Characteristics of Bradykinin-Evoked Secretory Response in the Perfused Rat Adrenal Medulla

Catecholamine secretion in the perfused rat adrenal medulla stimulated by bradykinin was characterized. The mean adrenaline secretion rate over the first 4 min after exposure to 100 nM bradykinin was 280 pmol/min. The secretion decreased by desensitization to 40% of the initial level within 20 min. The stimulant effect of bradykinin was removed by a 10-min washout but the desensitization persisted for longer periods. Although noradrenaline secretion was also evoked by bradykinin, it amounted to only 4% of the adrenaline secretion, which was markedly smaller as compared with 24% for acetylcholine (ACh)-evoked noradrenaline secretion. In a Ca2+-deficient medium, the bradykinin-evoked catecholamine secretion was reduced by 49% of the control (2 mM Ca2+), whereas the ACh-evoked secretion by 87%. The bradykinin-evoked secretion was almost completely inhibited in 1 mM EGTA-containing, Ca2+-free medium. The presence of a Ca2+ channel blocker, methoxyverapamil (D600) (100 μM) did not affect the bradykinin-evoked secretion but inhibited the ACh-evoked secretion by 80%. These results suggest that bradykinin leads to the catecholamine secretion by a pathway different from that for ACh.