脊髓5-HT_(1A)受体和5-HT_(3)受体参与的心血管反应

CARDIOVASCULAR REACTIONS MEDIATED BY 5-HT_(1A)AND 5-HT_(3) RECEPTORS IN THE SPINAL CORD OF CONSCIOUS RATS

给清醒大鼠脊髓蛛网膜下腔注射(ith)5-羟色胺(5-HT)1.56、3.125、6.25和12.5μg/1Oμl后引起明显血压升高,并呈量效关系,但心率(HR)无明显改变。Ith 5-HT 再摄取抑制剂 fluoxetine(10μg/10μ1)后也使平均动脉压(mABP)明显上升,这一效应可被5-HT 受体阻断剂肉桂硫胺(cinanserin 25μg/1Oμl)完全阻断。8-OH-DPAT 和2-Methylhydroxy-tryptamine 分别为5-HT_(1A)受体和5-HT_3受体的激动剂,在 ith 8-OH-DPAT(2.5,5.0,1Oμg/1Oμl)后 mABP 明显上升,但 HR 减慢;相反,ith 2-Methylhydroxytryptamine 之后则使 mABP 明显降低,HR 无明显变化。以上结果表明,脊髓中5-HT 可通过激活5-HT_(1A)受体引起血压升高,激活5-HT_3受体则引起血压降低。这一发现对有关5-HT 中枢效应的不同报道提出了一种可能的解释。

Intrathecal administration(ith)of 5-hydroxytryptamine(5-HT,1.56,3.125,6.25 and 12.5 μg/10μl)to conscious rats produced a marked dose-dependent hy-pertensive effect without significant change in heart rate(HK).Ith administra-tion of fluoxetine(10μg/μl),one of the presynaptic reuptake inhibitors of 5-HT,produced a marked increase in the mean arterial blood pressure(mABP).Thiseffect could be prevented by a pretreatment with cinanserin(25μg ith)as a blockerof 5-HT receptor.It was further observed that ith of 8-OH-DAPT(2.5,5,10μg/10μl),a 5-HT_(1A)receptor agonist,produced a dose-dependent increase of mABPand lowering of HR.However,ith of 5-HT_3 receptoI agonist 2-Methylserotonin(25,50,100 μg/10μl),decreased mABP markedly without change in HR.The results indicate that 5-HT in the spinal cord may exerta hypertensiveeffect via 5-HT_(1A) receptor and a hypotensive effect via 5-HT_3 recep-tor.This givesa possible explanation about the conflicting reports concerningthe effec of 5-HTin the central nervous system on blood pressure.