ADRENOMEDULLIN SUPPRESSES ATRIAL-NATRIURETIC-FACTOR (ANF) SECRETION FROM ISOLATED ATRIUM

Atrial natriuretic factor (ANF) secretion was studied using isolated p erfused right atria prepared from rats. Adrenomedullin (ADM), a recent ly identified 52-amino acid peptide whose biological activity has a st riking resemblance to that of ANF, was added to the perfusate at a con centration of 1 mu g/ml. The concentration of ANF secreted into the pe rfusate was measured by radioimmunoassay, under basal conditions (atri al wall unstressed), and during atrial distention (intraluminal pressu re raised to 4 and to 6 cm water). It was found that basal secretion o f ANF was not altered by ADM. However, when intraluminal pressure was raised, there was a significantly smaller increase in ANF secretion in the ADM-infused atria than in the control atria. It is concluded that ADM significantly reduces stretch-induced secretion of ANF, while hav ing only minimal effects on basal secretion. Such an inhibitory mechan ism would ensure the necessary negative feedback mechanism to counter the previously-reported stimulatory actions of ANF on ADM secretion. M oreover, these results support the hypothesis that ADM could be respon sible for the reduction in stretch-induced ANF release observed during pregnancy.