Functional characterization of the pre- and postjunctional alpha-adrenoceptors in the in situ perfused rat mesenteric vascular bed.

Pressor responses to periarterial nerve stimulation in the in situ perfused mesentery were potentiated by rauwolscine while responses to norepinephrine and phenylephrine were unaffected. Pressor responses to nerve stimulation, norepinephrine and phenylephrine were abolished by prazosin. No responses could be elicited in the mesentery by tramazoline. Thus, pressor responses to nerve stimulation and norepinephrine in this vascular bed are mediated by alpha 1-adrenoceptors while prejunctional alpha 2-adrenoceptors exert a negative feedback influence on vascular neurotransmission.