No contractile effect for 5-HT1D and 5-HT1F receptor agonists in human and bovine cerebral arteries: similarity with human coronary artery

Abstract

1. Using subtype-selective 5-HT1 receptor agonists and/or the 5-HT1 receptor antagonist GR127935, we characterized in vitro the 5-HT receptor that mediates the contraction of human and bovine cerebral arteries. Further, we investigated which sumatriptan-sensitive receptors are present in human coronary artery by reverse-transcriptase polymerase chain reaction (RT-PCR). 2. Agonists with affinity at the 5-HT1B receptor, such as sumatriptan, alniditan and/or IS-159, elicited dose-dependent contraction in both human and bovine cerebral arteries. They behaved as full agonists at the sumatriptan-sensitive 5-HT1 receptors in both species. In contrast, PNU-109291 and LY344864, selective agonists at 5-HT1D and 5-HT1F receptors, respectively, were devoid of any significant vasocontractile activity in cerebral arteries, or did not affect the sumatriptan-induced vasocontraction. The rank order of agonist potency was similar in both species and could be summarized as 5-HT = alniditan > sumatriptan = IS-159 >>> PNU-109291 = LY344864. 3. In bovine cerebral arteries, the 5-HT1 receptor antagonist GR127935 dose-dependently inhibited the vasoconstrictions elicited by both 5-HT and sumatriptan, with respective pA2 values of 8.0 and 8.6. 4. RT-PCR studies in human coronary arteries showed a strong signal for the 5-HT1B receptor while message for the 5-HT1F receptor was weak and less frequently detected. Expression of 5-HT1D receptor mRNA was not detected in any sample. 5. The present results demonstrate that the triptan-induced contraction in brain vessels is mediated exclusively by the 5-HT1B receptor, which is also present in a majority of human coronary arteries. These results suggest that selective 5-HT1D and 5-HT1F receptor agonists might represent new antimigraine drugs devoid of cerebro- and cardiovascular effects.

Figure 1

Concentration-response curves for 5-HT, sumatriptan, alniditan, IS-159, PNU-109291 and LY344864 in human cerebral arteries under resting tension. The E_Amax for each agonist is expressed as a percentage of 5-HT_EAmax measured in the same vascular segments. Complete information on potency, maximal response and number of vascular segments is given in Table 1. Vertical bars show s.e.mean of n=5–8.

Figure 2

Concentration-response curves for 5-HT, sumatriptan, alniditan, PNU-109291 and LY344864 in bovine cerebral arteries under resting tension. The E_Amax for each agonist is expressed as a percentage of 5-HT E_Amax obtained in the same vascular segments. See Table 2 for detailed information on individual potency, maximal response and number of vascular segments. Vertical bars indicate s.e.mean of n=10–12.

Figure 3

(A) Concentration-response curves for 5-HT in bovine cerebral arteries in the absence (control) and in presence of various concentrations (10⁻⁸–10⁻⁶ M) of GR127935. Values are expressed as percentage of the 5-HT E_Amax measured in the same arterial segments and are means±s.e.means of n=20, 7, 11 and 9, respectively. (B) Schild plot analysis of the effect of GR127935 on 5-HT-induced contraction of bovine cerebral arteries (r=0.99, slope of 1.20±0.02).

Figure 4

(A) Concentration-response curve for sumatriptan in bovine arteries in the absence (control) and in the presence of various concentrations (10⁻⁹–10⁻⁷ M) of GR127935. Values are expressed as percentage of the sumatriptan E_Amax measured in the same arterial segments and are means±s.e.means of n=18, 5, 7, and 6, respectively. (B) Schild plot analysis of the effect of GR127935 on sumatriptan-induced contraction of bovine cerebral arteries (r=0.96, slope of 0.68±0.20).

Figure 5

Identification of sumatriptan-sensitive 5-HT₁ receptors in human coronary artery (CA) by RT–PCR. Representative agarose gel electrophoresis of PCR products showing the absence of 5-HT_1D receptors in human coronary artery despite consistent amplification in the human trigeminal ganglion (TG). High intensity PCR products were obtained for 5-HT_1B receptors in 60% of human coronary arteries while a weak signal was obtained for the 5-HT_1F receptor in 40% of cases. Samples without reverse transcriptase (−) were included to monitor for possible contamination.