The ontogeny of bladder function in the fetal calf

Abstract

Although numerous experimental studies have addressed urinary bladder physiology and pharmacology, little information is available concerning the ontogeny of bladder function. The present in vitro study describes the developmental aspects of bladder compliance, pressure generation and emptying in bovine fetuses from early second trimester to term (280 days). The results can be summarized as follows: 1) bladder compliance increased 3-fold between early second trimester and term; 2) sustained 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) bladder emptying in response to bethanechol was nearly 100% in mid- and late-gestational bladders but was only 50% at early gestation; 5) bladder emptying in response to field stimulation was 20% to 40% for all gestational age groups; 6) field stimulated relaxation was observed only in the fetal bladder. These studies demonstrate that bladder physiology in utero is different from postnatal bladder function. The presence of a relaxant response during the fetal period may reflect a unique and significant role of the in utero bladder in protecting the upper urinary tracts from sustained increased pressure.