Interaction between prejunctional alpha 2-receptors and neuronal transmitter reuptake in small mesenteric arteries...

The role of the prejunctional alpha 2-receptors for the response to vaso-constrictor nerve stimulation has been examined before and after inhibition of neuronal transmitter reuptake in mesenteric resistance vessels from the rat. Small arteries (diameter about 200 micron) feeding the jejunum were mounted in a myograph for recording of their isometric wall tension during transmural field stimulation of the intramural nerves. Blockade of prejunctional alpha 2-receptors with 0.01 microM idazoxan (RX 781094) caused a marginal potentiation of the neurogenic response when neuronal reuptake was left intact. Also, inhibition of reuptake alone with 3 microM cocaine had little effect on the response. However, when both alpha 2-receptors and reuptake had been inhibited, a strong enhancement of the neurogenic vasoconstriction was observed. Similar findings were made when yohimbine and LU 3-010 instead were used for alpha 2-blockade and reuptake inhibition, respectively. The results thus indicate that in these resistance arteries the effector response is normally influenced by the combined activity of alpha 2-receptors and uptake, and that failure of one mechanism increases the activity of the other, so as to maintain a largely constant effector response.