The Studies on the Contractile Response of Serotinin in Rat Aorta

ABSTRACT

The mechanism of serotonin(5-HT) induced contraction and Ca++ mobilization was investigated in right cut from rat aorta. Since it is known that 5-HT can interact with alpha-adrenoceptors in addition to a specific action on 5-HT receptors, the effects alpha-adrenoceptors antagonists on these contractile responses to 5-HT were investigated. The results are as follows 1) 5-HT produced a strong transient contraction and a concentration dependent contraction. 2) The contractile tension to 5-HT increased with extracellular Ca++ concentration (0.1-5mM). 3) The response produced by rings exposed to Ca++-free PSS was significantly weaker than that produced by rings exposed to calcium containing PSS. When rings of aorta that had been stimulated with 5-HT once for 30 min in Ca++-free TBT were washed 4 times for at least; 20 min in zero Ca++PSS to remove 5-HT, than reexposed to 5-HT in Ca++-free TBT, a phasic contraction was not seen during the second stimulation with 5-HT. 4) The contractile response of 5-HT was inhibited by alpha-adrenergic receptor blocker, phenoxybenzamine and phentolamine. Phentolamine(10(-8)M) antagonized response to high concentrations of 5-HT but responses to low concentrations of 5-HT were not antagonized. 5) The contraction induced by 5-HT in Ca++-free PSS was investigated with phentolamin, methysergide. It was blocked by methysergide but not blocked by phentolamine. 6) These results suggest that 5-HT -induced contraction is the effect of both transmembrane Ca++ influx and the mobilization of intracellular Ca++. Low concentration of 5-HT act on specific 5-HT receptors but high concentration of 5-HT also act on alpha-adreno-receptors.