EFFECT OF ATRIAL-NATRIURETIC-PEPTIDE ON BRONCHIAL TONE IN ANESTHETIZED RABBITS

The effect of atrial natriuretic peptide (ANP) on histamine-induced br onchoconstriction was studied in vivo (in normoxic and in hypoxic rabb its) and in vitro. Thirty-two anesthetized rabbits, spontaneously brea thing room air or 10% 02, received infusions of ANP (20, 40, or 80 ng/ min/kg normoxia; 20 ng/min/kg hypoxia) or the vehicle for 100 min. Aft er 75 min of ANP infusion, bronchoconstriction was induced inhaling hi stamine; respiratory resistance (Rrs) was measured prior to and until 20 min posthistamine. The results show that the histamine-induced incr ease in Rrs was significantly reduced by ANP 80 ng/kg/min in normoxia, and by ANP 20 ng/kg/min in hypoxia. In vitro, ANP had no effect on tr acheal and bronchial smooth muscle precontracted with histamine or ace tylcholine. These results show that ANP can decrease a histamine-induc ed bronchoconstriction in vivo but not in vitro, suggesting an indirec t mechanism of action.