Lower urinary tract function in the sheep fetus: studies of autonomic control and pharmacologic responses of the fetal bladder.

An experimental preparation was developed to study fetal bladder function. In 16 fetal sheep at 120 days' gestation, two distinct types of bladder contractions were identified, one typical of contractions seen after birth and one phasic. Bladder capacity and intravesical pressure during contraction varied widely among fetuses, but residual urine was invariably less than one ml. Several drugs altered fetal bladder function: bethanechol decreased bladder capacity (6.8 vs. 13.6 ml.); atropine increased bladder capacity (27.3 vs. 6.8 ml.) and resulted in a 17-ml. residual urine; and ritodrine, magnesium sulfate and diltiazem inhibited bladder contractions and also resulted in residual urines of seven, six and seven ml. respectively. The fetal sheep bladder at 120 days' gestation is under both cholinergic and beta-adrenergic control. Further, drugs currently administered to pregnant women for the treatment of pre-term labor and pre-eclampsia cross the placenta and can directly alter bladder function in the developing fetus and the neonate.