The interaction of eight typical representatives of naturally occurring clavines (agroclavine, costaclavine, dihydrolysergol-I, elymoclavine, festuclavine, lysergene, lysergol, and pyroclavine) with 5-HT2A receptors and α1-adrenoceptors was studied in rat tail artery and aorta, respectively. Clavines antagonized 5-HT-induced contractions with calculated pKB values (pKP values for partial agonists) of 4.84-7.81 and (R)-phenylephrine-induced contractions with calculated pKB values of 5.34-7.09. Specificity of clavines at 5-HT2A receptors relative to α1 adrenoceptors was rather low. Low affinity for costaclavine at both 5-HT2A receptors (pKP = 4.84 ± 0.06) and α1-adrenoceptors (pKB = 5.34 ± 0.05) indicates that the trans-junction of ring C and D of the ergoline pharmacophore is crucial for the binding of ergolines to these sites. Lysergol, lysergene, and costaclavine produced non-parallel displacements of the 5-HT concentration-response curve in the rat tail artery and caused small contractions by themselves. Lysergol contracted the rat tail artery with a pEC50 of 6.36 ± 0.04 and an intrinsic activity of 0.18 ± 0.03 with respect to 5-HT. Lysergol-induced contractile responses were surmountably antagonized by ketanserin (10 nM) with a pKB of 9.1 which is consistent with an interaction of lysergol with 5-HT2A receptors. The pKP for the lysergol-5-HT2A receptor complex calculated from concentration-response curves to lysergol was 6.88 ± 0.07 and did not match the pKP of 7.66 ± 0.02 calculated from antagonism by lysergol of the contractile response to 5-HT. This suggests that lysergol and 5-HT possibly bind in two slightly different orientations at the 5-HT2A receptor. It is concluded that partial agonism and pure antagonism at 5-HT2A receptors on the one side and antagonism at α1-adrenoceptors on the other side may contribute to the noxious effects of naturally occurring clavines.
研究了大鼠尾动脉和主动脉中八种自然产生的clavines(田
麦角碱、肋
麦角碱、
二氢麦角考宁-I、elymoclavine、festuclavine、
麦角胺、
麦角醇和
吡咯clavine)与5-HT2A受体和α1-
肾上腺素受体的相互作用。Clavines拮抗了5-HT引发的收缩,计算的pKB值(部分激动剂的pKP值)为4.84-7.81,以及(R)-苯
肾上腺素引发的收缩,计算的pKB值为5.34-7.09。在5-HT2A受体相对于α1
肾上腺素受体方面,clavines的特异性相当低。肋
麦角碱对5-HT2A受体(pKP = 4.84 ± 0.06)和α1-
肾上腺素受体(pKB = 5.34 ± 0.05)的低亲和力表明,ergoline药效团的C环和D环的反式连接对于ergolines与这些位点的结合至关重要。
麦角醇、
麦角胺和肋
麦角碱在鼠尾动脉中产生了非平行的5-HT浓度-反应曲线位移,并自身引起轻微的收缩。
麦角醇使鼠尾动脉收缩,p
EC50为6.36 ± 0.04,相对于5-HT的内在活性为0.18 ± 0.03。
麦角醇引发的收缩反应可以被
酮舍林(10 nM)以pKB为9.1的值所拮抗,这与
麦角醇与5-HT2A受体的相互作用一致。从
麦角醇的浓度-反应曲线计算出的
麦角醇-5-HT2A受体复合物的pKP为6.88 ± 0.07,与从
麦角醇对5-HT收缩反应的拮抗作用计算出的pKP 7.66 ± 0.02不符。这表明
麦角醇和5-HT可能在5-HT2A受体上有两种稍微不同的取向。总之,部分激动和纯拮抗5-HT2A受体,以及α1-
肾上腺素受体的拮抗作用,可能有助于自然产生的clavines的有害效应。