THE ONTOGENY OF BLADDER FUNCTION IN THE FETAL CALF

Although numerous experimental studies have addressed urinary bladder physiology and pharmacology, little information is available concernin g the ontogeny of bladder function. The present in vitro study describ es the developmental aspects of bladder compliance, pressure generatio n and emptying in bovine fetuses from early second trimester to term ( 280 days). The results can be summarized as follows: 1) bladder compli ance increased S-fold between early second trimester and term; 2) sust ained contractile response to bethanechol was present in all bladders; 3) field stimulation produced a submaximal, nonsustained contraction and an active relaxation when the field stimulus was turned off; 4) bl adder emptying in response to bethanechol was nearly 100% in mid- and late-gestational bladders but was only 50% at early gestation; 5) blad der emptying in response to field stimulation was 20% to 40% for all g estational age groups; 6) field stimulated relaxation was observed onl y in the fetal bladder. These studies demonstrate that bladder physiol ogy in utero is different from postnatal bladder function. The presenc e of a relaxant response during the fetal period may reflect a unique and significant role of the in utero bladder in protecting the upper u rinary tracts from sustained increased pressure.