Effect of catecholamine on fetal breathing activity in rhesus monkeys

The effect of various catecholamines on fetal breathing movements (FBM) was studied in 10 established chronic fetal rhesus monkey preparations. Norepinephrine, epinephrine, isoproterenol (all 1:10⁵[ w v] in concentration), or saline was infused intravenously to the fetus, each on five separate occasions. The infusion of the catecholamines was started at 0.02 ml/min and increased in a stepwise fashion until the fetus exhibited cardiovascular responses. The infusion rate was then maintained for 30 minutes to observe FBM. The incidence of FBM was determined for each 5-minute period and also expressed as a percentage of preinfusion values. Statistical analysis revealed that the incidence of FBM was significantly increased by isoproterenol and decreased by norepinephrine. Epinephrine did not consistently alter the incidence of the FBM.