the human basilar artery. Both 5-HT and NA were antagonised by BW 501 C67 (alpha-anilino-N-2-m-chlorphenoxy propylacetamide hydrochloride) in a manner which was not competitive on both rat aortic and human basilar arterial strips. 4) Phentolamine (10(-7) to 10(-5) M) was found to be a competitive antagonist against noradrenaline on both the rat aortic strip (pA2 6.9) and the human basilar arterial strip (pA2 7.3). Phentolamine at 10(-5) M shifted the 5-HT curve on the human basilar artery to the right with a reduction in maximum response. 5) Methysergide (10(-9) to 10(-4) M) was found to possess contractile activity on some human basilar arterial strips, the maximum response being approximately 60% of that produced by 5-HT. Phentolamine at 10(-5) M shifted the dose-response curve to methysergide to the right with a slight reduction in the maximum response obtained. 6) The results from this study suggest that the receptor(s) mediating 5-HT-induced contraction of the human basilar artery may be different from the classical "D-receptor" which mediates contraction to 5-HT on the rat aorta.